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Electrochimica Acta
jou rn al hom epa ge: www.elsev ier .com/ locate /e lec tac ta
ynthesis of Li2CoTi3O8 fibers and their application to lithium-ion batteries
i Wanga,b, Qizhen Xiaoa,b,∗, Zhaohui Lib, Gangtie Leib, Lijuan Wub, Ping Zhanga,∗, Jun Maob
College of Civil Engineering & Mechanics, Xiangtan University, Hunan 411105, ChinaKey Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Hunan 411105, China
r t i c l e i n f o
rticle history:eceived 7 March 2012eceived in revised form 22 May 2012ccepted 23 May 2012vailable online 30 May 2012
a b s t r a c t
Li2CoTi3O8 fibers have been synthesized by an electrospinning method and investigated as an anodematerial for rechargeable lithium-ion batteries. The structure and electrochemical properties of theLi2CoTi3O8 fibers were systematically investigated. Characterization of data collected with high-resolution transmission electron microscopy and scanning electron microscopy reveal that the Li2CoTi3O8
fibers have an average diameter of 300 nm, and the individual fiber is composed of nanoparticles with
an average diameter of 48 nm. The nanoparticles not only shorten the distance for Li-ions and electronsto transport but also possess good electrodes electronic contact and high surface area. The results ofelectrochemical measurements show that the as-prepared Li2CoTi3O8 electrode deliver a specific capac-ity of 388 mAh g−1 for the first cycle with an irreversible capacity of 156 mAh g−1 and finally remains237 mAh g−1 after 30 cycles at 50 mA g−1. Its electrochemical performance at subsequent cycles exhibitshigh cycling capacity and rate capability.
. Introduction
Lithium-ion batteries (LIBs) are currently the dominant powerource for portable electronic devices and electrical/hybrid vehi-les [1]. For an anode material in LIBs, graphite is usually employeds a standard electrode because it can be reversibly charged andischarged under intercalation potentials with reasonable spe-ific capacity (theoretical capacity is 372 mAh g−1). However, toeet the increasing demand for high capacity and high power,any efforts have been made recently to develop new electrodeaterials or design novel structures of electrode materials for
ext-generation LIBs [2–4]. Recent reports stated that Li can beeversibly intercalated into the compound Li2MTi3O8 (M = Zn,Cu)hich has attracted increasing attention for LIBs because of theirigh specific lithium storage capacity and cycling stability [5,6].he Li2CoTi3O8 [7,8] and Li2ZnTi3O8 [9] both exhibit a cubic struc-ure with similar lattice constants. Previous reported results showhat the Li2CoTi3O8 exhibits higher reactivity than Li2MgTi3O8 andi2ZnTi3O8 towards lithium insertion in the bulk form [8]. Hongt al. [10] reported the synthesis of Li2CoTi3O8 nanowires using
itanate nanowires as a precursor. It was found that the structuref the synthesized Li2CoTi3O8 retained significant stability dur-ng lithium-ions intercalation and deintercalation, and therefore
∗ Corresponding authors at: College of Chemistry, Xiangtan University, Xiangtan,unan 411105, China. Tel.: +86 731 58292206; fax: +86 731 58292477.
the anodes made of Li2CoTi3O8 nanowires had a large reversiblecapacity and a high rate performance.
Nanometer-sized active materials in the electrode of lithiumrechargeable batteries, compared to conventional micrometer-sized materials, have attracted much attention due to the fasttransport of lithium ion species as facilitated by a shortened diffu-sion length. The electrospinning approach provides a flexible wayto prepare large-scale nanomaterials to fulfill the requirements forelectrode materials. There have been lots of researches on the useof electrospinning method to synthesize materials in the lithiumion battery field, such as Li2ZnTi3O8 fibers [9], electrospun carbon-silicon composite nanofiber [11], C/Fe3O4 composite nanofibers[12], activated carbon nanofibers [13], electrospun vanadium pen-toxide nanofibers [14], and electrospun porous SnO2 nanotubes[15]. It has been reported that electrospun carbon-silicon com-posite nanofibers exhibited a large reversible specific capacity of1240 mAh g−1 and excellent capacity retention [11]. Wang et al.reported C/Fe3O4 composite nanofibers prepared by combiningelectrospinning and carbonization processes, exhibited good elec-trochemical performance with a high reversible specific capacity of1007 mAh g−1 at the 80th cycle and excellent rate capability [12].The electrospun porous SnO2 nanotubes delivered a high specificcapacity of 807 mAh g−1 after 50 cycles and still retained a highfraction of its theoretical capacity even after cycled at high rates[15].
