Nano Res
1
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu
Zhang1()
Nano Res Just Accepted Manuscript bull DOI 101007s12274-014-0655-0
httpwwwthenanoresearchcom on November 28 2014
copy Tsinghua University Press 2014
Just Accepted
This is a ldquoJust Acceptedrdquo manuscript which has been examined by the peer-review process and has been
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which is identical for all formats of publication
Nano Research
DOI 101007s12274-014-0655-0
TABLE OF CONTENTS (TOC)
Fe3O4 nanoparticle-decorated TiO2
nanofiber hierarchical heterostructures
with improved lithium-ion battery
performance over a wide temperature
range
Heng-guo Wang Guang-sheng Wang
Shuang Yuan De-long Ma Yang Li and
Yu Zhang
Beihang University China
Fe3O4 nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures are fabricated
by combining the electrospinning technique with the hydrothermal method and the
resulting materials show improved lithium-ion battery performance over a wide
temperature range due to the synergistic effect of binary composition as well as the
unique feature of the hierarchical nanofibers
Provide the authorsrsquo webside if possible
Author 1 webside 1
Author 2 webside 2
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Received day month year
Revised day month year
Accepted day month year
(automatically inserted by
the publisher)
copy Tsinghua University Press
and Springer-Verlag Berlin
Heidelberg 2014
KEYWORDS
hierarchical
heterostructures wide
temperature range
Improved performance
lithium-ion batteries
ABSTRACT
A facile strategy was designed for the fabrication of Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures (FTHs)
through combining the versatility of the electrospinning technique and
hydrothermal growth method Hierarchical architecture of Fe3O4 nanoparticle
decorated on TiO2 nanofiber is designed for the successful integration of binary
components to address the structural stability and low capacity In the resulted
unique architecture of FTHs the 1D heterostructures relieve the strain caused
by severe volume change of Fe3O4 during the numerous charge-discharge
cycles and thus suppress the degradation of the electrode material As a result
FTHs show excellent performance including higher reversible capacity
excellent cycle life and good rate performance at wide temperature range due
to the synergistic effect of binary composition of TiO2 and Fe3O4 as well as the
unique feature of the hierarchical nanofibers
1 Instruction
In recent years rechargeable lithium-ion batteries
(LIBs) successfully capture the portable electronic
market because they have been considered as an
effective and green electrochemical energy storage
device However graphite the most commonly used
anode material in commercial LIBs have limited
theoretical capacity (372 mAh g-1) due to their
intercalation mechanism which is far from adequate
to meet the upcoming markets of electric
transportation and renewable energies There is a
general consensus that the breakthrough of energy
density necessarily requires passage from classical
intercalation reactions to conversion reactions [1-2]
Nano Research
DOI (automatically inserted by the publisher)
Address correspondence to Yu Zhang email jadebuaaeducn
Review ArticleResearch Article Please choose one
| wwweditorialmanagercomnaredefaultasp
2 Nano Res
However even after decade of intensive efforts the
application of conversion-based materials is still
seriously hampered by the terrible capacity
degradation and poor rate performance Therefore
there is highly desirable to simultaneously improve
cyclic life energy- and power- density of LIBs
Transition metal oxides (TMOs) are very
promising conversion-based anode materials which
exhibit many attractive advantages of low cost
environmental friendliness natural abundance and
especially much higher theoretical capacity (500-1000
mAh g-1) greatly spurring the rapid development of
this field [3-13] However TMOs still suffer from
poor cyclability that is associated with the severe
agglomerations and large volume change during
charge-discharge Alternatively TiO2 has been
investigated intensively because of its robustness in
cycle retention and chemical stability [14-17] The
very low volume change of less than 4 during Li+
insertionextraction intrinsically endows TiO2 the
enhanced structural stability and prolonged cycle life
[18-21] However the low theoretical capacity (168
mAh g-1) and the poor rate capability of TiO2 still
seriously hinder its widespread use in LIBs
Recently various metal oxidesTiO2
nanocomposites especially with one-dimensional
(1D) nanostructures have been suggested to
overcome the demerits of both materials thus
improving the anode performance in LIBs such as
MoO2TiO2 [22] Fe2O3TiO2 [2324] CoOTiO2 [25]
SnO2TiO2 [26-28] Also we have demonstrated the
successful integration of individual components into
the unique nanostructures could endow the
composite electrode materials with the improved LIB
performance [25] On one hand the presence of TiO2
stem can effectively maintain the mechanical
integrity of electrode materials during Li+
insertionextraction ions On the other hand not only
coating with metal oxides overcomes the high cost of
coating with noble metals (Au Ag etc) [2930] but
also the low specific capacity of TiO2 can be
compensated by the electroactive metal oxides with
high capacity However some rare transition metal
oxides are not suitable to be used for electrode
materials in the case of large-scale energy storage
from a viewpoint of the sustainability Fe-based
oxides otherwise are more earth-abundant low cost
and environmental friendliness Among these
Fe-based oxides Fe3O4 features both high capacity
and high electronic conductivity [31-39] thus its
coating on TiO2 nanofibers could be killing three
birds with one stone - the rate performance and
specific capacity of TiO2 nanofibers and the cycle life
of Fe3O4 nanoparticles could be simultaneously
improved by the synergistic effect between Fe3O4 and
TiO2 This inspires us to design Fe3O4TiO2 composite
materials to investigate the synergistic effect of
binary composition and the unique nanostructures
thus preparing anode materials with improved LIB
performance
Herein Fe3O4 nanoparticle-decorated TiO2
nanofiber hierarchical heterostructures (FTHs) were
prepared by combining the electrospinning and the
hydrothermal method TiO2 nanofiber is chosen as
stems to induce the growth of heterostructured Fe3O4
nanoparticle Interestingly the TiO2 stem could
maintain the structural integrity and the sufficient
interspaces between Fe3O4 nanoparticles could
accommodate the volume expansion of Fe3O4 during
chargedischarge process So when FTHs are tested
as anode materials for LIBs it shows excellent
performance including higher reversible capacity
excellent cycle life and good rate performance at
wide temperature range due to the synergistic effect
of binary composition of TiO2 and Fe3O4 as well as
the unique feature of the hierarchical nanofibers
2 Experimental
21 Synthesis of FTHs
The hierarchical Fe3O4TiO2 nanofibers were
synthesized by the electrospinning technique and
hydrothermal method [25] In a typical process
electrospun TiO2 nanofibers (20 mg) were put into
Teflon-lined autoclave (50 mL) with a ethylene glycol
(EG 25 mL) solution consisting of FeCl3middot6H2O (025 g)
polyethylene glycol (PEG 025 g) and sodium
acetate (NaAc 09 g) After the autoclave was sealed
and heated at 200 for 16 h the as-obtained
composite was collected out washed with ethanol
and deionized water respectively and then dried
under vacuum at 50 for 12 h For comparison the
TiO2Fe3O4 nanofibers with few secondary Fe3O4
nanoparticles (FTHfs) were also prepared by adding
FeCl3middot6H2O (005 g) and the free Fe3O4 nanoparticles
were also prepared without the addition of TiO2
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
3 Nano Res
nanofibers
22 Characterization
Scanning electron microscopy (SEM) images were
collected with a Hitachi S-4800 instrument
Transmission electron microscope (TEM) images
were carried out with a Tecnai G2 using 200 kV X-ray
diffraction (XRD) patterns were carried out with a
Rigaku-Dmax 2500 diffractometer using Cu Kα
radiation X-ray photoelectron spectroscopy (XPS)
analysis was conducted with ESCALAB MK II X-ray
instrument
23 Electrochemical Evaluation
70 wt active materials (FTHs FTHfs TiO2
nanofibers Fe3O4 nanoparticles and TiO2-Fe3O4
mixture) 20 wt acetylene black and 10 wt
polyvinylidene fluoride (PVDF) were mixed in
N-methyl-2-pyrrolidone (NMP) and then uniformly
pasted on copper foil After finally dried in vacuum
at 80 for 12 h to remove the solvent the work
electrodes were pressed and cut into disks Thin
lithium foil was used as the counter electrode
Celgard 2400 membrane was used as separator and
lithium hexafluorophosphate LiPF6 (1 M) in ethylene
carbonatedimethyl carbonate (ECDMC 11 vol )
was employed as the electrolyte Galvanostatic
chargedischarge experiments were conducted in a
voltage range of 001-30 V with a Land Battery
Measurement System (Land China) The cyclic
voltammetry (CV 001-3 V 01 mV s-1) and
electrochemical impedance spectroscopy (EIS 01-700
kHz 5 mV) were conducted using a VMP3
Electrochemical Workstation (Bio-logic Inc)
3 Results and discussion
Scheme 1 illustrates the overall synthesis procedure
employed for the preparation of FTHs which is
briefly composed of the electrospinning and the
hydrothermal method Herein no surface
pretreatments are needed to introduce new surface
functional groups or additional covalent andor
noncovalent interconnectivity As a result perfectly
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures were obtained in high
yield The morphology of the prepared samples is
characterized by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) Fig 1(a)
and 1(b) show SEM images of bare TiO2 nanofibers
and FTHs The bare TiO2 non-woven nanofibers with
average diameter about 220 nm (Fig 1(a) inset) have
a relatively smooth surface The resulting materials
show hierarchical nanostructure and have diameters
of about 250 nm (Fig 1(b) inset) From TEM image in
Fig 1(c) it is obvious that the secondary Fe3O4
nanoparticles grow on the surface of TiO2 nanofibers
From the High-resolution transmission electron
microscopy (HRTEM) image of the heterojunction
region (Fig 1(d)) the observed two set of lattice
fringe spacings of 035 and 0254 nm are consistent
with the (101) plane of the anatase crystal structure of
TiO2 and the (311) plane of the cubic magnetite Fe3O4
respectively From the HRTEM image (Fig 1(e)) of
the nanoparticle it is also concluded that the
secondary Fe3O4 nanoparticles successfully grow on
the surface of the TiO2 nanofibers Furthermore
energy-dispersive X-ray spectroscopy (EDS)
characterization (Fig S1 in the Electronic
Supplementary Material (ESM)) also confirms that
FTHs include Fe Ti and O indicating the presence
of both Fe3O4 and TiO2 And EDS line scanning along
the cross section of FTHs (Fig 1(f)) further shows
that Fe is present only outside the TiO2 nanofibers
but not inside As a result Fe3O4
nanoparticle-decorated TiO2 nanofiber results in the
formation of the hierarchical Fe3O4TiO2 coreshell
nanofibers Moreover the thicknesses of the
secondary Fe3O4 nanoparticles are controllable by
simply changing the experimental parameters (Fig
S2 in the ESM)
The crystallographic structure of the prepared
samples is investigated by powder X-ray diffraction
(XRD) As shown in Fig 2(a) all the diffraction peaks
could be indexed to anatase TiO2 (JCPDS file No
21-1272) and cubic magnetite Fe3O4 (JCPDS file No
19-0629) X-ray photoelectron spectroscopy (XPS)
characterization is further carried out to analyze the
elemental composition As shown in Fig 2(b) the
XPS spectrum of FTHs shows the presence of the
Ti2p O1s and Fe2p peak For the high-resolution
Fe2p (Fig 2(b) inset) it is observed that two peaks of
Fe2p32 and Fe2p12 appear at 711 and 724 eV
respectively which demonstrates the secondary
nanostructures are Fe3O4 Then inductively coupled
plasma atomic emission spectrometry (ICP-AES) is
also carried out to test the actual iron contents in
| wwweditorialmanagercomnaredefaultasp
4 Nano Res
each sample The results show that the iron contents
are 140 and 182 wt in FTHs with few secondary
Fe3O4 nanoparticles (FTHfs) and FTHs respectively
The electrochemical performance of FTHs is
investigated as anode materials for LIBs Fig 3(a)
shows its cyclic voltammetry (CV) curves Two pairs
of redox current peaks can be clearly identified
during the cathodic and anodic scans In the first
cycle two current peaks appear at ~175 and ~21 V
respectively which can be regarded as the signature
of the lithium insertionextraction processes in the
anatase framework In addition the sharp reduction
peak at ~07 V can be ascribed to the conversion of
Fe3O4 to Fe and the formation of amorphous Li2O as
well as their irreversible reaction with the electrolyte
which may lead to the irreversible capacity At the
same time the wide oxidation peak at ~17 V could
be assigned to the reversible oxidation of Fe0 to Fe3+
during the anodic process [3839] For comparison
bare TiO2 nanofibers and Fe3O4 nanoparticles are also
tested The two pairs of well-shaped redox peaks for
TiO2 nanofibers (Fig S3(a) in the ESM) and Fe3O4
nanoparticles (Fig S3(b) in the ESM) are in good
agreement with those for FTHs Note that as
expected there is only a slight decrease in the peak
current during the subsequent cycles for TiO2
nanofibers indicating the highly reversible redox
reactions of TiO2 nanofibers In contrast the peak
current of the redox peaks of Fe3O4 nanoparticles
drops dramatically during the subsequent scans
indicating seriously irreversible reactions have taken
place in the Fe3O4 electrode thus leading to a severe
capacity fading upon charge-discharge cycling
Therefore we anticipate the reinforcement of Fe3O4
nanoparticles by stable TiO2 nanofibers can
effectively alleviate the severe capacity fading
Fig 3(b) shows the discharge-charge curves of
FTHs at 100 mA g-1 Consistent with the above CV
analysis two discharge plateaus at ~175 and 07 V
and two charge plateaus at ~17 and 21 V can be
clearly observed These voltage profiles are
characteristic of both Fe3O4-based and TiO2-based
materials The initial discharge and charge capacities
are found to be 7836 and 4945 mAh g-1 respectively
corresponding to a Coulombic efficiency of 631
Furthermore in the successive cycles the capacity of
the electrode scarcely decays and it can still deliver a
reversible capacity of 4545 mAh g-1 even after 200
cycles (Fig 3(b) and 3(c)) On the contrary the bare
TiO2 nanofibers electrode only exhibits a lower
reversible capacity of 202 mAh g-1 (Fig S4(a) in the
ESM) Although the Fe3O4 nanoparticles exhibits
higher initial discharge capacity of 10634 mAh g-1
(Fig S4(b) in the ESM) it suffers severe capacity
fading (decrease to 1577 mAh g-1 only after 70 cycles)
(Fig S4(c) in the ESM) which is lower than that of
FTHs indicating that the successful integration of
