Facile synthesis of carbon nanotubes supported NiO nanocomposite and its high performance as lithium-ion battery anode Syed Mustansar Abbas a,b,n , Syed Tajammul Hussain a , Saqib Ali b,nn , Khurram Shahzad Munawar b , Nisar Ahmad c , Nisar Ali d a Nanoscience and Catalysis Division, National Centre for Physics, Islamabad, Pakistan b Department of Chemistry, Quaid-e-Azam University, Islamabad, Pakistan c Department of Chemistry, Hazara University, Mansehra, Pakistan d Department of Physics, University of Punjab, Lahore, Pakistan article info Article history: Received 12 January 2013 Accepted 29 May 2013 Available online 6 June 2013 Keywords: Nanocomposite Carbon nanotubes Nanosize FTIR X-ray techniques abstract NiO nanocrystals anchored on carbon nanotubes (CNTs) were fabricated via a polyvinylpyrrolidone assisted co-precipitation route. At a current density of 100 mA g -1 , the composite anode delivers an initial reversible capacity of 962 mA h g -1 and retains the capacity to 601 mA h g -1 after 50 cycles. In contrast, the reversible capacity of the pure NiO particles faded to 380 mA h g -1 immediately and then gradually decreased to 278 mA h g -1 after 50 cycles. The significantly improved electrochemical performance of the NiO/CNT nanocomposite is attributed to the formation of conductive networks by CNTs, and large surface areas of NiO nanoparticles grown on CNTs which stabilizes these nanoparticles against agglomeration and reduces the diffusion length for lithium-ions. The present results indicate that NiO/CNT nanocomposite has potential applications in lithium-ion battery anodes. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The increasing demand for high energy-density power sources has promoted an intense research to develop new anode materials for lithium-ion batteries (LIBs), from lithium intercalation/extrac- tion materials such as graphite to Li-alloying metals like Sn and Si [1,2]. Due to their high theoretical energy-densities, 3d transition metal oxide (TMO) anode materials (MO x ,M¼ Fe,Co,Ni,Mn,Cu etc.) based on a conversion mechanism have also been investigated in the last few years [3–7]. Among these TMOs, NiO shows more advantages in terms of theoretical capacity of 718 mA h g -1 , which is higher than CuO and Cu 2 O, and it is less expensive than CoO [8]. In recent years, NiO anode with different morphologies like, flower-like [9], porous [10,11], core–shell [12], nanocone-array [13] and hollow-NiO microspheres [14] showed attractive electro- chemical performance. However, its large volume expansion/con- traction associated with the Li-insertion and extraction process lead to electrode pulverization and loss of interparticle contact and consequently, results in a large irreversible capacity loss and poor cycling stability. To alleviate the above problem and further enhance the structural stability, hybridizing NiO with carbon nanotubes (CNTs) is an effective method to accommodate the strain of volume change during lithium insertion/extraction processes. CNTs are promising support materials for anchoring well-dispersed nano- particles because of their unique one-dimensional tubular struc- ture, favorable electrical conductivity, high specific surface area and excellent structural flexibility [15–17]. Consequently, we have reasons to expect that for NiO/CNT nanocomposite, nanoscale Ni has the possibility to facilitate the decomposition of Li 2 O and the solid electrolyte interface (SEI) film during the charging process while net-structured CNTs can prevent the pulverization during the charge/discharge cycle and improve the conductivity. In this work, a new hybrid nanocomposite consisting of NiO and CNTs is prepared as an anode material for LIBs. Compared to NiO nanopowder, high performance is achieved for NiO/CNT nanocomposite as LIB anode. 2. Experimental The CNTs used in this work were prepared by our patented technology (Patent number:US2009208403) using chemical vapor deposition (CVD) and were functionalized by UV/O 3 treatment. For functionalization, CNTs were initially exposed to UV for 1h followed by 10 min ozone exhaust at room temperature and pressure [18]. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.141 n Corresponding author at: Department of Chemistry, Quaid-e-Azam University, Islamabad, Pakistan. Tel.: +92 3218539839; fax: +92 512077395. nn Corresponding author. Tel.: +5190642130. E-mail addresses: [email protected] (S. Mustansar Abbas), drsa54@yahoo. com (S. Ali). Materials Letters 107 (2013) 158–161
Transcript
Materials Letters 107 (2013) 158–161
Contents lists available at SciVerse ScienceDirect
Materials Letters
0167-57http://d
n CorrIslamab
nn CorE-m
com (S.