Inspired by these studies, we succeeded in synthesizingLi2CoTi3O8 with fibers structure through an electrospinning pro-cess. The morphology, crystal structure and electrochemicalproperties of Li2CoTi3O8 fibers were systematically investigated
n detail. The results of electrochemical measurements indicatehat the anode material made of spinel Li2CoTi3O8 fibers exhibitn excellent cycling stability and high rate capability.
. Experimental
The Li2CoTi3O8 fibers were prepared by combining the sol–gelhemistry and electrospinning technique. The solution for elec-rospinning was prepared from tetrabutyl titanate (TBT), cobaltcetate (C4H6O4Co·4H2O), lithium acetate (LiOAc), polymethyl-ethacrylate (PMMA, MW = 600,000), N,N-dimethylformamide
DMF) and acetic acid. All chemicals were obtained from Aldrich.n a typical process, TBT (1.50 g), C4H6O4Co·H2O (0.366 g),H3COOLi·2H2O (0.315 g), PMMA (2.50 g) and acetic acid (2.0 mL)ere added to a solvent of DMF (12.0 mL). The mixture was then
tirred for 24 h to obtain a precursor solution, which was subse-uently loaded into a one-off injector with a spinneret made oftainless steel. The distance between the spinneret and the collectoras 20 cm, and the applied voltage was 28 kV. The solution was fed
y a pump at a rate of 0.25 mL h−1. Finally, the obtained electrospunbers membrane was dried in a vacuum oven at 100 ◦C overnight,nd then calcined at 750 ◦C for 10 h at a heating rate of 1 ◦C min−1
t air to obtain Li2CoTi3O8 fibers. For comparison, Li2CoTi3O8 bulkarticles were also synthesized by solid-state reaction adoptingiOAc, C4H6O4Co·4H2O and rutile TiO2 as the raw materials.
The morphologies and structures were observed by scanninglectron microscopy (SEM, JEOL JSM-6360) and high-resolutionransmission electron microscopy (HRTEM, JEOL 3010). The crystaltructure of Li2CoTi3O8 fibers was determined by X-ray diffractionXRD, Rigaku D/max 2550) pattern (Cu K� radiation) at a scan ratef 10◦ min−1. The thermal behavior of the gel precursor was char-cterized by thermogravimetry (TG) in the SDTQ 600 instrumentanged from 20 to 800 ◦C at a heating rate of 10 ◦C min−1 in air.
The electrodes for electrochemical evaluation were preparedy mixing 70 wt.% active material, 20 wt.% carbon black (Super), and 10 wt.% polyvinylidene fluoride (PVdF) dissolved in N-ethyl-pyrrolidinone (NMP) to form a slurry which was coated
nto a copper foil and dried at 120 ◦C for 12 h in vacuum. Thelectrodes were then assembled into CR2016 coin cells in an Ar-lled glove box using Celgard polypropylene separator, 1 M LiPF6
n ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, v/v) elec-rolyte, and lithium foil as the counter and reference electrodes. Theischarge–charge experiments were carried out galvanostaticallyt different current densities within the voltage range of 3.0–0.05 Vs. Li/Li+, using an Arbin charge–discharge unit. Electrochemicalmpedance spectroscopic analysis (EIS) was also investigated by theotentiostat/Galvannostat M273 in conjunction with the M5210ock-in amplifier instrument with an AC voltage of 5 mV amplituden the frequency range from 100 kHz to 0.01 Hz.