binary TiO2-Fe3O4 components can favourably inherit
the respective advantages from both TiO2 and Fe3O4
individual components Most importantly even at
high current densities the FTHs still exhibits good
cyclic capacity retention and it is able to deliver a
reversible capacity as high as 1878 mAh g-1 even
after 400 cycles at a current density of 1 A g-1 The
reversible capacity is maintained at 1343 mAh g-1
when the current density is increased to 2 A g-1 Even
at the very high current density of 3 A g-1 the
reversible capacity still higher than 1122 mAh g-1
(Fig 3(d)) On the contrary such high current density
results in the very lower reversible capacity of 92
mAh g-1 for bare TiO2 nanofibers (Fig S5(a) in the
ESM) and severe capacity fading (decrease to 128
mAh g-1 only after 50 cycles) (Fig S5(b) in the ESM)
It is obvious that FTHs demonstrate superior cyclic
capacity retention over the bare TiO2 nanofibers and
Fe3O4 nanoparticles counterpart thanks to the
synergistic effect Fig 3(e) shows the rate
performance of FTHs in comparison with that of
bare TiO2 nanofibers and Fe3O4 nanoparticles (Fig S6
in the ESM) At current densities of 02 04 06 2 4
and 6 A g-1 the reversible capacities of FTHs are 4814
3354 2978 1991 995 and 65 mAh g-1 respectively
which are about two times larger than that of bare
TiO2 electrode Most importantly when the current
density is reduced after the back and forth high rate
and 120 cycles measurement a discharge capacity of
3702 mAh g-1 can be recovered On the contrary the
Fe3O4 nanoparticles show bad rate performance
especially at high current density it shows scarcely
no capacity due to the large volume expansion and
severe particle aggregation which results in the
electrode pulverization capacity loss and poor
cycling stability
As a battery delivers high power large heat (the
so-called Joule effect) can be generated during the
chargedischarge process which would heat up the
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
| wwweditorialmanagercomnaredefaultasp
6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
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[26] Yang Z X Du G D Meng Q Guo Z P Yu X
B Chen Z X Guo T L Zeng R Dispersion of SnO2
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1834-1840
[27] Parka H Song T Han H Devadoss A Yuh J Choi
C Paik U SnO2 encapsulated TiO2 hollow nanofibers as
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Commun 2012 22 81-84
[28] Jeun J-H Park K-Y Kim D-H Kim W-S Kim
H-C Lee B-S Kim H Yu W-R Kang K Hong
S-H SnO2TiO2 double-shell nanotubes for a lithium ion
battery anode with excellent high rate cyclability
Nanoscale 2013 5 8480-8483
[29] Nam S H Shim H S Kim Y S Dar M A Kim J G
Kim W B Ag or Au nanoparticle-embedded
one-dimensional composite TiO2 nanofibers prepared via
electrospinning for use in lithium-ion batteries ACS Appl
Mater Interface 2010 2 2046-2052
[30] He B L Dong B Li H L Preparation and
electrochemical properties of Ag-modified TiO2 nanotube
anode material for lithium-ion battery Electrochem
Commun 2007 9 425-430
[31] Taberna P L Mitra S Poizot P Simon P Tarascon J
M High rate capabilities Fe3O4-based Cu
nano-architectured electrodes for lithium-ion battery
applications Nat Mater 2006 5 567-573
[32] Zhang W M Wu X L Hu J S Guo Y G Wan L J
Carbon coated Fe3O4 nanospindles as a superior anode
material for lithium-ion batteries Adv Funct Mater 2008
18 3941-3946
[33] Zhu T Chen J S Lou X W Glucose-assisted one-pot
synthesis of FeOOH nanorods and their transformation to
Fe3O4carbon nanorods for application in lithium ion
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[34] Wu Y Wei Y Wang J P Jiang K L Fan S S
Conformal Fe3O4 sheath on aligned carbon nanotube
scaffolds as high-performance anodes for lithium ion
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[35] Lv P P Zhao H L Zeng Z P Wang J Zhang T H
Li X W Facile preparation and electrochemical properties
of carbon coated Fe3O4 as anode material for lithium-ion
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[36] Ito S Nakaoko K Kawamura M Ui K Fujimoto K
Koura N Lithium battery having a large capacity using
Fe3O4 as a cathode material J Power Sources 2005 146
319-322
[37] Mitra S Poizot P Finke A Tarascon J M Growth and
electrochemical characterization versus lithium of Fe3O4
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2006 16 2281-2287
[38] Liu H Wang G Wang J Wexler D Magnetitecarbon
core-shell nanorods as anode materials for lithium-ion
batteries Electrochem Commun 2008 10 1879-1882
[39] Zhou G Wang D W Li F Zhang L Li N Wu Z S
Wen L Lu G Q Cheng H M Graphene-wrapped Fe3O4
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8 Nano Res
anode material with improved reversible capacity and
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22 5306-5313
[40] Choi S H Son J W Yoon Y S Kim J Particle size
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[41] Masarapu C Zeng H F Hung K H Wei B Q Effect
of temperature on the capacitance of carbon nanotube
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[42] Yan J Sumboja A Khoo E Lee P S V2O5 loaded on
SnO2 nanowires for high-rate Li ion batteries Adv Mater
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[43] Zhou W W Cheng C W Liu J P Tay Y Y Jiang J
Jia X T Zhang J X Gong H Hng H H Yu T Fan
H J Epitaxial growth of branched α-Fe2O3SnO2
nano-heterostructures with improved lithium-ion battery
performance Adv Funct Mater 2011 21 2439-2445
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
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10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
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Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
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Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
TABLE OF CONTENTS (TOC)
Fe3O4 nanoparticle-decorated TiO2
nanofiber hierarchical heterostructures
with improved lithium-ion battery
performance over a wide temperature
range
Heng-guo Wang Guang-sheng Wang
Shuang Yuan De-long Ma Yang Li and
Yu Zhang
Beihang University China
Fe3O4 nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures are fabricated
by combining the electrospinning technique with the hydrothermal method and the
resulting materials show improved lithium-ion battery performance over a wide
temperature range due to the synergistic effect of binary composition as well as the
unique feature of the hierarchical nanofibers
Provide the authorsrsquo webside if possible
Author 1 webside 1
Author 2 webside 2
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Received day month year
Revised day month year
Accepted day month year
(automatically inserted by
the publisher)
copy Tsinghua University Press
and Springer-Verlag Berlin
Heidelberg 2014
KEYWORDS
hierarchical
heterostructures wide
temperature range
Improved performance
lithium-ion batteries
ABSTRACT
A facile strategy was designed for the fabrication of Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures (FTHs)
through combining the versatility of the electrospinning technique and
hydrothermal growth method Hierarchical architecture of Fe3O4 nanoparticle
decorated on TiO2 nanofiber is designed for the successful integration of binary
components to address the structural stability and low capacity In the resulted
unique architecture of FTHs the 1D heterostructures relieve the strain caused
by severe volume change of Fe3O4 during the numerous charge-discharge
cycles and thus suppress the degradation of the electrode material As a result
FTHs show excellent performance including higher reversible capacity
excellent cycle life and good rate performance at wide temperature range due
to the synergistic effect of binary composition of TiO2 and Fe3O4 as well as the
unique feature of the hierarchical nanofibers
1 Instruction
In recent years rechargeable lithium-ion batteries
(LIBs) successfully capture the portable electronic
market because they have been considered as an
effective and green electrochemical energy storage
device However graphite the most commonly used
anode material in commercial LIBs have limited
theoretical capacity (372 mAh g-1) due to their
intercalation mechanism which is far from adequate
to meet the upcoming markets of electric
transportation and renewable energies There is a
general consensus that the breakthrough of energy
density necessarily requires passage from classical
intercalation reactions to conversion reactions [1-2]
Nano Research
DOI (automatically inserted by the publisher)
Address correspondence to Yu Zhang email jadebuaaeducn
Review ArticleResearch Article Please choose one
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2 Nano Res
However even after decade of intensive efforts the
application of conversion-based materials is still
seriously hampered by the terrible capacity
degradation and poor rate performance Therefore
there is highly desirable to simultaneously improve
cyclic life energy- and power- density of LIBs
Transition metal oxides (TMOs) are very
promising conversion-based anode materials which
exhibit many attractive advantages of low cost
environmental friendliness natural abundance and
especially much higher theoretical capacity (500-1000
mAh g-1) greatly spurring the rapid development of
this field [3-13] However TMOs still suffer from
poor cyclability that is associated with the severe
agglomerations and large volume change during
charge-discharge Alternatively TiO2 has been
investigated intensively because of its robustness in
cycle retention and chemical stability [14-17] The
very low volume change of less than 4 during Li+
insertionextraction intrinsically endows TiO2 the
enhanced structural stability and prolonged cycle life
[18-21] However the low theoretical capacity (168
mAh g-1) and the poor rate capability of TiO2 still
seriously hinder its widespread use in LIBs
Recently various metal oxidesTiO2
nanocomposites especially with one-dimensional
(1D) nanostructures have been suggested to
overcome the demerits of both materials thus
improving the anode performance in LIBs such as
MoO2TiO2 [22] Fe2O3TiO2 [2324] CoOTiO2 [25]
SnO2TiO2 [26-28] Also we have demonstrated the
successful integration of individual components into
the unique nanostructures could endow the
composite electrode materials with the improved LIB
performance [25] On one hand the presence of TiO2
stem can effectively maintain the mechanical
integrity of electrode materials during Li+
insertionextraction ions On the other hand not only
coating with metal oxides overcomes the high cost of
coating with noble metals (Au Ag etc) [2930] but
also the low specific capacity of TiO2 can be
compensated by the electroactive metal oxides with
high capacity However some rare transition metal
oxides are not suitable to be used for electrode
materials in the case of large-scale energy storage
from a viewpoint of the sustainability Fe-based
oxides otherwise are more earth-abundant low cost
and environmental friendliness Among these
Fe-based oxides Fe3O4 features both high capacity
and high electronic conductivity [31-39] thus its
coating on TiO2 nanofibers could be killing three
birds with one stone - the rate performance and
specific capacity of TiO2 nanofibers and the cycle life
of Fe3O4 nanoparticles could be simultaneously
improved by the synergistic effect between Fe3O4 and
TiO2 This inspires us to design Fe3O4TiO2 composite
materials to investigate the synergistic effect of
binary composition and the unique nanostructures
thus preparing anode materials with improved LIB
performance
Herein Fe3O4 nanoparticle-decorated TiO2
nanofiber hierarchical heterostructures (FTHs) were
prepared by combining the electrospinning and the
hydrothermal method TiO2 nanofiber is chosen as
stems to induce the growth of heterostructured Fe3O4
nanoparticle Interestingly the TiO2 stem could
maintain the structural integrity and the sufficient
interspaces between Fe3O4 nanoparticles could
accommodate the volume expansion of Fe3O4 during
chargedischarge process So when FTHs are tested
as anode materials for LIBs it shows excellent
performance including higher reversible capacity
excellent cycle life and good rate performance at
wide temperature range due to the synergistic effect
of binary composition of TiO2 and Fe3O4 as well as
the unique feature of the hierarchical nanofibers
2 Experimental
21 Synthesis of FTHs
The hierarchical Fe3O4TiO2 nanofibers were
synthesized by the electrospinning technique and
hydrothermal method [25] In a typical process
electrospun TiO2 nanofibers (20 mg) were put into
Teflon-lined autoclave (50 mL) with a ethylene glycol
(EG 25 mL) solution consisting of FeCl3middot6H2O (025 g)
polyethylene glycol (PEG 025 g) and sodium
acetate (NaAc 09 g) After the autoclave was sealed
and heated at 200 for 16 h the as-obtained
composite was collected out washed with ethanol
and deionized water respectively and then dried
under vacuum at 50 for 12 h For comparison the
TiO2Fe3O4 nanofibers with few secondary Fe3O4
nanoparticles (FTHfs) were also prepared by adding
FeCl3middot6H2O (005 g) and the free Fe3O4 nanoparticles
were also prepared without the addition of TiO2
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3 Nano Res
nanofibers
22 Characterization
Scanning electron microscopy (SEM) images were
collected with a Hitachi S-4800 instrument
Transmission electron microscope (TEM) images
were carried out with a Tecnai G2 using 200 kV X-ray
diffraction (XRD) patterns were carried out with a
Rigaku-Dmax 2500 diffractometer using Cu Kα
radiation X-ray photoelectron spectroscopy (XPS)
analysis was conducted with ESCALAB MK II X-ray
instrument
23 Electrochemical Evaluation
70 wt active materials (FTHs FTHfs TiO2
nanofibers Fe3O4 nanoparticles and TiO2-Fe3O4
mixture) 20 wt acetylene black and 10 wt
polyvinylidene fluoride (PVDF) were mixed in
N-methyl-2-pyrrolidone (NMP) and then uniformly
pasted on copper foil After finally dried in vacuum
at 80 for 12 h to remove the solvent the work
electrodes were pressed and cut into disks Thin
lithium foil was used as the counter electrode
Celgard 2400 membrane was used as separator and
lithium hexafluorophosphate LiPF6 (1 M) in ethylene
carbonatedimethyl carbonate (ECDMC 11 vol )
was employed as the electrolyte Galvanostatic
chargedischarge experiments were conducted in a
voltage range of 001-30 V with a Land Battery
Measurement System (Land China) The cyclic
voltammetry (CV 001-3 V 01 mV s-1) and
electrochemical impedance spectroscopy (EIS 01-700
kHz 5 mV) were conducted using a VMP3
Electrochemical Workstation (Bio-logic Inc)
3 Results and discussion
Scheme 1 illustrates the overall synthesis procedure
employed for the preparation of FTHs which is
briefly composed of the electrospinning and the
hydrothermal method Herein no surface
pretreatments are needed to introduce new surface
functional groups or additional covalent andor
noncovalent interconnectivity As a result perfectly
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures were obtained in high