journal homepage: www.elsevier.com/locate/matlet
Facile synthesis of carbon nanotubes supported NiO nanocompositeand its high performance as lithium-ion battery anode
Syed Mustansar Abbas a,b,n, Syed Tajammul Hussain a, Saqib Ali b,nn,Khurram Shahzad Munawar b, Nisar Ahmad c, Nisar Ali d
a Nanoscience and Catalysis Division, National Centre for Physics, Islamabad, Pakistanb Department of Chemistry, Quaid-e-Azam University, Islamabad, Pakistanc Department of Chemistry, Hazara University, Mansehra, Pakistand Department of Physics, University of Punjab, Lahore, Pakistan
a r t i c l e i n f o
Article history:Received 12 January 2013Accepted 29 May 2013Available online 6 June 2013
7X/$ - see front matter & 2013 Elsevier B.V. Ax.doi.org/10.1016/j.matlet.2013.05.141
esponding author at: Department of Chemistad, Pakistan. Tel.: +92 3218539839; fax: +92 5responding author. Tel.: +5190642130.ail addresses: [email protected] (S. MustAli).
a b s t r a c t
NiO nanocrystals anchored on carbon nanotubes (CNTs) were fabricated via a polyvinylpyrrolidoneassisted co-precipitation route. At a current density of 100 mA g−1, the composite anode delivers aninitial reversible capacity of 962 mA h g−1 and retains the capacity to 601 mA h g−1 after 50 cycles.In contrast, the reversible capacity of the pure NiO particles faded to 380 mA h g−1 immediately and thengradually decreased to 278 mA h g−1 after 50 cycles. The significantly improved electrochemicalperformance of the NiO/CNT nanocomposite is attributed to the formation of conductive networks byCNTs, and large surface areas of NiO nanoparticles grown on CNTs which stabilizes these nanoparticlesagainst agglomeration and reduces the diffusion length for lithium-ions. The present results indicate thatNiO/CNT nanocomposite has potential applications in lithium-ion battery anodes.
& 2013 Elsevier B.V. All rights reserved.
1. Introduction
The increasing demand for high energy-density power sourceshas promoted an intense research to develop new anode materialsfor lithium-ion batteries (LIBs), from lithium intercalation/extrac-tion materials such as graphite to Li-alloying metals like Sn and Si[1,2]. Due to their high theoretical energy-densities, 3d transitionmetal oxide (TMO) anode materials (MOx, M¼Fe,Co,Ni,Mn,Cu etc.)based on a conversion mechanism have also been investigated inthe last few years [3–7]. Among these TMOs, NiO shows moreadvantages in terms of theoretical capacity of 718 mA h g−1, whichis higher than CuO and Cu2O, and it is less expensive than CoO [8].In recent years, NiO anode with different morphologies like,flower-like [9], porous [10,11], core–shell [12], nanocone-array[13] and hollow-NiO microspheres [14] showed attractive electro-chemical performance. However, its large volume expansion/con-traction associated with the Li-insertion and extraction processlead to electrode pulverization and loss of interparticle contact andconsequently, results in a large irreversible capacity loss and poorcycling stability.
ll rights reserved.
ry, Quaid-e-Azam University,12077395.
ansar Abbas), drsa54@yahoo.
To alleviate the above problem and further enhance thestructural stability, hybridizing NiO with carbon nanotubes (CNTs)is an effective method to accommodate the strain of volumechange during lithium insertion/extraction processes. CNTs arepromising support materials for anchoring well-dispersed nano-particles because of their unique one-dimensional tubular struc-ture, favorable electrical conductivity, high specific surface areaand excellent structural flexibility [15–17]. Consequently, we havereasons to expect that for NiO/CNT nanocomposite, nanoscale Nihas the possibility to facilitate the decomposition of Li2O and thesolid electrolyte interface (SEI) film during the charging processwhile net-structured CNTs can prevent the pulverization duringthe charge/discharge cycle and improve the conductivity.
In this work, a new hybrid nanocomposite consisting of NiOand CNTs is prepared as an anode material for LIBs. Compared toNiO nanopowder, high performance is achieved for NiO/CNTnanocomposite as LIB anode.
2. Experimental
The CNTs used in this work were prepared by our patentedtechnology (Patent number:US2009208403) using chemical vapordeposition (CVD) and were functionalized by UV/O3 treatment. Forfunctionalization, CNTs were initially exposed to UV for 1 hfollowed by 10 min ozone exhaust at room temperature andpressure [18].