. Results and discussion
Fig. 1 shows the TG/DTG curves of the electrospuno(CH3COO)2/LiOAc/TBT/PMMA fibers at a heating rate of0 ◦C min−1 under air atmosphere. It is found that there arehree weight losses during heating the fibers from room temper-ture to 800 ◦C, corresponding to the three peaks in the curve ofTG. The weight loss in the range of room temperature to 100 ◦Cay be related to the evaporation of absorbed water from the pre-
ursor fibers. Subsequently, a small weight loss (200–320 ◦C) mayriginate from the decomposition of lithium acetate, cobalt acetate
nd tetrabutyl titanate. In the temperature range of 320–500 ◦C,he significant weight loss suggests the thermal decomposition ofhe PMMA. There is no obvious weight loss from 500 to 800 ◦C,ndicating that the decomposition reaction is completed before
Fig. 1. TG/DTG curves of the electrospun Co(CH3COO)2/LiOAc/TBT/PMMA fibers ata heating rate of 10 ◦C min−1 under air atmosphere.
500 ◦C. We choose 750 ◦C to calcine the lithium titanate fibersprecursor and synthesize the product, which is important formaintaining the fiber morphology and obtaining high crystallineLi2CoTi3O8.
Fig. 2a shows SEM image of the electrospunCo(CH3COO)2/LiOAc/TBT/PMMA fibers. All fibers exhibit a long andstraight morphology with relatively uniform diameters rangingfrom 200 to 500 nm. Fig. 2b shows a SEM image of the Li2CoTi3O8fibers formed by electrospinning approach. These Li2CoTi3O8 fiberscan be mass produced with diameters in the range of 100–430 nm.As shown in Fig. 2c, each individual Li2CoTi3O8 fiber is composedof small particles. The selected-area electron diffraction (SAED)exhibits a cubic pattern. Clear and continuous lattice-fringe imagescan be observed in Fig. 2c (inset), and the distance betweenneighboring fringes was measured to be 0.213 nm, close to that ofthe (4 0 0) lattice spacing (0.209 nm) in the cubic Li2CoTi3O8 (JCPDSNo: 49-0449) lattice, which indicates that the structure of theformed fibers is cubic Li2CoTi3O8. The SEM image of the Li2CoTi3O8bulk particles prepared by solid-state reaction is shown in Fig. 2d.It is clearly observed that the average particle size of the powderis 400 nm with a distribution of 250–600 nm. As shown in the areamarked with solid lines of Fig. 2e, the sloped spacing is 0.1480 nm,which corresponds to the (0 0 2) lattice spacing (0.1479 nm) in therutile TiO2 (JCPDS No: 78-1509) lattice. It can be obviously seenthat the small amount of TiO2 impurities are uniformly dispersedin the Li2CoTi3O8 matrix.
Fig. 3 shows XRD pattern of the Li2CoTi3O8 fibers, which isobtained by calcining the precursor at 750 ◦C for 10 h at a heat-ing rate of 1 ◦C min−1 under air atmosphere. All diffraction peaksare marked on the XRD pattern. The main diffraction peaks at2� = 18.3◦, 35.5◦, 57.1◦, can be attributed to (1 1 1), (3 1 1), (5 1 1)reflections of the cubic structure of spinel Li2CoTi3O8 with P4332space group (JCPDS No: 89-1309). Some minor peaks detected at2� = 27.4◦, 41.2◦ and 54.3◦ can be assigned to rutile TiO2 impurity.The crystalline size (D) was calculated using the Scherrer equation
cos(�) = k�/D, where ˇ is the half-peak width of the XRD diffrac-tion peak, � is the position of the peak, � is wavelength of CuK�radiation and k is a constant (0.89) [16]. It is found that the aver-age crystalline size (D) of the Li2CoTi3O8 fibers is calculated to be48 nm.