yield The morphology of the prepared samples is
characterized by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) Fig 1(a)
and 1(b) show SEM images of bare TiO2 nanofibers
and FTHs The bare TiO2 non-woven nanofibers with
average diameter about 220 nm (Fig 1(a) inset) have
a relatively smooth surface The resulting materials
show hierarchical nanostructure and have diameters
of about 250 nm (Fig 1(b) inset) From TEM image in
Fig 1(c) it is obvious that the secondary Fe3O4
nanoparticles grow on the surface of TiO2 nanofibers
From the High-resolution transmission electron
microscopy (HRTEM) image of the heterojunction
region (Fig 1(d)) the observed two set of lattice
fringe spacings of 035 and 0254 nm are consistent
with the (101) plane of the anatase crystal structure of
TiO2 and the (311) plane of the cubic magnetite Fe3O4
respectively From the HRTEM image (Fig 1(e)) of
the nanoparticle it is also concluded that the
secondary Fe3O4 nanoparticles successfully grow on
the surface of the TiO2 nanofibers Furthermore
energy-dispersive X-ray spectroscopy (EDS)
characterization (Fig S1 in the Electronic
Supplementary Material (ESM)) also confirms that
FTHs include Fe Ti and O indicating the presence
of both Fe3O4 and TiO2 And EDS line scanning along
the cross section of FTHs (Fig 1(f)) further shows
that Fe is present only outside the TiO2 nanofibers
but not inside As a result Fe3O4
nanoparticle-decorated TiO2 nanofiber results in the
formation of the hierarchical Fe3O4TiO2 coreshell
nanofibers Moreover the thicknesses of the
secondary Fe3O4 nanoparticles are controllable by
simply changing the experimental parameters (Fig
S2 in the ESM)
The crystallographic structure of the prepared
samples is investigated by powder X-ray diffraction
(XRD) As shown in Fig 2(a) all the diffraction peaks
could be indexed to anatase TiO2 (JCPDS file No
21-1272) and cubic magnetite Fe3O4 (JCPDS file No
19-0629) X-ray photoelectron spectroscopy (XPS)
characterization is further carried out to analyze the
elemental composition As shown in Fig 2(b) the
XPS spectrum of FTHs shows the presence of the
Ti2p O1s and Fe2p peak For the high-resolution
Fe2p (Fig 2(b) inset) it is observed that two peaks of
Fe2p32 and Fe2p12 appear at 711 and 724 eV
respectively which demonstrates the secondary
nanostructures are Fe3O4 Then inductively coupled
plasma atomic emission spectrometry (ICP-AES) is
also carried out to test the actual iron contents in
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4 Nano Res
each sample The results show that the iron contents
are 140 and 182 wt in FTHs with few secondary
Fe3O4 nanoparticles (FTHfs) and FTHs respectively
The electrochemical performance of FTHs is
investigated as anode materials for LIBs Fig 3(a)
shows its cyclic voltammetry (CV) curves Two pairs
of redox current peaks can be clearly identified
during the cathodic and anodic scans In the first
cycle two current peaks appear at ~175 and ~21 V
respectively which can be regarded as the signature
of the lithium insertionextraction processes in the
anatase framework In addition the sharp reduction
peak at ~07 V can be ascribed to the conversion of
Fe3O4 to Fe and the formation of amorphous Li2O as
well as their irreversible reaction with the electrolyte
which may lead to the irreversible capacity At the
same time the wide oxidation peak at ~17 V could
be assigned to the reversible oxidation of Fe0 to Fe3+
during the anodic process [3839] For comparison
bare TiO2 nanofibers and Fe3O4 nanoparticles are also
tested The two pairs of well-shaped redox peaks for
TiO2 nanofibers (Fig S3(a) in the ESM) and Fe3O4
nanoparticles (Fig S3(b) in the ESM) are in good
agreement with those for FTHs Note that as
expected there is only a slight decrease in the peak
current during the subsequent cycles for TiO2
nanofibers indicating the highly reversible redox
reactions of TiO2 nanofibers In contrast the peak
current of the redox peaks of Fe3O4 nanoparticles
drops dramatically during the subsequent scans
indicating seriously irreversible reactions have taken
place in the Fe3O4 electrode thus leading to a severe
capacity fading upon charge-discharge cycling
Therefore we anticipate the reinforcement of Fe3O4
nanoparticles by stable TiO2 nanofibers can
effectively alleviate the severe capacity fading
Fig 3(b) shows the discharge-charge curves of
FTHs at 100 mA g-1 Consistent with the above CV
analysis two discharge plateaus at ~175 and 07 V
and two charge plateaus at ~17 and 21 V can be
clearly observed These voltage profiles are
characteristic of both Fe3O4-based and TiO2-based
materials The initial discharge and charge capacities
are found to be 7836 and 4945 mAh g-1 respectively
corresponding to a Coulombic efficiency of 631
Furthermore in the successive cycles the capacity of
the electrode scarcely decays and it can still deliver a
reversible capacity of 4545 mAh g-1 even after 200
cycles (Fig 3(b) and 3(c)) On the contrary the bare
TiO2 nanofibers electrode only exhibits a lower
reversible capacity of 202 mAh g-1 (Fig S4(a) in the
ESM) Although the Fe3O4 nanoparticles exhibits
higher initial discharge capacity of 10634 mAh g-1
(Fig S4(b) in the ESM) it suffers severe capacity
fading (decrease to 1577 mAh g-1 only after 70 cycles)
(Fig S4(c) in the ESM) which is lower than that of
FTHs indicating that the successful integration of
binary TiO2-Fe3O4 components can favourably inherit
the respective advantages from both TiO2 and Fe3O4
individual components Most importantly even at
high current densities the FTHs still exhibits good
cyclic capacity retention and it is able to deliver a
reversible capacity as high as 1878 mAh g-1 even
after 400 cycles at a current density of 1 A g-1 The
reversible capacity is maintained at 1343 mAh g-1
when the current density is increased to 2 A g-1 Even
at the very high current density of 3 A g-1 the
reversible capacity still higher than 1122 mAh g-1
(Fig 3(d)) On the contrary such high current density
results in the very lower reversible capacity of 92
mAh g-1 for bare TiO2 nanofibers (Fig S5(a) in the
ESM) and severe capacity fading (decrease to 128
mAh g-1 only after 50 cycles) (Fig S5(b) in the ESM)
It is obvious that FTHs demonstrate superior cyclic
capacity retention over the bare TiO2 nanofibers and
Fe3O4 nanoparticles counterpart thanks to the
synergistic effect Fig 3(e) shows the rate
performance of FTHs in comparison with that of
bare TiO2 nanofibers and Fe3O4 nanoparticles (Fig S6
in the ESM) At current densities of 02 04 06 2 4
and 6 A g-1 the reversible capacities of FTHs are 4814
3354 2978 1991 995 and 65 mAh g-1 respectively
which are about two times larger than that of bare
TiO2 electrode Most importantly when the current
density is reduced after the back and forth high rate
and 120 cycles measurement a discharge capacity of
3702 mAh g-1 can be recovered On the contrary the
Fe3O4 nanoparticles show bad rate performance
especially at high current density it shows scarcely
no capacity due to the large volume expansion and
severe particle aggregation which results in the
electrode pulverization capacity loss and poor
cycling stability
As a battery delivers high power large heat (the
so-called Joule effect) can be generated during the
chargedischarge process which would heat up the
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5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
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6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
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8 Nano Res
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wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
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10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
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Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
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Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Received day month year
Revised day month year
Accepted day month year
(automatically inserted by
the publisher)
copy Tsinghua University Press
and Springer-Verlag Berlin
Heidelberg 2014
KEYWORDS
hierarchical
heterostructures wide
temperature range
Improved performance
lithium-ion batteries
ABSTRACT
A facile strategy was designed for the fabrication of Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures (FTHs)
through combining the versatility of the electrospinning technique and
hydrothermal growth method Hierarchical architecture of Fe3O4 nanoparticle
decorated on TiO2 nanofiber is designed for the successful integration of binary
components to address the structural stability and low capacity In the resulted
unique architecture of FTHs the 1D heterostructures relieve the strain caused
by severe volume change of Fe3O4 during the numerous charge-discharge
cycles and thus suppress the degradation of the electrode material As a result
FTHs show excellent performance including higher reversible capacity
excellent cycle life and good rate performance at wide temperature range due
to the synergistic effect of binary composition of TiO2 and Fe3O4 as well as the
unique feature of the hierarchical nanofibers
1 Instruction
In recent years rechargeable lithium-ion batteries
(LIBs) successfully capture the portable electronic
market because they have been considered as an
effective and green electrochemical energy storage
device However graphite the most commonly used
anode material in commercial LIBs have limited
theoretical capacity (372 mAh g-1) due to their
intercalation mechanism which is far from adequate
to meet the upcoming markets of electric
transportation and renewable energies There is a
general consensus that the breakthrough of energy
density necessarily requires passage from classical
intercalation reactions to conversion reactions [1-2]
Nano Research
DOI (automatically inserted by the publisher)
Address correspondence to Yu Zhang email jadebuaaeducn
Review ArticleResearch Article Please choose one
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2 Nano Res
However even after decade of intensive efforts the
application of conversion-based materials is still
seriously hampered by the terrible capacity
degradation and poor rate performance Therefore
there is highly desirable to simultaneously improve
cyclic life energy- and power- density of LIBs
Transition metal oxides (TMOs) are very
promising conversion-based anode materials which
exhibit many attractive advantages of low cost
environmental friendliness natural abundance and
especially much higher theoretical capacity (500-1000
mAh g-1) greatly spurring the rapid development of
this field [3-13] However TMOs still suffer from
poor cyclability that is associated with the severe
agglomerations and large volume change during
charge-discharge Alternatively TiO2 has been
investigated intensively because of its robustness in
cycle retention and chemical stability [14-17] The
very low volume change of less than 4 during Li+
insertionextraction intrinsically endows TiO2 the
enhanced structural stability and prolonged cycle life
[18-21] However the low theoretical capacity (168
mAh g-1) and the poor rate capability of TiO2 still
seriously hinder its widespread use in LIBs
Recently various metal oxidesTiO2
nanocomposites especially with one-dimensional
(1D) nanostructures have been suggested to
overcome the demerits of both materials thus
improving the anode performance in LIBs such as
MoO2TiO2 [22] Fe2O3TiO2 [2324] CoOTiO2 [25]
SnO2TiO2 [26-28] Also we have demonstrated the
successful integration of individual components into
the unique nanostructures could endow the
composite electrode materials with the improved LIB
performance [25] On one hand the presence of TiO2
stem can effectively maintain the mechanical
integrity of electrode materials during Li+
insertionextraction ions On the other hand not only
coating with metal oxides overcomes the high cost of
coating with noble metals (Au Ag etc) [2930] but
also the low specific capacity of TiO2 can be
compensated by the electroactive metal oxides with
high capacity However some rare transition metal
oxides are not suitable to be used for electrode
materials in the case of large-scale energy storage
from a viewpoint of the sustainability Fe-based
oxides otherwise are more earth-abundant low cost
and environmental friendliness Among these
Fe-based oxides Fe3O4 features both high capacity
and high electronic conductivity [31-39] thus its
coating on TiO2 nanofibers could be killing three
birds with one stone - the rate performance and
specific capacity of TiO2 nanofibers and the cycle life
of Fe3O4 nanoparticles could be simultaneously
improved by the synergistic effect between Fe3O4 and
TiO2 This inspires us to design Fe3O4TiO2 composite
materials to investigate the synergistic effect of
binary composition and the unique nanostructures
thus preparing anode materials with improved LIB
performance
Herein Fe3O4 nanoparticle-decorated TiO2
nanofiber hierarchical heterostructures (FTHs) were
prepared by combining the electrospinning and the
hydrothermal method TiO2 nanofiber is chosen as
stems to induce the growth of heterostructured Fe3O4
nanoparticle Interestingly the TiO2 stem could
maintain the structural integrity and the sufficient
interspaces between Fe3O4 nanoparticles could
accommodate the volume expansion of Fe3O4 during
chargedischarge process So when FTHs are tested
as anode materials for LIBs it shows excellent
performance including higher reversible capacity
excellent cycle life and good rate performance at
wide temperature range due to the synergistic effect
of binary composition of TiO2 and Fe3O4 as well as
the unique feature of the hierarchical nanofibers
2 Experimental
21 Synthesis of FTHs
The hierarchical Fe3O4TiO2 nanofibers were
synthesized by the electrospinning technique and
hydrothermal method [25] In a typical process
electrospun TiO2 nanofibers (20 mg) were put into
Teflon-lined autoclave (50 mL) with a ethylene glycol
(EG 25 mL) solution consisting of FeCl3middot6H2O (025 g)
polyethylene glycol (PEG 025 g) and sodium
acetate (NaAc 09 g) After the autoclave was sealed
and heated at 200 for 16 h the as-obtained
composite was collected out washed with ethanol
and deionized water respectively and then dried
under vacuum at 50 for 12 h For comparison the
TiO2Fe3O4 nanofibers with few secondary Fe3O4
nanoparticles (FTHfs) were also prepared by adding
FeCl3middot6H2O (005 g) and the free Fe3O4 nanoparticles
were also prepared without the addition of TiO2
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3 Nano Res
nanofibers
22 Characterization
Scanning electron microscopy (SEM) images were
collected with a Hitachi S-4800 instrument
Transmission electron microscope (TEM) images
were carried out with a Tecnai G2 using 200 kV X-ray
diffraction (XRD) patterns were carried out with a
Rigaku-Dmax 2500 diffractometer using Cu Kα
radiation X-ray photoelectron spectroscopy (XPS)
analysis was conducted with ESCALAB MK II X-ray
instrument