Fig. 4a and b shows CV curves of the Li2CoTi3O8 fibers and theLi2CoTi3O8 bulk particles electrodes for the first five cycles. Com-pared to the Li2CoTi3O8 bulk particles electrodes, the oxidationpeak at 1.72 V for the Li2CoTi3O8 fibers are more stable and nearlyoverlap each other for the first five cycles, indicating that inter-
calation/deintercalation of lithium ions into/out of the Li2CoTi3O8fibers electrode are highly reversible. Fig. 4c shows the 2nd cycleCV curves of the Li2CoTi3O8 fibers and the Li2CoTi3O8 bulk parti-cles electrodes at a scan rate of 0.1 mV s−1. The peak intensity for
L. Wang et al. / Electrochimica Acta 77 (2012) 77– 82 79
F ) SEMi s of tho
trtearsibfst
ig. 2. (a) SEM image of the electrospun Co(CH3COO)2/LiOAc/TBT/PMMA fibers, (bmage of Li2CoTi3O8 fibers (inset, SAED pattern and HRTEM image), (d) SEM imagef the TiO2 impurity.
he bulk particles is clearly weaker than that for the fibers, whicheveals that the anode made of the fibers has a higher activity inhe electrochemical reaction. The CV curves of the Li2CoTi3O8 fiberlectrodes in the voltage range of 3.0–0.05 V at various scan ratesre shown in Fig. 4d. It can be seen obviously that one couple ofedox peaks (above 1.5 V) exist at the various scan rates, corre-ponding to the insertion and extraction process of lithium ionsnto and from the Li2CoTi3O8 anode. Meanwhile, a reduction peak
elow 0.5 V is observed, which might be related to the different sitesor lithium-ion intercalation and deintercalation in such a spineltructure [10]. As shown in Fig. 4b, the cathodic peak currents ofhe cyclic voltammograms are in proportion to the square root of
images of the Li2CoTi3O8 fibers synthesized by electrospinning method, (c) TEMe Li2CoTi3O8 bulk particles prepared by solid-state reaction, and (e) HRTEM image
the scan rate, v1/2. Based on the CV data at different scan rates andthe following equation [17]:
Ip = 2.69 × 105An3/2C0D1/2�1/2 (1)
where n is the number of electrons per molecule during the inter-calation, A is the surface area of the anode (since the real surfacearea of the electrode is difficult to measure, here the geometricsurface area of the electrode was used), C0 is the concentration
of lithium ions (0.0226 mol cm−3, calculated from the volume ofLi2CoTi3O8 (587.8 A3 [8])), D is the diffusion coefficient of lithiumions and v is the scan rate; the diffusion coefficient of lithium ionsin the electrode can be calculated. Since the real surface area of
80 L. Wang et al. / Electrochimica
tafiFo[oisps
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−1
Fbc
Fig. 3. XRD pattern of the Li2CoTi3O8 fibers.
he electrode is difficult to measure, here the geometric surfacerea of the electrode was used. The lithium ions diffusion coef-cient in the Li2CoTi3O8 is calculated to be 1.41 × 10−8 cm2 s−1.or comparison, lithium ions diffusion coefficient for Li4Ti5O12 isnly 10−12–10−13 cm2 s−1 [18,19]. Li2CoTi3O8 can be described asLi0.5Co0.45]tet[(Li0.5Co0.05)Ti1.5]octO4 [10] and be built on two setsf octahedrons of TiO6 and Li(Co)O6, with Li and Co atoms locatedn tetrahedral sites forming tunnels. Therefore, a three dimen-ional (3D) network is formed in such a structure that provides the
athway for lithium-ions diffusion. Thus Li2CoTi3O8 could bringignificant improvement in lithium-ion diffusion.
Fig. 5a shows the profiles of voltage versus capacity of thei2CoTi3O8 fibers and Li2CoTi3O8 bulk particles electrodes at
ig. 4. Cyclic voltammograms of Li2CoTi3O8 bulk particles (a) and the fibers (b) electrodeulk particles electrodes at 2nd cycle at a scan rate of 0.1 mV s−1. (d) Cyclic voltammograurrents of the cyclic voltammograms are in proportion to square root of the scan rate, v1
Acta 77 (2012) 77– 82
100 mA g−1 at the 30th cycle between 3.0 and 0.05 V. It is foundthat the fibers electrode gives a much higher specific capacityand 100 mV higher discharge plateau than those of the bulk par-ticles. This indicates a larger polarization has happened betweenthe bulk particles during charge–discharge cycles. Chan et al. [20]demonstrated that the fibers sample could increase its electrodeselectronic contact, thus bring significant improvement in the elec-trochemical performance. It can be found that the discharge specificcapacity of the Li2CoTi3O8 fibers is 237 mAh g−1 at 100 mA g−1 at30th cycle. It was reported that a Li4Ti5O12 electrode exhibited dis-charge specific capacity of about 225 mAh g−1 when the dischargevoltage is close to 0.0 V at current density of 0.078 Am cm−2, whichis lower than those of the Li2CoTi3O8 [21].
The profiles of voltage versus capacity of the Li2CoTi3O8 fibersat different current densities are shown in Fig. 5b. The com-pound shows an initial discharge specific capacity of 388 mAh g−1
with an irreversible capacity loss of 156 mAh g−1 during thefirst charge and discharge cycle (50 mA g−1). Two plateaus areobserved at 1.41 V and 0.38 V at the initial discharge process.The plateau of 1.41 V is not present in the second or subsequentcycles. This result might be caused by irreversible reactions atthe surface, such as the formation of a solid electrolyte interface(SEI) composed of organic lithium alkylcarbonates [22]. Anotherreason for the initial irreversible capacity loss is that the materialcould be lithiated chemically. The electrochemical reaction ofLi2CoTi3O8 with lithium-ion can be described as the follow-ing: [LiCo0.9]tet[(LiCo0.1)Ti3]octO8 + 3e− + 3Li+ → [Li4]oct[Co0.9]tet
[(LiCo0.1)Ti3]octO8. The fully lithiated Li2CoTi3O8 has a high theo-
retical capacity of 233 mAh g . It can be explained as follows: (1)lithium-ions at tetrahedral sites move to octahedral sites and theinserted lithium-ions also occupy octahedral sites in the dischargeprocess; (2) lithium-ions could also occupy other tetrahedral
s at a scan rate of 0.1 mV s−1 (c) Cyclic voltammograms of the Li2CoTi3O8 fibers andms of the Li2CoTi3O8 fibers electrode at various scan rates (inset, the cathodic peak/2).
L. Wang et al. / Electrochimica Acta 77 (2012) 77– 82 81
Fig. 5. (a) The profiles of voltage versus specific capacity for the Li2CoTi3O8 fibers,and bulk particles electrodes at 100 mAg−1 at 30 cycles between 3.0 and 0.05 V. (b)Td
swlowa(
ai[wrh
acc5c5orrtilnn1
were collected on as assembled cells at the voltage of 2.1 V, respec-tively. As shown in Fig. 8, the EIS spectra consist of a semicircleand a line. The diameter of the semicircle (at medium–low fre-quency region) is a measure of the charge transfer resistance, which
he profiles of voltage versus specific capacity for the Li2CoTi3O8 fibers electrode atifferent current densities.
ites since octahedral sites are fully occupied already [21,23],hich is in agreement with the CV results. However, some of the
ithium-ions occupying the tetrahedral sites cannot be extractedut reversibly. Contributing to the initial irreversible capacity loss,hich is also the reason that the initial discharge specific capacity
t 50 mA g−1 (388 mAh g−1) is higher than the theoretical capacity233 mAh g−1).
As shown in Fig. 5b, the plateaus at 1.63 V for the charge profilesnd 0.56 V for the discharge profiles are evident in the second cycle,n agreement with previous observations for Li2CoTi3O8 anodes10]. On the other hand, the discharge voltage of battery decreasesith increasing current density due to kinetic effects of the mate-
ial such as diffusion of both Li-ions and electrons, in other wordigh current density causes higher overpotential [24].