23 Electrochemical Evaluation
70 wt active materials (FTHs FTHfs TiO2
nanofibers Fe3O4 nanoparticles and TiO2-Fe3O4
mixture) 20 wt acetylene black and 10 wt
polyvinylidene fluoride (PVDF) were mixed in
N-methyl-2-pyrrolidone (NMP) and then uniformly
pasted on copper foil After finally dried in vacuum
at 80 for 12 h to remove the solvent the work
electrodes were pressed and cut into disks Thin
lithium foil was used as the counter electrode
Celgard 2400 membrane was used as separator and
lithium hexafluorophosphate LiPF6 (1 M) in ethylene
carbonatedimethyl carbonate (ECDMC 11 vol )
was employed as the electrolyte Galvanostatic
chargedischarge experiments were conducted in a
voltage range of 001-30 V with a Land Battery
Measurement System (Land China) The cyclic
voltammetry (CV 001-3 V 01 mV s-1) and
electrochemical impedance spectroscopy (EIS 01-700
kHz 5 mV) were conducted using a VMP3
Electrochemical Workstation (Bio-logic Inc)
3 Results and discussion
Scheme 1 illustrates the overall synthesis procedure
employed for the preparation of FTHs which is
briefly composed of the electrospinning and the
hydrothermal method Herein no surface
pretreatments are needed to introduce new surface
functional groups or additional covalent andor
noncovalent interconnectivity As a result perfectly
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures were obtained in high
yield The morphology of the prepared samples is
characterized by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) Fig 1(a)
and 1(b) show SEM images of bare TiO2 nanofibers
and FTHs The bare TiO2 non-woven nanofibers with
average diameter about 220 nm (Fig 1(a) inset) have
a relatively smooth surface The resulting materials
show hierarchical nanostructure and have diameters
of about 250 nm (Fig 1(b) inset) From TEM image in
Fig 1(c) it is obvious that the secondary Fe3O4
nanoparticles grow on the surface of TiO2 nanofibers
From the High-resolution transmission electron
microscopy (HRTEM) image of the heterojunction
region (Fig 1(d)) the observed two set of lattice
fringe spacings of 035 and 0254 nm are consistent
with the (101) plane of the anatase crystal structure of
TiO2 and the (311) plane of the cubic magnetite Fe3O4
respectively From the HRTEM image (Fig 1(e)) of
the nanoparticle it is also concluded that the
secondary Fe3O4 nanoparticles successfully grow on
the surface of the TiO2 nanofibers Furthermore
energy-dispersive X-ray spectroscopy (EDS)
characterization (Fig S1 in the Electronic
Supplementary Material (ESM)) also confirms that
FTHs include Fe Ti and O indicating the presence
of both Fe3O4 and TiO2 And EDS line scanning along
the cross section of FTHs (Fig 1(f)) further shows
that Fe is present only outside the TiO2 nanofibers
but not inside As a result Fe3O4
nanoparticle-decorated TiO2 nanofiber results in the
formation of the hierarchical Fe3O4TiO2 coreshell
nanofibers Moreover the thicknesses of the
secondary Fe3O4 nanoparticles are controllable by
simply changing the experimental parameters (Fig
S2 in the ESM)
The crystallographic structure of the prepared
samples is investigated by powder X-ray diffraction
(XRD) As shown in Fig 2(a) all the diffraction peaks
could be indexed to anatase TiO2 (JCPDS file No
21-1272) and cubic magnetite Fe3O4 (JCPDS file No
19-0629) X-ray photoelectron spectroscopy (XPS)
characterization is further carried out to analyze the
elemental composition As shown in Fig 2(b) the
XPS spectrum of FTHs shows the presence of the
Ti2p O1s and Fe2p peak For the high-resolution
Fe2p (Fig 2(b) inset) it is observed that two peaks of
Fe2p32 and Fe2p12 appear at 711 and 724 eV
respectively which demonstrates the secondary
nanostructures are Fe3O4 Then inductively coupled
plasma atomic emission spectrometry (ICP-AES) is
also carried out to test the actual iron contents in
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4 Nano Res
each sample The results show that the iron contents
are 140 and 182 wt in FTHs with few secondary
Fe3O4 nanoparticles (FTHfs) and FTHs respectively
The electrochemical performance of FTHs is
investigated as anode materials for LIBs Fig 3(a)
shows its cyclic voltammetry (CV) curves Two pairs
of redox current peaks can be clearly identified
during the cathodic and anodic scans In the first
cycle two current peaks appear at ~175 and ~21 V
respectively which can be regarded as the signature
of the lithium insertionextraction processes in the
anatase framework In addition the sharp reduction
peak at ~07 V can be ascribed to the conversion of
Fe3O4 to Fe and the formation of amorphous Li2O as
well as their irreversible reaction with the electrolyte
which may lead to the irreversible capacity At the
same time the wide oxidation peak at ~17 V could
be assigned to the reversible oxidation of Fe0 to Fe3+
during the anodic process [3839] For comparison
bare TiO2 nanofibers and Fe3O4 nanoparticles are also
tested The two pairs of well-shaped redox peaks for
TiO2 nanofibers (Fig S3(a) in the ESM) and Fe3O4
nanoparticles (Fig S3(b) in the ESM) are in good
agreement with those for FTHs Note that as
expected there is only a slight decrease in the peak
current during the subsequent cycles for TiO2
nanofibers indicating the highly reversible redox
reactions of TiO2 nanofibers In contrast the peak
current of the redox peaks of Fe3O4 nanoparticles
drops dramatically during the subsequent scans
indicating seriously irreversible reactions have taken
place in the Fe3O4 electrode thus leading to a severe
capacity fading upon charge-discharge cycling
Therefore we anticipate the reinforcement of Fe3O4
nanoparticles by stable TiO2 nanofibers can
effectively alleviate the severe capacity fading
Fig 3(b) shows the discharge-charge curves of
FTHs at 100 mA g-1 Consistent with the above CV
analysis two discharge plateaus at ~175 and 07 V
and two charge plateaus at ~17 and 21 V can be
clearly observed These voltage profiles are
characteristic of both Fe3O4-based and TiO2-based
materials The initial discharge and charge capacities
are found to be 7836 and 4945 mAh g-1 respectively
corresponding to a Coulombic efficiency of 631
Furthermore in the successive cycles the capacity of
the electrode scarcely decays and it can still deliver a
reversible capacity of 4545 mAh g-1 even after 200
cycles (Fig 3(b) and 3(c)) On the contrary the bare
TiO2 nanofibers electrode only exhibits a lower
reversible capacity of 202 mAh g-1 (Fig S4(a) in the
ESM) Although the Fe3O4 nanoparticles exhibits
higher initial discharge capacity of 10634 mAh g-1
(Fig S4(b) in the ESM) it suffers severe capacity
fading (decrease to 1577 mAh g-1 only after 70 cycles)
(Fig S4(c) in the ESM) which is lower than that of
FTHs indicating that the successful integration of
binary TiO2-Fe3O4 components can favourably inherit
the respective advantages from both TiO2 and Fe3O4
individual components Most importantly even at
high current densities the FTHs still exhibits good
cyclic capacity retention and it is able to deliver a
reversible capacity as high as 1878 mAh g-1 even
after 400 cycles at a current density of 1 A g-1 The
reversible capacity is maintained at 1343 mAh g-1
when the current density is increased to 2 A g-1 Even
at the very high current density of 3 A g-1 the
reversible capacity still higher than 1122 mAh g-1
(Fig 3(d)) On the contrary such high current density
results in the very lower reversible capacity of 92
mAh g-1 for bare TiO2 nanofibers (Fig S5(a) in the
ESM) and severe capacity fading (decrease to 128
mAh g-1 only after 50 cycles) (Fig S5(b) in the ESM)
It is obvious that FTHs demonstrate superior cyclic
capacity retention over the bare TiO2 nanofibers and
Fe3O4 nanoparticles counterpart thanks to the
synergistic effect Fig 3(e) shows the rate
performance of FTHs in comparison with that of
bare TiO2 nanofibers and Fe3O4 nanoparticles (Fig S6
in the ESM) At current densities of 02 04 06 2 4
and 6 A g-1 the reversible capacities of FTHs are 4814
3354 2978 1991 995 and 65 mAh g-1 respectively
which are about two times larger than that of bare
TiO2 electrode Most importantly when the current
density is reduced after the back and forth high rate
and 120 cycles measurement a discharge capacity of
3702 mAh g-1 can be recovered On the contrary the
Fe3O4 nanoparticles show bad rate performance
especially at high current density it shows scarcely
no capacity due to the large volume expansion and
severe particle aggregation which results in the
electrode pulverization capacity loss and poor
cycling stability
As a battery delivers high power large heat (the
so-called Joule effect) can be generated during the
chargedischarge process which would heat up the
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5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
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6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
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8 Nano Res
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wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
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10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
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Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
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Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
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Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
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2 Nano Res
However even after decade of intensive efforts the
application of conversion-based materials is still
seriously hampered by the terrible capacity
degradation and poor rate performance Therefore
there is highly desirable to simultaneously improve
cyclic life energy- and power- density of LIBs
Transition metal oxides (TMOs) are very
promising conversion-based anode materials which
exhibit many attractive advantages of low cost
environmental friendliness natural abundance and
especially much higher theoretical capacity (500-1000
mAh g-1) greatly spurring the rapid development of
this field [3-13] However TMOs still suffer from
poor cyclability that is associated with the severe
agglomerations and large volume change during
charge-discharge Alternatively TiO2 has been
investigated intensively because of its robustness in
cycle retention and chemical stability [14-17] The
very low volume change of less than 4 during Li+
insertionextraction intrinsically endows TiO2 the
enhanced structural stability and prolonged cycle life
[18-21] However the low theoretical capacity (168
mAh g-1) and the poor rate capability of TiO2 still
seriously hinder its widespread use in LIBs
Recently various metal oxidesTiO2
nanocomposites especially with one-dimensional
(1D) nanostructures have been suggested to
overcome the demerits of both materials thus
improving the anode performance in LIBs such as
MoO2TiO2 [22] Fe2O3TiO2 [2324] CoOTiO2 [25]
SnO2TiO2 [26-28] Also we have demonstrated the
successful integration of individual components into
the unique nanostructures could endow the
composite electrode materials with the improved LIB
performance [25] On one hand the presence of TiO2
stem can effectively maintain the mechanical
integrity of electrode materials during Li+
insertionextraction ions On the other hand not only
coating with metal oxides overcomes the high cost of
coating with noble metals (Au Ag etc) [2930] but
also the low specific capacity of TiO2 can be
compensated by the electroactive metal oxides with
high capacity However some rare transition metal
oxides are not suitable to be used for electrode
materials in the case of large-scale energy storage
from a viewpoint of the sustainability Fe-based
oxides otherwise are more earth-abundant low cost
and environmental friendliness Among these
Fe-based oxides Fe3O4 features both high capacity
and high electronic conductivity [31-39] thus its
coating on TiO2 nanofibers could be killing three
birds with one stone - the rate performance and
specific capacity of TiO2 nanofibers and the cycle life
of Fe3O4 nanoparticles could be simultaneously
improved by the synergistic effect between Fe3O4 and
TiO2 This inspires us to design Fe3O4TiO2 composite
materials to investigate the synergistic effect of
binary composition and the unique nanostructures
thus preparing anode materials with improved LIB
performance
Herein Fe3O4 nanoparticle-decorated TiO2
nanofiber hierarchical heterostructures (FTHs) were
prepared by combining the electrospinning and the
hydrothermal method TiO2 nanofiber is chosen as
stems to induce the growth of heterostructured Fe3O4
nanoparticle Interestingly the TiO2 stem could
maintain the structural integrity and the sufficient
interspaces between Fe3O4 nanoparticles could
accommodate the volume expansion of Fe3O4 during
chargedischarge process So when FTHs are tested
as anode materials for LIBs it shows excellent
performance including higher reversible capacity
excellent cycle life and good rate performance at
wide temperature range due to the synergistic effect
of binary composition of TiO2 and Fe3O4 as well as
the unique feature of the hierarchical nanofibers
2 Experimental
21 Synthesis of FTHs
The hierarchical Fe3O4TiO2 nanofibers were
synthesized by the electrospinning technique and
hydrothermal method [25] In a typical process
electrospun TiO2 nanofibers (20 mg) were put into
Teflon-lined autoclave (50 mL) with a ethylene glycol
(EG 25 mL) solution consisting of FeCl3middot6H2O (025 g)
polyethylene glycol (PEG 025 g) and sodium
acetate (NaAc 09 g) After the autoclave was sealed
and heated at 200 for 16 h the as-obtained
composite was collected out washed with ethanol
and deionized water respectively and then dried
under vacuum at 50 for 12 h For comparison the
TiO2Fe3O4 nanofibers with few secondary Fe3O4
nanoparticles (FTHfs) were also prepared by adding
FeCl3middot6H2O (005 g) and the free Fe3O4 nanoparticles
were also prepared without the addition of TiO2
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3 Nano Res
nanofibers
22 Characterization
Scanning electron microscopy (SEM) images were
collected with a Hitachi S-4800 instrument
Transmission electron microscope (TEM) images
were carried out with a Tecnai G2 using 200 kV X-ray
diffraction (XRD) patterns were carried out with a
Rigaku-Dmax 2500 diffractometer using Cu Kα
radiation X-ray photoelectron spectroscopy (XPS)
analysis was conducted with ESCALAB MK II X-ray
instrument
23 Electrochemical Evaluation
70 wt active materials (FTHs FTHfs TiO2
nanofibers Fe3O4 nanoparticles and TiO2-Fe3O4
mixture) 20 wt acetylene black and 10 wt
polyvinylidene fluoride (PVDF) were mixed in
N-methyl-2-pyrrolidone (NMP) and then uniformly
pasted on copper foil After finally dried in vacuum
at 80 for 12 h to remove the solvent the work
electrodes were pressed and cut into disks Thin
lithium foil was used as the counter electrode
Celgard 2400 membrane was used as separator and
lithium hexafluorophosphate LiPF6 (1 M) in ethylene
carbonatedimethyl carbonate (ECDMC 11 vol )
was employed as the electrolyte Galvanostatic
chargedischarge experiments were conducted in a
voltage range of 001-30 V with a Land Battery
Measurement System (Land China) The cyclic
voltammetry (CV 001-3 V 01 mV s-1) and
electrochemical impedance spectroscopy (EIS 01-700
kHz 5 mV) were conducted using a VMP3
Electrochemical Workstation (Bio-logic Inc)
3 Results and discussion
Scheme 1 illustrates the overall synthesis procedure
employed for the preparation of FTHs which is
briefly composed of the electrospinning and the
hydrothermal method Herein no surface
pretreatments are needed to introduce new surface
functional groups or additional covalent andor
noncovalent interconnectivity As a result perfectly
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures were obtained in high
yield The morphology of the prepared samples is
characterized by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) Fig 1(a)
and 1(b) show SEM images of bare TiO2 nanofibers
and FTHs The bare TiO2 non-woven nanofibers with
average diameter about 220 nm (Fig 1(a) inset) have
a relatively smooth surface The resulting materials
show hierarchical nanostructure and have diameters
of about 250 nm (Fig 1(b) inset) From TEM image in
Fig 1(c) it is obvious that the secondary Fe3O4
nanoparticles grow on the surface of TiO2 nanofibers
From the High-resolution transmission electron
microscopy (HRTEM) image of the heterojunction
region (Fig 1(d)) the observed two set of lattice
fringe spacings of 035 and 0254 nm are consistent
with the (101) plane of the anatase crystal structure of
TiO2 and the (311) plane of the cubic magnetite Fe3O4
respectively From the HRTEM image (Fig 1(e)) of
the nanoparticle it is also concluded that the
secondary Fe3O4 nanoparticles successfully grow on
the surface of the TiO2 nanofibers Furthermore
energy-dispersive X-ray spectroscopy (EDS)
characterization (Fig S1 in the Electronic
Supplementary Material (ESM)) also confirms that
FTHs include Fe Ti and O indicating the presence
of both Fe3O4 and TiO2 And EDS line scanning along
the cross section of FTHs (Fig 1(f)) further shows
that Fe is present only outside the TiO2 nanofibers
but not inside As a result Fe3O4
nanoparticle-decorated TiO2 nanofiber results in the
formation of the hierarchical Fe3O4TiO2 coreshell
nanofibers Moreover the thicknesses of the
secondary Fe3O4 nanoparticles are controllable by
simply changing the experimental parameters (Fig
S2 in the ESM)
The crystallographic structure of the prepared
samples is investigated by powder X-ray diffraction
(XRD) As shown in Fig 2(a) all the diffraction peaks
could be indexed to anatase TiO2 (JCPDS file No
21-1272) and cubic magnetite Fe3O4 (JCPDS file No
19-0629) X-ray photoelectron spectroscopy (XPS)
characterization is further carried out to analyze the
elemental composition As shown in Fig 2(b) the
XPS spectrum of FTHs shows the presence of the
Ti2p O1s and Fe2p peak For the high-resolution
Fe2p (Fig 2(b) inset) it is observed that two peaks of
Fe2p32 and Fe2p12 appear at 711 and 724 eV
respectively which demonstrates the secondary
nanostructures are Fe3O4 Then inductively coupled
plasma atomic emission spectrometry (ICP-AES) is
also carried out to test the actual iron contents in
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4 Nano Res
each sample The results show that the iron contents
are 140 and 182 wt in FTHs with few secondary
Fe3O4 nanoparticles (FTHfs) and FTHs respectively
The electrochemical performance of FTHs is
investigated as anode materials for LIBs Fig 3(a)
shows its cyclic voltammetry (CV) curves Two pairs
of redox current peaks can be clearly identified
during the cathodic and anodic scans In the first
cycle two current peaks appear at ~175 and ~21 V
respectively which can be regarded as the signature
of the lithium insertionextraction processes in the
anatase framework In addition the sharp reduction
peak at ~07 V can be ascribed to the conversion of
Fe3O4 to Fe and the formation of amorphous Li2O as
well as their irreversible reaction with the electrolyte
which may lead to the irreversible capacity At the
same time the wide oxidation peak at ~17 V could
be assigned to the reversible oxidation of Fe0 to Fe3+
during the anodic process [3839] For comparison
bare TiO2 nanofibers and Fe3O4 nanoparticles are also
tested The two pairs of well-shaped redox peaks for
TiO2 nanofibers (Fig S3(a) in the ESM) and Fe3O4
nanoparticles (Fig S3(b) in the ESM) are in good
agreement with those for FTHs Note that as
expected there is only a slight decrease in the peak
current during the subsequent cycles for TiO2
nanofibers indicating the highly reversible redox
reactions of TiO2 nanofibers In contrast the peak
current of the redox peaks of Fe3O4 nanoparticles
drops dramatically during the subsequent scans
indicating seriously irreversible reactions have taken
place in the Fe3O4 electrode thus leading to a severe
capacity fading upon charge-discharge cycling
Therefore we anticipate the reinforcement of Fe3O4
nanoparticles by stable TiO2 nanofibers can
effectively alleviate the severe capacity fading
Fig 3(b) shows the discharge-charge curves of
FTHs at 100 mA g-1 Consistent with the above CV
analysis two discharge plateaus at ~175 and 07 V
and two charge plateaus at ~17 and 21 V can be
clearly observed These voltage profiles are
characteristic of both Fe3O4-based and TiO2-based
materials The initial discharge and charge capacities
are found to be 7836 and 4945 mAh g-1 respectively
corresponding to a Coulombic efficiency of 631
Furthermore in the successive cycles the capacity of
the electrode scarcely decays and it can still deliver a
reversible capacity of 4545 mAh g-1 even after 200
cycles (Fig 3(b) and 3(c)) On the contrary the bare
TiO2 nanofibers electrode only exhibits a lower
reversible capacity of 202 mAh g-1 (Fig S4(a) in the
ESM) Although the Fe3O4 nanoparticles exhibits
higher initial discharge capacity of 10634 mAh g-1
(Fig S4(b) in the ESM) it suffers severe capacity
fading (decrease to 1577 mAh g-1 only after 70 cycles)
(Fig S4(c) in the ESM) which is lower than that of
FTHs indicating that the successful integration of
binary TiO2-Fe3O4 components can favourably inherit
the respective advantages from both TiO2 and Fe3O4
individual components Most importantly even at
high current densities the FTHs still exhibits good
cyclic capacity retention and it is able to deliver a
reversible capacity as high as 1878 mAh g-1 even
after 400 cycles at a current density of 1 A g-1 The
reversible capacity is maintained at 1343 mAh g-1
when the current density is increased to 2 A g-1 Even
at the very high current density of 3 A g-1 the
reversible capacity still higher than 1122 mAh g-1
(Fig 3(d)) On the contrary such high current density
results in the very lower reversible capacity of 92
mAh g-1 for bare TiO2 nanofibers (Fig S5(a) in the
ESM) and severe capacity fading (decrease to 128
mAh g-1 only after 50 cycles) (Fig S5(b) in the ESM)
It is obvious that FTHs demonstrate superior cyclic
capacity retention over the bare TiO2 nanofibers and
Fe3O4 nanoparticles counterpart thanks to the
synergistic effect Fig 3(e) shows the rate
performance of FTHs in comparison with that of
bare TiO2 nanofibers and Fe3O4 nanoparticles (Fig S6
in the ESM) At current densities of 02 04 06 2 4
and 6 A g-1 the reversible capacities of FTHs are 4814
3354 2978 1991 995 and 65 mAh g-1 respectively
which are about two times larger than that of bare
TiO2 electrode Most importantly when the current
density is reduced after the back and forth high rate
and 120 cycles measurement a discharge capacity of
3702 mAh g-1 can be recovered On the contrary the
Fe3O4 nanoparticles show bad rate performance
especially at high current density it shows scarcely
no capacity due to the large volume expansion and
severe particle aggregation which results in the
electrode pulverization capacity loss and poor
cycling stability
As a battery delivers high power large heat (the
so-called Joule effect) can be generated during the
chargedischarge process which would heat up the
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5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
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6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
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wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
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10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
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Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
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Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
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Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
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3 Nano Res
nanofibers
22 Characterization
Scanning electron microscopy (SEM) images were
collected with a Hitachi S-4800 instrument
Transmission electron microscope (TEM) images
were carried out with a Tecnai G2 using 200 kV X-ray
diffraction (XRD) patterns were carried out with a
Rigaku-Dmax 2500 diffractometer using Cu Kα
radiation X-ray photoelectron spectroscopy (XPS)
analysis was conducted with ESCALAB MK II X-ray
instrument
23 Electrochemical Evaluation
70 wt active materials (FTHs FTHfs TiO2
nanofibers Fe3O4 nanoparticles and TiO2-Fe3O4
mixture) 20 wt acetylene black and 10 wt
polyvinylidene fluoride (PVDF) were mixed in
N-methyl-2-pyrrolidone (NMP) and then uniformly
pasted on copper foil After finally dried in vacuum
at 80 for 12 h to remove the solvent the work
electrodes were pressed and cut into disks Thin
lithium foil was used as the counter electrode
Celgard 2400 membrane was used as separator and
lithium hexafluorophosphate LiPF6 (1 M) in ethylene
carbonatedimethyl carbonate (ECDMC 11 vol )
was employed as the electrolyte Galvanostatic
chargedischarge experiments were conducted in a
voltage range of 001-30 V with a Land Battery
Measurement System (Land China) The cyclic
voltammetry (CV 001-3 V 01 mV s-1) and
electrochemical impedance spectroscopy (EIS 01-700
kHz 5 mV) were conducted using a VMP3
Electrochemical Workstation (Bio-logic Inc)
3 Results and discussion
Scheme 1 illustrates the overall synthesis procedure
employed for the preparation of FTHs which is
briefly composed of the electrospinning and the
hydrothermal method Herein no surface
pretreatments are needed to introduce new surface
functional groups or additional covalent andor
noncovalent interconnectivity As a result perfectly
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures were obtained in high
yield The morphology of the prepared samples is
characterized by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) Fig 1(a)
and 1(b) show SEM images of bare TiO2 nanofibers
and FTHs The bare TiO2 non-woven nanofibers with
average diameter about 220 nm (Fig 1(a) inset) have
a relatively smooth surface The resulting materials
show hierarchical nanostructure and have diameters
of about 250 nm (Fig 1(b) inset) From TEM image in
Fig 1(c) it is obvious that the secondary Fe3O4
nanoparticles grow on the surface of TiO2 nanofibers
From the High-resolution transmission electron
microscopy (HRTEM) image of the heterojunction
region (Fig 1(d)) the observed two set of lattice
fringe spacings of 035 and 0254 nm are consistent
with the (101) plane of the anatase crystal structure of
TiO2 and the (311) plane of the cubic magnetite Fe3O4
respectively From the HRTEM image (Fig 1(e)) of
the nanoparticle it is also concluded that the
secondary Fe3O4 nanoparticles successfully grow on
the surface of the TiO2 nanofibers Furthermore
energy-dispersive X-ray spectroscopy (EDS)
characterization (Fig S1 in the Electronic
Supplementary Material (ESM)) also confirms that
FTHs include Fe Ti and O indicating the presence
of both Fe3O4 and TiO2 And EDS line scanning along
the cross section of FTHs (Fig 1(f)) further shows
that Fe is present only outside the TiO2 nanofibers
but not inside As a result Fe3O4
nanoparticle-decorated TiO2 nanofiber results in the
formation of the hierarchical Fe3O4TiO2 coreshell
nanofibers Moreover the thicknesses of the
secondary Fe3O4 nanoparticles are controllable by
simply changing the experimental parameters (Fig
S2 in the ESM)
The crystallographic structure of the prepared
samples is investigated by powder X-ray diffraction
(XRD) As shown in Fig 2(a) all the diffraction peaks
could be indexed to anatase TiO2 (JCPDS file No
21-1272) and cubic magnetite Fe3O4 (JCPDS file No
19-0629) X-ray photoelectron spectroscopy (XPS)
characterization is further carried out to analyze the
elemental composition As shown in Fig 2(b) the
XPS spectrum of FTHs shows the presence of the
Ti2p O1s and Fe2p peak For the high-resolution
Fe2p (Fig 2(b) inset) it is observed that two peaks of
Fe2p32 and Fe2p12 appear at 711 and 724 eV
respectively which demonstrates the secondary
nanostructures are Fe3O4 Then inductively coupled
plasma atomic emission spectrometry (ICP-AES) is
also carried out to test the actual iron contents in
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4 Nano Res
each sample The results show that the iron contents
are 140 and 182 wt in FTHs with few secondary
Fe3O4 nanoparticles (FTHfs) and FTHs respectively
The electrochemical performance of FTHs is
investigated as anode materials for LIBs Fig 3(a)
shows its cyclic voltammetry (CV) curves Two pairs
of redox current peaks can be clearly identified
during the cathodic and anodic scans In the first
cycle two current peaks appear at ~175 and ~21 V
respectively which can be regarded as the signature
of the lithium insertionextraction processes in the
anatase framework In addition the sharp reduction
peak at ~07 V can be ascribed to the conversion of
Fe3O4 to Fe and the formation of amorphous Li2O as
well as their irreversible reaction with the electrolyte
which may lead to the irreversible capacity At the
same time the wide oxidation peak at ~17 V could
be assigned to the reversible oxidation of Fe0 to Fe3+
during the anodic process [3839] For comparison
bare TiO2 nanofibers and Fe3O4 nanoparticles are also
tested The two pairs of well-shaped redox peaks for
TiO2 nanofibers (Fig S3(a) in the ESM) and Fe3O4
nanoparticles (Fig S3(b) in the ESM) are in good
agreement with those for FTHs Note that as
expected there is only a slight decrease in the peak
current during the subsequent cycles for TiO2
nanofibers indicating the highly reversible redox
reactions of TiO2 nanofibers In contrast the peak
current of the redox peaks of Fe3O4 nanoparticles
drops dramatically during the subsequent scans
indicating seriously irreversible reactions have taken
place in the Fe3O4 electrode thus leading to a severe
capacity fading upon charge-discharge cycling
Therefore we anticipate the reinforcement of Fe3O4
nanoparticles by stable TiO2 nanofibers can
effectively alleviate the severe capacity fading
Fig 3(b) shows the discharge-charge curves of