Fig. 6 shows rate performances of (a) the Li2CoTi3O8 fibersnd (b) the Li2CoTi3O8 bulk particles electrodes at differenturrent densities between 3.0 and 0.05 V. The galvanostaticharge–discharge current density was increased gradually from0 to 2000 mA g−1. For the Li2CoTi3O8 fibers, a specific dis-harge capacity of 237 mAh g−1 is obtained at a current density of0 mA g−1 after 30 cycles; a reversible discharge specific capacityf 222, 199, 176, and 142 mAh g−1 is observed at the discharge cur-ent densities of 100, 200, 1000 and 2000 mA g−1 after 30 cycles,espectively. However, the reversible discharge specific capacity ofhe Li2CoTi3O8 bulk particles at the corresponding current densitys 141, 126, 116, 114, and 103 mAh g−1, respectively, significantlyower than that of the Li CoTi O fibers prepared by electrospin-
2 3 8ing (Fig. 6). Recently, Hong et al. [10] reported that Li2CoTi3O8anowires exhibited a stable specific capacity of 230 mAh g−1 and00 mAh g−1 at 100 mA g−1 and 1600 mA g−1, respectively. It is
Fig. 6. Rate performances of the Li2CoTi3O8 fibers, and bulk particles electrodes atdifferent current densities between 3.0 and 0.05 V.
obvious that the rate capability of Li2CoTi3O8 prepared by the elec-trospinning method is better than that obtained by Hong et al. It wasreported that Li2MgTi3O8 nanowires exhibited the specific capaci-ties of 180 mAh g−1 and 70 mAh g−1 at 100 mA g−1 and 800 mA g−1,respectively [25]. Hong et al. [5] reported that the stable specificcapacities of Li2ZnTi3O8 nanorods at 100 mA g−1 and 200 mA g−1
are 220 mAh g−1 and 200 mAh g−1, respectively. The results showthat as-prepared Li2CoTi3O8 fibers have high rate capability. Suchgood rate capability results from the fibers structure which is com-posed of nanoparticles. They shorten the distance for Li-ions andelectron transport. In addition, they have good electrodes electroniccontact and high surface area, which is a high electrode–electrolytecontract area. Thus both electron and Li+ transport could finally beimproved.
To evaluate the cycling stability of the Li2CoTi3O8 fibers elec-trode, it was further charge–discharged at a current density of2000 mA g−1 for another 300 cycles after the 150 cycles electro-chemical tests performed at 50, 100, 200, 1000, and 2000 mA g−1.As shown in Fig. 7, the Li2CoTi3O8 fibers electrode shows a sta-ble cycle life. The specific discharge capacity of the sample is136 mAh g−1 after the 150 cycles electrochemical tests performedat 50, 100, 200, 1000, and 2000 mA g−1, and even after another 300charge–discharge cycles at 2000 mA g−1, its specific capacity stillremains at 141 mAh g−1.
In order to gain further insight into the electrochemical per-formances, electrochemical impedance spectra were measured forboth the Li2CoTi3O8 fibers and bulk particles electrodes. The data
Fig. 7. Cycle performance of Li2CoTi3O8 fibers electrode at a current density of2000 mA g−1.
82 L. Wang et al. / Electrochimica
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[[[[[23] L. Aldon, P. Kubaik, M. Womes, J.C. Jumas, J.O. Fourcade, J.L. Tirado, J.I. Corredor,
ig. 8. The impedance spectra of the Li2CoTi3O8 fibers and bulk particles electrodeinset, equivalent circuit of Li2CoTi3O8 electrode).
s related to the electrochemical reaction between the electrodend the electrolyte. The sloping line is related to lithium-ions dif-usion in the bulk of the active material. The EIS spectra fitted usingn equivalent circuit is shown in Fig. 8 (inset), where Re repre-ents electrolyte bulk resistance between working electrode andithium reference electrode, CPE1 is used as a constant phase ele-
ent, Rct represents charge transfer resistance, and Zw representsarburg impedance. It shows the impedance of Rct is 536 � for
he Li2CoTi3O8 bulk particles electrode, whereas it reduces drasti-ally to 206 � for the Li2CoTi3O8 fibers electrode, indicating that thei2CoTi3O8 fibers electrode possesses lower charge transfer resis-ance than the bulk particles electrode. The result is consistent withhe good rate capability.
. Conclusions
Li2CoTi3O8 fibers have been successfully synthesized via elec-rospinning method followed by thermal treating. All Li2CoTi3O8bers exhibit a long and straight morphology with relativelyniform diameters. Especially, the individual Li2CoTi3O8 fiber isomposed of small particles of 48 nm in diameter. Electrochemi-al measurements indicate that Li2CoTi3O8 fibers electrode deliver
specific capacity of 388 mAh g−1 for the first cycle with an irre-ersible capacity of 156 mAh g−1 and the special capacity remains37 mAh g−1 after 30 cycles at 50 mA g−1. Its electrochemical per-
ormance at subsequent cycles exhibits high cycling capacity andate capability. These values are by far quite higher than thosexhibited by bulk particles sample prepared by solid state reaction,esulting from the good electronic contact and high surface area for
[[
Acta 77 (2012) 77– 82
the fibers. Moreover, the material displays excellent cycling stabil-ity even at a high current rate of 2000 mA g−1. These results showthat the Li2CoTi3O8 fibers are a highly promising anode materialfor Li-ion battery application.
Acknowledgements
This work was financially sponsored by the National Post-Doctoral Fund of China (No. 20090461013), innovation experi-mental program of Xiangtan University, the project of Science andTechnology of Hunan Province (No. 2010RS4012).
References
[1] M. Armand, J.M. Tarascon, Nature 451 (2008) 652.[2] Y. Yu, L. Gu, C. Wang, A. Dhanabalan, P.A. Aken, J. Maier, Angewandte Chemie
International Edition 48 (2009) 6485.[3] J.-M. Tarascon, M. Armand, Nature 414 (2001) 359.[4] P.G. Bruce, B. Scrosati, J.-M. Tarascon, Angewandte Chemie International Edition
mental Science 4 (2011) 1886.11] L. Wang, C.X. Ding, L.C. Zhang, H.W. Xu, D.W. Zhang, T. Cheng, C.H. Chen, Journal
of Power Sources 195 (2010) 5052.12] L. Wang, Y. Yu, P.C. Chen, D.W. Zhang, C.H. Chen, Journal of Power Sources 183
(2008) 717.13] L.W. Ji, X.W. Zhang, Electrochemistry Communications 11 (2009) 684.14] Y.L. Cheah, N. Gupta, S.S. Pramana, V. Aravindan, G. Wee, M. Srinivasan, Journal
of Power Sources 196 (2011) 6465.15] L.M. Li, X.M. Yin, S. Liu, Y.G. Wang, L.B. Chen, T.H. Wang, Electrochemistry
Communications 12 (2010) 1383.16] C. Venkateswara Rao, B. Rambabu, Solid State Ionics 181 (2010) 839.17] J.R. Dahn, J.W. Jiang, L.M. Moshurchak, M.D. Fleischauer, C. Buhrmester,
L.J. Krause, Journal of the Electrochemical Society 152 (2005)A1283.
18] T. Yuan, X. Yu, R. Cai, Y.K. Zhou, Z.P. Shao, Journal of Power Sources 195 (2010)4997.
19] D. Fattakhova, P.J. Krtil, Electrochemical Society 149 (2002) A1224.20] C.K. Chan, X.F. Zhang, Y. Cui, Nano Letters 8 (2008) 307.21] J. Shu, Journal of Solid State Electrochemistry 13 (2009) 1535.22] J. Shu, Electrochemical and Solid State Letters 11 (2008) A238.
C.P. Vicente, Chemistry of Materials 16 (2004) 5721.24] R. Xu, J. Li, Z. Tang, Z. Zhang, Journal of Nanomaterials 2011 (2011) 1.25] Z.S. Hong, T.B. Lan, Y.Z. Zheng, L.L. Jiang, K.M. Wei, Functional Materials Letters