FTHs at 100 mA g-1 Consistent with the above CV
analysis two discharge plateaus at ~175 and 07 V
and two charge plateaus at ~17 and 21 V can be
clearly observed These voltage profiles are
characteristic of both Fe3O4-based and TiO2-based
materials The initial discharge and charge capacities
are found to be 7836 and 4945 mAh g-1 respectively
corresponding to a Coulombic efficiency of 631
Furthermore in the successive cycles the capacity of
the electrode scarcely decays and it can still deliver a
reversible capacity of 4545 mAh g-1 even after 200
cycles (Fig 3(b) and 3(c)) On the contrary the bare
TiO2 nanofibers electrode only exhibits a lower
reversible capacity of 202 mAh g-1 (Fig S4(a) in the
ESM) Although the Fe3O4 nanoparticles exhibits
higher initial discharge capacity of 10634 mAh g-1
(Fig S4(b) in the ESM) it suffers severe capacity
fading (decrease to 1577 mAh g-1 only after 70 cycles)
(Fig S4(c) in the ESM) which is lower than that of
FTHs indicating that the successful integration of
binary TiO2-Fe3O4 components can favourably inherit
the respective advantages from both TiO2 and Fe3O4
individual components Most importantly even at
high current densities the FTHs still exhibits good
cyclic capacity retention and it is able to deliver a
reversible capacity as high as 1878 mAh g-1 even
after 400 cycles at a current density of 1 A g-1 The
reversible capacity is maintained at 1343 mAh g-1
when the current density is increased to 2 A g-1 Even
at the very high current density of 3 A g-1 the
reversible capacity still higher than 1122 mAh g-1
(Fig 3(d)) On the contrary such high current density
results in the very lower reversible capacity of 92
mAh g-1 for bare TiO2 nanofibers (Fig S5(a) in the
ESM) and severe capacity fading (decrease to 128
mAh g-1 only after 50 cycles) (Fig S5(b) in the ESM)
It is obvious that FTHs demonstrate superior cyclic
capacity retention over the bare TiO2 nanofibers and
Fe3O4 nanoparticles counterpart thanks to the
synergistic effect Fig 3(e) shows the rate
performance of FTHs in comparison with that of
bare TiO2 nanofibers and Fe3O4 nanoparticles (Fig S6
in the ESM) At current densities of 02 04 06 2 4
and 6 A g-1 the reversible capacities of FTHs are 4814
3354 2978 1991 995 and 65 mAh g-1 respectively
which are about two times larger than that of bare
TiO2 electrode Most importantly when the current
density is reduced after the back and forth high rate
and 120 cycles measurement a discharge capacity of
3702 mAh g-1 can be recovered On the contrary the
Fe3O4 nanoparticles show bad rate performance
especially at high current density it shows scarcely
no capacity due to the large volume expansion and
severe particle aggregation which results in the
electrode pulverization capacity loss and poor
cycling stability
As a battery delivers high power large heat (the
so-called Joule effect) can be generated during the
chargedischarge process which would heat up the
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5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
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6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
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wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
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10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
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Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
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Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
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Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
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4 Nano Res
each sample The results show that the iron contents
are 140 and 182 wt in FTHs with few secondary
Fe3O4 nanoparticles (FTHfs) and FTHs respectively
The electrochemical performance of FTHs is
investigated as anode materials for LIBs Fig 3(a)
shows its cyclic voltammetry (CV) curves Two pairs
of redox current peaks can be clearly identified
during the cathodic and anodic scans In the first
cycle two current peaks appear at ~175 and ~21 V
respectively which can be regarded as the signature
of the lithium insertionextraction processes in the
anatase framework In addition the sharp reduction
peak at ~07 V can be ascribed to the conversion of
Fe3O4 to Fe and the formation of amorphous Li2O as
well as their irreversible reaction with the electrolyte
which may lead to the irreversible capacity At the
same time the wide oxidation peak at ~17 V could
be assigned to the reversible oxidation of Fe0 to Fe3+
during the anodic process [3839] For comparison
bare TiO2 nanofibers and Fe3O4 nanoparticles are also
tested The two pairs of well-shaped redox peaks for
TiO2 nanofibers (Fig S3(a) in the ESM) and Fe3O4
nanoparticles (Fig S3(b) in the ESM) are in good
agreement with those for FTHs Note that as
expected there is only a slight decrease in the peak
current during the subsequent cycles for TiO2
nanofibers indicating the highly reversible redox
reactions of TiO2 nanofibers In contrast the peak
current of the redox peaks of Fe3O4 nanoparticles
drops dramatically during the subsequent scans
indicating seriously irreversible reactions have taken
place in the Fe3O4 electrode thus leading to a severe
capacity fading upon charge-discharge cycling
Therefore we anticipate the reinforcement of Fe3O4
nanoparticles by stable TiO2 nanofibers can
effectively alleviate the severe capacity fading
Fig 3(b) shows the discharge-charge curves of
FTHs at 100 mA g-1 Consistent with the above CV
analysis two discharge plateaus at ~175 and 07 V
and two charge plateaus at ~17 and 21 V can be
clearly observed These voltage profiles are
characteristic of both Fe3O4-based and TiO2-based
materials The initial discharge and charge capacities
are found to be 7836 and 4945 mAh g-1 respectively
corresponding to a Coulombic efficiency of 631
Furthermore in the successive cycles the capacity of
the electrode scarcely decays and it can still deliver a
reversible capacity of 4545 mAh g-1 even after 200
cycles (Fig 3(b) and 3(c)) On the contrary the bare
TiO2 nanofibers electrode only exhibits a lower
reversible capacity of 202 mAh g-1 (Fig S4(a) in the
ESM) Although the Fe3O4 nanoparticles exhibits
higher initial discharge capacity of 10634 mAh g-1
(Fig S4(b) in the ESM) it suffers severe capacity
fading (decrease to 1577 mAh g-1 only after 70 cycles)
(Fig S4(c) in the ESM) which is lower than that of
FTHs indicating that the successful integration of
binary TiO2-Fe3O4 components can favourably inherit
the respective advantages from both TiO2 and Fe3O4
individual components Most importantly even at
high current densities the FTHs still exhibits good
cyclic capacity retention and it is able to deliver a
reversible capacity as high as 1878 mAh g-1 even
after 400 cycles at a current density of 1 A g-1 The
reversible capacity is maintained at 1343 mAh g-1
when the current density is increased to 2 A g-1 Even
at the very high current density of 3 A g-1 the
reversible capacity still higher than 1122 mAh g-1
(Fig 3(d)) On the contrary such high current density
results in the very lower reversible capacity of 92
mAh g-1 for bare TiO2 nanofibers (Fig S5(a) in the
ESM) and severe capacity fading (decrease to 128
mAh g-1 only after 50 cycles) (Fig S5(b) in the ESM)
It is obvious that FTHs demonstrate superior cyclic
capacity retention over the bare TiO2 nanofibers and
Fe3O4 nanoparticles counterpart thanks to the
synergistic effect Fig 3(e) shows the rate
performance of FTHs in comparison with that of
bare TiO2 nanofibers and Fe3O4 nanoparticles (Fig S6
in the ESM) At current densities of 02 04 06 2 4
and 6 A g-1 the reversible capacities of FTHs are 4814
3354 2978 1991 995 and 65 mAh g-1 respectively
which are about two times larger than that of bare
TiO2 electrode Most importantly when the current
density is reduced after the back and forth high rate
and 120 cycles measurement a discharge capacity of
3702 mAh g-1 can be recovered On the contrary the
Fe3O4 nanoparticles show bad rate performance
especially at high current density it shows scarcely
no capacity due to the large volume expansion and
severe particle aggregation which results in the
electrode pulverization capacity loss and poor
cycling stability
As a battery delivers high power large heat (the
so-called Joule effect) can be generated during the
chargedischarge process which would heat up the
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5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
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6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
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8 Nano Res
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wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
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10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
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Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
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Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
5 Nano Res
battery thus increasing the battery temperature
[40-42] Meanwhile in view of the changeability of
the ambient temperature it is thus of great
importance to investigate the temperature-dependent
performance of FTHs for practical applications
Measurements are carried out at 0 25 and 50
(Fig 3(e)) Interestingly at high temperature (50 )
FTHs can exhibit much enhanced rate performance
of 605 2691 and 70 mAh g-1 at the current densities
of 200 2000 and 6000 mA g-1 respectively Moreover
the voltage of the discharge plateaus and Coulombic
efficiency increase with the increase of temperature
(Fig S7 in the ESM) This might be attributed to
decrease of the battery resistance and increase of the
ion mobility of the electrolyte at elevated
temperature However at high temperature (50 )
the cycling stability decreases which could be
attributed to the degradation of the
electrodeelectrolyte interface and the decomposition
of the electrolyte promoted by high temperature
[40-42] On the contrary at low temperature (0 )
the cycling stability increases which could be
attributed to the formation of the stable solid
electrolyte interphase (SEI) film promoted by low
temperature In addition at low temperature (0 degC)
the battery can still deliver a high capacity of more
than 320 mAh g-1 at a current density of 200 mA g-1
Such promising results clearly demonstrate that
FTHs electrode is capable of working over a wide
temperature range
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures display good
electrochemical performance which could be
attributed to the successful integration of individual
components into the unique nanostructures The
controlled construction of 1D hierarchical structures
is convenient for keeping the effective contact areas
of active materials conductive additives and
electrolyte by preventing the self-aggregation of the
nanomaterials [7] providing more active sites for
lithium ion accesses to ensure a high utilization of
electrode materials and buffering drastic volume
change of the active materials occurring during
cycling Moreover the selection of proper metal
oxides including high capacity and high electronic
conductivity of Fe3O4 as hierarchical heterostructure
and durable electrochemically active TiO2 as stem
takes advantages of the merits of individual
components The enhancement more likely originates
from their synergistic effects instead of the simple
mix of two components which is elaborated as
follows On one hand the enhanced capacity of
hierarchical heterostructure compared with the bare
TiO2 nanofibers can be easily understood by the
addition of a higher capacity component Fe3O4
Additionally the Fe3O4 branches not only boost the
electronic conductivity of FTHs but also increase the
reversible electrochemical reaction of TiO2 with Li To
compare the conductivity of these samples the
electrochemical impedance spectroscopy (EIS)
measurements are carried out and the Nyquist plots
are depicted (Fig 4) All the Nyquist plots show a
semicircular loop at high-to-medium frequencies
and a sloping straight line is observed at low
frequencies The radius of the semicircular loop of
FTHs electrode is much smaller than that of the bare
TiO2 electrode indicating that the incorporation of
Fe3O4 could significantly enhance the conductivity of
FTHs which is vital for improving the
electrochemical performance In addition it is noted
that the electrochemical reaction mechanism of Fe3O4
with Li can be described by Fe3O4 + 8Li+ + 8e-
3Fe0 + 4Li2O As for TiO2 the electrochemical reaction
mechanism with Li can be written as TiO2 + xLi+ + xe-
4LixTiO2 Hence the presence of Fe nanoparticles
at the interface between Fe3O4 and TiO2 may improve
the reaction reversibility of TiO2 with Li and further
result in a higher reversible capacity [43] On the
other hand the synergistic effects endow the
as-prepared electrode material with structural
integrity In order to demonstrate the existence of
synergistic effects we compare the cycling
performance of TiO2Fe3O4 hierarchical
heterostructures with that of TiO2-Fe3O4 physical
mixture in the same proportion with FTHs (Fig 3(f))
Obviously the TiO2Fe3O4 nanofibers with few
secondary Fe3O4 nanoparticles (FTHfs) could inherit
the good cycling performance of TiO2 and also show
the increased capacity compared with bare TiO2
nanofibers With the increase of secondary Fe3O4
nanoparticles FTHs show the more increased
performance On the contrary although the
TiO2-Fe3O4 physical mixture electrode exhibits higher
initial discharge capacity it suffers severe capacity
fading These results clearly demonstrate Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
| wwweditorialmanagercomnaredefaultasp
6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
[1] Tarascon J M Armand M Issues and challenges facing
rechargeable lithium batteries Nature 2001 414 359-367
[2] Poizot P Laruelle S Grugeon S Dupont L Tarascon J
M Nano-sized transition-metal oxides as
negative-electrode materials for lithium-ion batteries
Nature 2000 407 496-499
[3] Chen J Xu L Li W Gou X α-Fe2O3 nanotubes in gas
sensor and lithium-ion battery applications Adv Mater
2005 17 582-586
[4] Yu Y Chen C H Shi Y A tin-based amorphous oxide
composite with a porous spherical multideck-cage
morphology as a highly reversible anode material for
lithium-ion batteries Adv Mater 2007 19 993-997
[5] Chen J Cheng F Y Combination of lightweight elements
and nanostructured materials for batteries Acc Chem Res
2009 42713-723
[6] Wang B Chen J S Wu H B Wang Z Y Lou X W
Quasiemulsion-templated formation of α-Fe2O3 hollow
spheres with enhanced lithium storage properties J Am
Chem Soc 2011 133 17146-17148
[7] Mai L Xu L Han C Xu X Luo Y Zhao S Zhao Y
Electrospun ultralong hierarchical vanadium oxide
nanowires with high performance for lithium ion batteries
Nano Lett 2010 10 4750-4755
[8] Luo W Hu X L Sun Y M Huang Y H
Electrospinning of carbon-coated MoO2 nanofibers with
enhanced lithium-storage properties Phys Chem Chem
Phys 2011 13 16735-16740
[9] Shi Y F Guo B K Corr S A Shi Q S Hu Y-S
Heier K R Chen L Q Seshadri R Stucky G D
Ordered mesoporous metallic MoO2 materials with highly
reversible lithium storage capacity Nano Lett 2009 9
4215-4220
[10] Huang X-L Wang R-Z Xu D Wang Z-L Wang
H-G Xu J-J Wu Z Liu Q-C Zhang Y Zhang X-B
Homogeneous CoO on graphene for binder-free and
ultralong-life lithium ion batteries Adv Funct Mater
2013 23 4345-4353
[11] Lai X Y Halpert J E Wang D Recent advances in
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
7 Nano Res
micro-nano-structured hollow spheres for energy
applications From simple to complex systems Energy
Environ Sci 2012 5 5604-5618
[12] Wang J Y Yang N L Tang H J Dong Z H Jin Q
Yang M Kisailus D Zhao H J Tang Z Y Wang D
Accurate control of multishelled Co3O4 hollow
microspheres as high-performance anode materials in
lithium-ion batteries Angew Chem Int Ed 2013 52
6417-6420
[13] Xu S M Hessel C M Ren H Yu R B Jin Q
Yang M Zhao H J Wang D α-Fe2O3 multi-shelled
hollow microspheres for lithium ion battery anodes with
superior capacity and charge retention Energy Environ Sci
2014 27 632-637
[14] Hu Y S Kienle L Guo Y G Maier J High lithium
electroactivity of nanometer-sized rutile TiO2 Adv Mater
2006 18 1421-1426
[15] Liu J H Chen J S Wei X F Lou X W Liu X W
Sandwich-like stacked ultrathin titanate nanosheets for
ultrafast lithium storage Adv Mater 2011 23 998-1002
[16] Ren H Yu R B Wang J Y Jin Q Yang M Mao D
Kisailus D Zhao H J Wang D Multi-shelled TiO2
hollow microspheres as anodes with superior reversible
capacity for lithium ion batteries Nano Lett 2014 DOI
101021nl503378a
[17] Wu H B Chen J S Lou X W Hng H H
Asymmetric anatase TiO2 nanocrystals with exposed
high-index facets and their excellent lithium storage
properties Nanoscale 2011 3 4082-4084
[18] Armstrong A R Armstrong G Canales J Garciacutea R
Bruce P G Lithium-ion intercalation into TiO2-B
nanowires Adv Mater 2005 17 862-865
[19] Wagemaker M Borghols W J H Mulder F M Large
impact of particle size on insertion reactions A case for
anatase LixTiO2 J Am Chem Soc 2007 129 4323-4327
[20] Chen X Mao S S Titanium dioxide nanomaterialsthinsp
synthesis properties modifications and applications
Chem Rev 2007 107 2891-2959
[21] Rahman M M Wang J Z Hassan M F Wexler D
Liu H K Amorphous carbon coated high grain boundary
density dual phase Li4Ti5O12-TiO2 A nanocomposite anode
material for Li-ion batteries Adv Energy Mater 2011 1
212-220
[22] Luo W Hu X L Sun Y M Huang Y H Surface
modification of electrospun TiO2 nanofibers via
layer-by-layer self-assembly for high-performance
lithium-ion batteries J Mater Chem 2012 22 4910-4915
[23] Zhang X Chen H X Xie Y P Guo J X Ultralong
life lithium-ion battery anode with superior high-rate
capability and excellent cyclic stability from mesoporous
Fe2O3TiO2 corendashshell nanorods J Mater Chem A 2014
2 3912-3918
[24] Luo Y S Luo J S Jiang J Zhou W W Yang H P
Qi X Y Zhang H Fan H J Yu D Y W Li C
M Yu T Seed-assisted synthesis of highly ordered
TiO2α-Fe2O3 coreshell arrays on carbon textiles for
lithium-ion battery applications Energy Environ Sci 2012
5 6559-6566
[25] Wang H G Ma D L Huang X L Yuan S Zhang X
B General and controllable synthesis strategy of metal
oxideTiO2 hierarchical heterostructures with improved
lithium-ion battery performance Sci Rep 2012 2 701
[26] Yang Z X Du G D Meng Q Guo Z P Yu X
B Chen Z X Guo T L Zeng R Dispersion of SnO2
nanocrystals on TiO2(B) nanowires as anode material for
lithium ion battery applications RSC Adv 2011 1
1834-1840
[27] Parka H Song T Han H Devadoss A Yuh J Choi
C Paik U SnO2 encapsulated TiO2 hollow nanofibers as
anode material for lithium ion batteries Electrochem
Commun 2012 22 81-84
[28] Jeun J-H Park K-Y Kim D-H Kim W-S Kim
H-C Lee B-S Kim H Yu W-R Kang K Hong
S-H SnO2TiO2 double-shell nanotubes for a lithium ion
battery anode with excellent high rate cyclability
Nanoscale 2013 5 8480-8483
[29] Nam S H Shim H S Kim Y S Dar M A Kim J G
Kim W B Ag or Au nanoparticle-embedded
one-dimensional composite TiO2 nanofibers prepared via
electrospinning for use in lithium-ion batteries ACS Appl
Mater Interface 2010 2 2046-2052
[30] He B L Dong B Li H L Preparation and
electrochemical properties of Ag-modified TiO2 nanotube
anode material for lithium-ion battery Electrochem
Commun 2007 9 425-430
[31] Taberna P L Mitra S Poizot P Simon P Tarascon J
M High rate capabilities Fe3O4-based Cu
nano-architectured electrodes for lithium-ion battery
applications Nat Mater 2006 5 567-573
[32] Zhang W M Wu X L Hu J S Guo Y G Wan L J
Carbon coated Fe3O4 nanospindles as a superior anode
material for lithium-ion batteries Adv Funct Mater 2008
18 3941-3946
[33] Zhu T Chen J S Lou X W Glucose-assisted one-pot
synthesis of FeOOH nanorods and their transformation to
Fe3O4carbon nanorods for application in lithium ion
batteries J Phys Chem C 2011 115 9814-9820
[34] Wu Y Wei Y Wang J P Jiang K L Fan S S
Conformal Fe3O4 sheath on aligned carbon nanotube
scaffolds as high-performance anodes for lithium ion
batteries Nano Lett 2013 13 818-823
[35] Lv P P Zhao H L Zeng Z P Wang J Zhang T H
Li X W Facile preparation and electrochemical properties
of carbon coated Fe3O4 as anode material for lithium-ion
batteries J Power Sources 2014 259 92-97
[36] Ito S Nakaoko K Kawamura M Ui K Fujimoto K
Koura N Lithium battery having a large capacity using
Fe3O4 as a cathode material J Power Sources 2005 146
319-322
[37] Mitra S Poizot P Finke A Tarascon J M Growth and
electrochemical characterization versus lithium of Fe3O4
electrodes made by electrodeposition Adv Funct Mater
2006 16 2281-2287
[38] Liu H Wang G Wang J Wexler D Magnetitecarbon
core-shell nanorods as anode materials for lithium-ion
batteries Electrochem Commun 2008 10 1879-1882
[39] Zhou G Wang D W Li F Zhang L Li N Wu Z S
Wen L Lu G Q Cheng H M Graphene-wrapped Fe3O4
| wwweditorialmanagercomnaredefaultasp
8 Nano Res
anode material with improved reversible capacity and
cyclic stability for lithium ion batteries Chem Mater 2010
22 5306-5313
[40] Choi S H Son J W Yoon Y S Kim J Particle size
effects on temperature-dependent performance of LiCoO2
in lithium batteries J Power Sources 2006 158
1419-1424
[41] Masarapu C Zeng H F Hung K H Wei B Q Effect
of temperature on the capacitance of carbon nanotube
supercapacitors ACS Nano 2009 3 2199-2206
[42] Yan J Sumboja A Khoo E Lee P S V2O5 loaded on
SnO2 nanowires for high-rate Li ion batteries Adv Mater
2011 23 746-750
[43] Zhou W W Cheng C W Liu J P Tay Y Y Jiang J
Jia X T Zhang J X Gong H Hng H H Yu T Fan
H J Epitaxial growth of branched α-Fe2O3SnO2
nano-heterostructures with improved lithium-ion battery
performance Adv Funct Mater 2011 21 2439-2445
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
| wwweditorialmanagercomnaredefaultasp
10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
| wwweditorialmanagercomnaredefaultasp
6 Nano Res
heterostructures could result in the synergistic effects
which play very important role in keeping the
structural integrity thus enhancing the cycling
performance To confirm the structural integrity of
FTHs electrode we observed the morphology of
FTHs after charge-discharge cycles using SEM and
TEM After cycling FTHs still maintained their
hierarchical heterostructures without any mechanical
degradation coinciding with the original
morphology (Fig S8(a) and inset in the ESM) Herein
the reason can be the following the 1D hierarchical
heterostructures may relieve the strain caused by
severe volume change of Fe3O4 during the numerous
charge-discharge cycles and thus suppress the
degradation of the electrode material as
schematically demonstrated in Fig 5(a) In contrast
TiO2-Fe3O4 physical mixture could not buffer the
large volume expansion (Fig S8(b) in the ESM) and
part of Fe3O4 nanoparticles were disintegrated into
nanoparticles (Fig S9 in the ESM) during Li+
insertionextraction resulted from the large volume
expansion of Fe3O4 as schematically demonstrated in
Fig 5(b) These observations corroborate that
hierarchical heterostructures are very effective for
accommodating the large volume expansion of Fe3O4
nanoparticles and improving cycle life
4 Conclusions
In summary we fabricated Fe3O4
nanoparticle-decorated TiO2 nanofiber hierarchical
heterostructures by a facile effective and scalable
method Interestingly the electrochemical results
clearly demonstrated that the advantageous
integration of TiO2 and Fe3O4 into 1D hierarchical
nanostructure can foster strengths and circumvent
weaknesses of individual components and thus
simultaneously exerts higher reversible capacity
excellent cyclability and good rate performance
which would open up new idea in the combination
of the merits of individual components to develop
high performance electrode materials for LIBs The
proposed synthesis strategy can be easily extended to
prepare other composite metal oxide materials
which can be used in broad fields including
electrochemical capacitors and sensors
Acknowledgements
This work is financially supported by the
fundamental research funds for the central
universities the National Natural Science
Foundation of China (Grant No 51372007 and
21301014)
Electronic Supplementary Material Supplementary
material (EDS spectrum of FTHs SEM images of
FTHfs CVs charge-discharge curves cycling
performance and rate performance of TiO2
nanofibers and Fe3O4 nanoparticles) is available in
the online version of this article at
httpdxdoiorg101007s12274---
(automatically inserted by the publisher) References
[1] Tarascon J M Armand M Issues and challenges facing
rechargeable lithium batteries Nature 2001 414 359-367
[2] Poizot P Laruelle S Grugeon S Dupont L Tarascon J
M Nano-sized transition-metal oxides as
negative-electrode materials for lithium-ion batteries
Nature 2000 407 496-499
[3] Chen J Xu L Li W Gou X α-Fe2O3 nanotubes in gas
sensor and lithium-ion battery applications Adv Mater
2005 17 582-586
[4] Yu Y Chen C H Shi Y A tin-based amorphous oxide
composite with a porous spherical multideck-cage
morphology as a highly reversible anode material for
lithium-ion batteries Adv Mater 2007 19 993-997
[5] Chen J Cheng F Y Combination of lightweight elements
and nanostructured materials for batteries Acc Chem Res
2009 42713-723
[6] Wang B Chen J S Wu H B Wang Z Y Lou X W
Quasiemulsion-templated formation of α-Fe2O3 hollow
spheres with enhanced lithium storage properties J Am
Chem Soc 2011 133 17146-17148
[7] Mai L Xu L Han C Xu X Luo Y Zhao S Zhao Y
Electrospun ultralong hierarchical vanadium oxide
nanowires with high performance for lithium ion batteries
Nano Lett 2010 10 4750-4755
[8] Luo W Hu X L Sun Y M Huang Y H
Electrospinning of carbon-coated MoO2 nanofibers with
enhanced lithium-storage properties Phys Chem Chem
Phys 2011 13 16735-16740
[9] Shi Y F Guo B K Corr S A Shi Q S Hu Y-S
Heier K R Chen L Q Seshadri R Stucky G D
Ordered mesoporous metallic MoO2 materials with highly
reversible lithium storage capacity Nano Lett 2009 9
4215-4220
[10] Huang X-L Wang R-Z Xu D Wang Z-L Wang
H-G Xu J-J Wu Z Liu Q-C Zhang Y Zhang X-B
Homogeneous CoO on graphene for binder-free and
ultralong-life lithium ion batteries Adv Funct Mater
2013 23 4345-4353
[11] Lai X Y Halpert J E Wang D Recent advances in
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
7 Nano Res
micro-nano-structured hollow spheres for energy
applications From simple to complex systems Energy
Environ Sci 2012 5 5604-5618
[12] Wang J Y Yang N L Tang H J Dong Z H Jin Q
Yang M Kisailus D Zhao H J Tang Z Y Wang D
Accurate control of multishelled Co3O4 hollow
microspheres as high-performance anode materials in
lithium-ion batteries Angew Chem Int Ed 2013 52
6417-6420
[13] Xu S M Hessel C M Ren H Yu R B Jin Q
Yang M Zhao H J Wang D α-Fe2O3 multi-shelled
hollow microspheres for lithium ion battery anodes with
superior capacity and charge retention Energy Environ Sci
2014 27 632-637
[14] Hu Y S Kienle L Guo Y G Maier J High lithium
electroactivity of nanometer-sized rutile TiO2 Adv Mater
2006 18 1421-1426
[15] Liu J H Chen J S Wei X F Lou X W Liu X W
Sandwich-like stacked ultrathin titanate nanosheets for
ultrafast lithium storage Adv Mater 2011 23 998-1002
[16] Ren H Yu R B Wang J Y Jin Q Yang M Mao D
Kisailus D Zhao H J Wang D Multi-shelled TiO2
hollow microspheres as anodes with superior reversible
capacity for lithium ion batteries Nano Lett 2014 DOI
101021nl503378a
[17] Wu H B Chen J S Lou X W Hng H H
Asymmetric anatase TiO2 nanocrystals with exposed
high-index facets and their excellent lithium storage
properties Nanoscale 2011 3 4082-4084
[18] Armstrong A R Armstrong G Canales J Garciacutea R
Bruce P G Lithium-ion intercalation into TiO2-B
nanowires Adv Mater 2005 17 862-865
[19] Wagemaker M Borghols W J H Mulder F M Large
impact of particle size on insertion reactions A case for
anatase LixTiO2 J Am Chem Soc 2007 129 4323-4327
[20] Chen X Mao S S Titanium dioxide nanomaterialsthinsp
synthesis properties modifications and applications
Chem Rev 2007 107 2891-2959
[21] Rahman M M Wang J Z Hassan M F Wexler D
Liu H K Amorphous carbon coated high grain boundary
density dual phase Li4Ti5O12-TiO2 A nanocomposite anode
material for Li-ion batteries Adv Energy Mater 2011 1
212-220
[22] Luo W Hu X L Sun Y M Huang Y H Surface
modification of electrospun TiO2 nanofibers via
layer-by-layer self-assembly for high-performance
lithium-ion batteries J Mater Chem 2012 22 4910-4915
[23] Zhang X Chen H X Xie Y P Guo J X Ultralong
life lithium-ion battery anode with superior high-rate
capability and excellent cyclic stability from mesoporous
Fe2O3TiO2 corendashshell nanorods J Mater Chem A 2014
2 3912-3918
[24] Luo Y S Luo J S Jiang J Zhou W W Yang H P
Qi X Y Zhang H Fan H J Yu D Y W Li C
M Yu T Seed-assisted synthesis of highly ordered
TiO2α-Fe2O3 coreshell arrays on carbon textiles for
lithium-ion battery applications Energy Environ Sci 2012
5 6559-6566
[25] Wang H G Ma D L Huang X L Yuan S Zhang X
B General and controllable synthesis strategy of metal
oxideTiO2 hierarchical heterostructures with improved
lithium-ion battery performance Sci Rep 2012 2 701
[26] Yang Z X Du G D Meng Q Guo Z P Yu X
B Chen Z X Guo T L Zeng R Dispersion of SnO2
nanocrystals on TiO2(B) nanowires as anode material for
lithium ion battery applications RSC Adv 2011 1
1834-1840
[27] Parka H Song T Han H Devadoss A Yuh J Choi
C Paik U SnO2 encapsulated TiO2 hollow nanofibers as
anode material for lithium ion batteries Electrochem
Commun 2012 22 81-84
[28] Jeun J-H Park K-Y Kim D-H Kim W-S Kim
H-C Lee B-S Kim H Yu W-R Kang K Hong
S-H SnO2TiO2 double-shell nanotubes for a lithium ion
battery anode with excellent high rate cyclability
Nanoscale 2013 5 8480-8483
[29] Nam S H Shim H S Kim Y S Dar M A Kim J G
Kim W B Ag or Au nanoparticle-embedded
one-dimensional composite TiO2 nanofibers prepared via
electrospinning for use in lithium-ion batteries ACS Appl
Mater Interface 2010 2 2046-2052
[30] He B L Dong B Li H L Preparation and
electrochemical properties of Ag-modified TiO2 nanotube
anode material for lithium-ion battery Electrochem
Commun 2007 9 425-430
[31] Taberna P L Mitra S Poizot P Simon P Tarascon J
M High rate capabilities Fe3O4-based Cu
nano-architectured electrodes for lithium-ion battery
applications Nat Mater 2006 5 567-573
[32] Zhang W M Wu X L Hu J S Guo Y G Wan L J
Carbon coated Fe3O4 nanospindles as a superior anode
material for lithium-ion batteries Adv Funct Mater 2008
18 3941-3946
[33] Zhu T Chen J S Lou X W Glucose-assisted one-pot
synthesis of FeOOH nanorods and their transformation to
Fe3O4carbon nanorods for application in lithium ion
batteries J Phys Chem C 2011 115 9814-9820
[34] Wu Y Wei Y Wang J P Jiang K L Fan S S
Conformal Fe3O4 sheath on aligned carbon nanotube
scaffolds as high-performance anodes for lithium ion
batteries Nano Lett 2013 13 818-823
[35] Lv P P Zhao H L Zeng Z P Wang J Zhang T H
Li X W Facile preparation and electrochemical properties
of carbon coated Fe3O4 as anode material for lithium-ion
batteries J Power Sources 2014 259 92-97
[36] Ito S Nakaoko K Kawamura M Ui K Fujimoto K
Koura N Lithium battery having a large capacity using
Fe3O4 as a cathode material J Power Sources 2005 146
319-322
[37] Mitra S Poizot P Finke A Tarascon J M Growth and
electrochemical characterization versus lithium of Fe3O4
electrodes made by electrodeposition Adv Funct Mater
2006 16 2281-2287
[38] Liu H Wang G Wang J Wexler D Magnetitecarbon
core-shell nanorods as anode materials for lithium-ion
batteries Electrochem Commun 2008 10 1879-1882
[39] Zhou G Wang D W Li F Zhang L Li N Wu Z S
Wen L Lu G Q Cheng H M Graphene-wrapped Fe3O4
| wwweditorialmanagercomnaredefaultasp
8 Nano Res
anode material with improved reversible capacity and
cyclic stability for lithium ion batteries Chem Mater 2010
22 5306-5313
[40] Choi S H Son J W Yoon Y S Kim J Particle size
effects on temperature-dependent performance of LiCoO2
in lithium batteries J Power Sources 2006 158
1419-1424
[41] Masarapu C Zeng H F Hung K H Wei B Q Effect
of temperature on the capacitance of carbon nanotube
supercapacitors ACS Nano 2009 3 2199-2206
[42] Yan J Sumboja A Khoo E Lee P S V2O5 loaded on
SnO2 nanowires for high-rate Li ion batteries Adv Mater
2011 23 746-750
[43] Zhou W W Cheng C W Liu J P Tay Y Y Jiang J
Jia X T Zhang J X Gong H Hng H H Yu T Fan
H J Epitaxial growth of branched α-Fe2O3SnO2
nano-heterostructures with improved lithium-ion battery
performance Adv Funct Mater 2011 21 2439-2445
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
| wwweditorialmanagercomnaredefaultasp
10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
7 Nano Res
micro-nano-structured hollow spheres for energy
applications From simple to complex systems Energy
Environ Sci 2012 5 5604-5618
[12] Wang J Y Yang N L Tang H J Dong Z H Jin Q
Yang M Kisailus D Zhao H J Tang Z Y Wang D
Accurate control of multishelled Co3O4 hollow
microspheres as high-performance anode materials in
lithium-ion batteries Angew Chem Int Ed 2013 52
6417-6420
[13] Xu S M Hessel C M Ren H Yu R B Jin Q
Yang M Zhao H J Wang D α-Fe2O3 multi-shelled
hollow microspheres for lithium ion battery anodes with
superior capacity and charge retention Energy Environ Sci
2014 27 632-637
[14] Hu Y S Kienle L Guo Y G Maier J High lithium
electroactivity of nanometer-sized rutile TiO2 Adv Mater
2006 18 1421-1426
[15] Liu J H Chen J S Wei X F Lou X W Liu X W
Sandwich-like stacked ultrathin titanate nanosheets for
ultrafast lithium storage Adv Mater 2011 23 998-1002
[16] Ren H Yu R B Wang J Y Jin Q Yang M Mao D
Kisailus D Zhao H J Wang D Multi-shelled TiO2
hollow microspheres as anodes with superior reversible
capacity for lithium ion batteries Nano Lett 2014 DOI
101021nl503378a
[17] Wu H B Chen J S Lou X W Hng H H
Asymmetric anatase TiO2 nanocrystals with exposed
high-index facets and their excellent lithium storage
properties Nanoscale 2011 3 4082-4084
[18] Armstrong A R Armstrong G Canales J Garciacutea R
Bruce P G Lithium-ion intercalation into TiO2-B
nanowires Adv Mater 2005 17 862-865
[19] Wagemaker M Borghols W J H Mulder F M Large
impact of particle size on insertion reactions A case for
anatase LixTiO2 J Am Chem Soc 2007 129 4323-4327
[20] Chen X Mao S S Titanium dioxide nanomaterialsthinsp
synthesis properties modifications and applications
Chem Rev 2007 107 2891-2959
[21] Rahman M M Wang J Z Hassan M F Wexler D
Liu H K Amorphous carbon coated high grain boundary
density dual phase Li4Ti5O12-TiO2 A nanocomposite anode
material for Li-ion batteries Adv Energy Mater 2011 1
212-220
[22] Luo W Hu X L Sun Y M Huang Y H Surface
modification of electrospun TiO2 nanofibers via
layer-by-layer self-assembly for high-performance
lithium-ion batteries J Mater Chem 2012 22 4910-4915
[23] Zhang X Chen H X Xie Y P Guo J X Ultralong
life lithium-ion battery anode with superior high-rate
capability and excellent cyclic stability from mesoporous
Fe2O3TiO2 corendashshell nanorods J Mater Chem A 2014
2 3912-3918
[24] Luo Y S Luo J S Jiang J Zhou W W Yang H P
Qi X Y Zhang H Fan H J Yu D Y W Li C
M Yu T Seed-assisted synthesis of highly ordered
TiO2α-Fe2O3 coreshell arrays on carbon textiles for
lithium-ion battery applications Energy Environ Sci 2012
5 6559-6566
[25] Wang H G Ma D L Huang X L Yuan S Zhang X
B General and controllable synthesis strategy of metal
oxideTiO2 hierarchical heterostructures with improved
lithium-ion battery performance Sci Rep 2012 2 701
[26] Yang Z X Du G D Meng Q Guo Z P Yu X
B Chen Z X Guo T L Zeng R Dispersion of SnO2
nanocrystals on TiO2(B) nanowires as anode material for
lithium ion battery applications RSC Adv 2011 1
1834-1840
[27] Parka H Song T Han H Devadoss A Yuh J Choi
C Paik U SnO2 encapsulated TiO2 hollow nanofibers as
anode material for lithium ion batteries Electrochem
Commun 2012 22 81-84
[28] Jeun J-H Park K-Y Kim D-H Kim W-S Kim
H-C Lee B-S Kim H Yu W-R Kang K Hong
S-H SnO2TiO2 double-shell nanotubes for a lithium ion
battery anode with excellent high rate cyclability
Nanoscale 2013 5 8480-8483
[29] Nam S H Shim H S Kim Y S Dar M A Kim J G
Kim W B Ag or Au nanoparticle-embedded
one-dimensional composite TiO2 nanofibers prepared via
electrospinning for use in lithium-ion batteries ACS Appl
Mater Interface 2010 2 2046-2052
[30] He B L Dong B Li H L Preparation and
electrochemical properties of Ag-modified TiO2 nanotube
anode material for lithium-ion battery Electrochem
Commun 2007 9 425-430
[31] Taberna P L Mitra S Poizot P Simon P Tarascon J
M High rate capabilities Fe3O4-based Cu
nano-architectured electrodes for lithium-ion battery
applications Nat Mater 2006 5 567-573
[32] Zhang W M Wu X L Hu J S Guo Y G Wan L J
Carbon coated Fe3O4 nanospindles as a superior anode
material for lithium-ion batteries Adv Funct Mater 2008
18 3941-3946
[33] Zhu T Chen J S Lou X W Glucose-assisted one-pot
synthesis of FeOOH nanorods and their transformation to
Fe3O4carbon nanorods for application in lithium ion
batteries J Phys Chem C 2011 115 9814-9820
[34] Wu Y Wei Y Wang J P Jiang K L Fan S S
Conformal Fe3O4 sheath on aligned carbon nanotube
scaffolds as high-performance anodes for lithium ion
batteries Nano Lett 2013 13 818-823
[35] Lv P P Zhao H L Zeng Z P Wang J Zhang T H
Li X W Facile preparation and electrochemical properties
of carbon coated Fe3O4 as anode material for lithium-ion
batteries J Power Sources 2014 259 92-97
[36] Ito S Nakaoko K Kawamura M Ui K Fujimoto K
Koura N Lithium battery having a large capacity using
Fe3O4 as a cathode material J Power Sources 2005 146
319-322
[37] Mitra S Poizot P Finke A Tarascon J M Growth and
electrochemical characterization versus lithium of Fe3O4
electrodes made by electrodeposition Adv Funct Mater
2006 16 2281-2287
[38] Liu H Wang G Wang J Wexler D Magnetitecarbon
core-shell nanorods as anode materials for lithium-ion
batteries Electrochem Commun 2008 10 1879-1882
[39] Zhou G Wang D W Li F Zhang L Li N Wu Z S
Wen L Lu G Q Cheng H M Graphene-wrapped Fe3O4
| wwweditorialmanagercomnaredefaultasp
8 Nano Res
anode material with improved reversible capacity and
cyclic stability for lithium ion batteries Chem Mater 2010
22 5306-5313
[40] Choi S H Son J W Yoon Y S Kim J Particle size
effects on temperature-dependent performance of LiCoO2
in lithium batteries J Power Sources 2006 158
1419-1424
[41] Masarapu C Zeng H F Hung K H Wei B Q Effect
of temperature on the capacitance of carbon nanotube
supercapacitors ACS Nano 2009 3 2199-2206
[42] Yan J Sumboja A Khoo E Lee P S V2O5 loaded on
SnO2 nanowires for high-rate Li ion batteries Adv Mater
2011 23 746-750
[43] Zhou W W Cheng C W Liu J P Tay Y Y Jiang J
Jia X T Zhang J X Gong H Hng H H Yu T Fan
H J Epitaxial growth of branched α-Fe2O3SnO2
nano-heterostructures with improved lithium-ion battery
performance Adv Funct Mater 2011 21 2439-2445
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
| wwweditorialmanagercomnaredefaultasp
10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
| wwweditorialmanagercomnaredefaultasp
8 Nano Res
anode material with improved reversible capacity and
cyclic stability for lithium ion batteries Chem Mater 2010
22 5306-5313
[40] Choi S H Son J W Yoon Y S Kim J Particle size
effects on temperature-dependent performance of LiCoO2
in lithium batteries J Power Sources 2006 158
1419-1424
[41] Masarapu C Zeng H F Hung K H Wei B Q Effect
of temperature on the capacitance of carbon nanotube
supercapacitors ACS Nano 2009 3 2199-2206
[42] Yan J Sumboja A Khoo E Lee P S V2O5 loaded on
SnO2 nanowires for high-rate Li ion batteries Adv Mater
2011 23 746-750
[43] Zhou W W Cheng C W Liu J P Tay Y Y Jiang J
Jia X T Zhang J X Gong H Hng H H Yu T Fan
H J Epitaxial growth of branched α-Fe2O3SnO2
nano-heterostructures with improved lithium-ion battery
performance Adv Funct Mater 2011 21 2439-2445
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
| wwweditorialmanagercomnaredefaultasp
10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
9 Nano Res
Figure 1 Morphology characterization Low- and high-
resolution (inset) SEM images of (a) bare TiO2 nanofibers and (b)
FTHs (c) Typical TEM image of the single FTH (d) HRTEM
image of the heterojunction region (e) HRTEM image of the
surface nanoparticle (f) TEM image and line-scanning (indicated
by a line) elemental mapping along the cross section
Figure 2 Phase analysis (a) XRD patterns of bare TiO2
nanofibers and FTHs (b) Survey XPS spectrum and
high-resolution Fe2p spectra of FTHs (inset)
Figure 3 Electrochemical properties (a) CVs of FTHs at a scan
rate of 01 mV s-1 in the range of 3-001 V (b) Discharge and
charge curves of FTHs at 100 mA g-1 (c) Cycling performance of
bare TiO2 nanofibers and FTHs at 100 mA g-1 (d) Rate
performance of bare TiO2 nanofibers and FTHs obtained at 25
(e) Rate performance of FTHs obtained at 0 25 and 50 at
different current densities (f) Cycling performance of bare TiO2
nanofibers FTHfs FTHs and TiO2-Fe3O4 physical mixture at 100
mA g-1
Figure 4 Electrochemical impedance spectra Nyquist plots
before cycling for bare TiO2 nanofibers Fe3O4 nanoparticles and
FTHs by applying an AC voltage of 5 mV amplitude at 01 to 700
kHz
| wwweditorialmanagercomnaredefaultasp
10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
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Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
| wwweditorialmanagercomnaredefaultasp
10 Nano Res
Figure 5 Scheme of the proposed mechanism Schematics of the
electrochemical process in various configuration electrodes (a)
FTHs and (b) TiO2-Fe3O4 physical mixture
Scheme 1 Schematic diagram showing the strategy for
preparation of the FTHs
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Electronic Supplementary Material
Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures with improved lithium-ion
battery performance over a wide temperature range
Heng-guo Wang2 Guang-sheng Wang1 Shuang Yuan3 De-long Ma3 Yang Li1 and Yu Zhang1()
Supporting information to DOI 101007s12274--- (automatically inserted by the publisher)
Experimental Section
Materials
Poly(vinyl pyrrolidone) (PVP Mw = 1 300 000 Aldrich) acetic acid (AR Aladdin Reagent) ethanol (AR
Aladdin Reagent) titanium butyloxide (CP Aladdin Reagent) FeCl3middot6H2O (AR Aladdin Reagent) polyethylene
glycol (PEG AR Aladdin Reagent) sodium acetate (NaAc AR Aladdin Reagent) ethylene glycol (EG AR
Aladdin Reagent) N-methylpyrrolidone (NMP Aladdin Reagent AR) acetone (AR Shanghai Chemicals
China) acetylene black (Hong-xin Chemical Works) polyvinylidenefluoride (PVDF DuPont Company 999)
Separator (polypropylene film Celgard 2400) Electrolyte for lithium ion batteries (1 M LiPF6 in ethylene
carbonate (EC)dimethyl carbonate (DMC) with the weight ratio of 11 Zhangjiagang Guotai-Huarong New
Chemical Materials Co Ltd All the reagents used in the experiment were of analytical grade purity and were
used as received De-ionized water with the specific resistance of 182 MΩcm was obtained by reversed
osmosis followed by ion-exchange and filtration
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S1 Energy-dispersive X-ray spectroscopy (EDS) spectrum of FTHs on TEM girds
Figure S2 (a) Low- and (b) high- resolution SEM images of the few secondary Fe3O4 nanoparticle-decorated TiO2 nanofiber
hierarchical heterostructures For comparison the TiO2Fe3O4 nanofibers with few secondary Fe3O4 nanoparticles (FTHfs) were also
prepared under the same condition instead of the addition of FeCl3middot6H2O (005 g)
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S3 CVs of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at a scan rate of 01 mV s-1 in the range of 3-001 V
Figure S4 Discharge and charge curves of bare TiO2 nanofibers (a) and Fe3O4 nanoparticles (b) at 100 mA g-1 (c) Cycling performance
of Fe3O4 nanoparticles at 100 mA g-1
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Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S5 Cycling performance of FTHs (a) bare TiO2 nanofibers (b) and Fe3O4 nanoparticles (c) at various current densities of 1 2
and 3 A g-1
Figure S6 Rate performance of Fe3O4 nanoparticles at various current densities
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
wwwtheNanoResearchcom∣wwwSpringercomjournal12274 | Nano Research
Nano Res
Figure S7 Discharge and charge curves of FTHs at a current density of 200 mA g-1 obtained at 0 (a) 25 (b) and 50 (c) (d) The
discharge curves of FTHs electrode tested at a current density of 200 mA g-1 at different temperatures
Figure S8 (a) SEM and (inset) TEM images of FTHs electrode after 20 cycles at 100 mA g-1 (b) SEM images of TiO2-Fe3O4 physical
mixture electrode after 20 cycles at 100 mA g-1
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Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn
| wwweditorialmanagercomnaredefaultasp
Nano Res
Figure S9 (a) Low- and (b) high- resolution SEM images of Fe3O4 nanoparticles before cycling (c) Low- and (d) high- resolution SEM
images of Fe3O4 nanoparticles after 60 cycles at 100 mA g-1
Address correspondence to Yu Zhang email jadebuaaeducn