Fig. 1. XRD patterns of (a) NiO (b) NiO/CNT nanocomposite (c) RBS spectra of NiO/CNT nanocomposite (d) FT-IR spectra of CNTs (e) NiO and (f) NiO/CNT nanocomposite.
Fig. 2. SEM image of (a) CNTs (b) NiO (c) NiO/CNT nanocomposite and (d) TEM image of NiO/CNT nanocomposite.
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As-obtained CNTs (0.1 g), and 0.5 g NiNO3 �6 H2O weresuccessively added into 100 mL PVP solution under constantstirring at room temperature. After being stirred for 20 min,the suspension was sonicated for 2 h. To the resulting mixture,several drops of ammonia solution (5 M) were added underultrasonic agitation to adjust the pH around 10–11. The pre-cipitates formed were separated by filtration, washed withdistilled water for six times, and then dried at 80 1C for 12 h.The final NiO/CNT nanocomposite was obtained by annealingin Ar at 450 1C for 2 h. For comparison pure NiO was alsoprepared by the same procedure.
Characterization: The samples were characterized with XRD(Bruker, D8 with CuKα radiation), SEM (JEOL, JSM5910), TEM (JEOL,JM2100) and FT-IR (NiCOLET6700). The contents of NiO/CNT nano-composite were determined using Rutherford backscattering spec-troscopy (RBS, Pelletron5UDH-2). The electrochemical tests werecarried out on CR2032 coin cells assembled according to Ref [15].
3. Results and discussion
Fig. 1a, b shows XRD pattern of the NiO and NiO/CNT nanocom-posite. NiO can be well indexed in cubic phase which accord withJCPDS No.47-1049. The peak at 2θ¼25.01 can be assigned to (002) ofthe hexagonal carbon in CNTs (JCPDS No.26-1079). The main diffrac-tions (111), (200) and (220) for NiO become broader for NiO/CNTnanocomposite, indicating its small crystallite size. Calculated withthe Scherrer equation, the average crystallite size is 32 nm.
The RBS pattern (Fig. 1c) confirms the composition ofsamples, by matching scattered energies to known scatteringcross-sections, revealing that the molar ratio of elements isalmost in agreement with the experimental concentrations.
FT-IR spectra of CNTs, NiO and NiO/CNT nanocomposite areshown in Fig. 1d–f. Upon oxidation of CNTs, the representativepeaks confirm the presence of the functional groups containingoxygen in carbon frameworks, which include the bands at,
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920 cm−1 (–OH groups bending), 1735 cm−1 (CQO stretching ofcarbonyl and carboxyl groups) and 3411 cm−1 (O–H stretching).In contrast, most absorption peaks related to oxidized groupsbecome lower in the FT-IR spectrum of nanocomposite, as theresidual oxygenated groups make it possible for NiO nanoparticlesto be firmly bonded to the surface of CNTs through covalent bondbetween Ni and oxygen. The stretching vibration of Ni–O bondappears at 415 and 563 cm−1 [19].
Fig. 2 shows the morphologies of the CNTs, NiO and NiO/CNTnanocomposite. The pristine-CNTs show a smooth outer surface withdiameters around 20–30 nm. From the SEM image (Fig. 2c), theinteraction of CNTs with NiO is excellent. The TEM observation(Fig. 2d) further reveals that NiO nanocrystals are uniformlyanchored and directly grow on the CNTs surface. The particle sizeof pure NiO is around 41 nm which decreases to 32 nm in NiO/CNTnanocomposite.
site and (d) cycling performances of CNTs, NiO and NiO/CNT electrodes.
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Electrochemical performance of CNTs, NiO and NiO/CNT nano-composite anode is presented in Fig. 3. As shown in Fig. 3a, noapparent voltage-plateau is observed for CNTs. For NiO/CNT electrode(Fig. 3c), two plateaus and a sloping potential range during the firstdischarge/charge are clearly observed. In the first cycle, a fastpotential drop to 0.84 V during discharge may result from initialreduction of NiO while a well-defined voltage-plateau at 2.2 Vreflects the Li+ charge reaction: NiO+2Li++e−-Ni (0)+Li2O [6]. Thesloping part at the end of the discharge curve between 0.84 and0.01 V, matching the plateau at 1.6 V during charge is attributed tothe formation and dissolution of SEI, respectively and the reversiblereaction between lithium and carbon structures 2C+Li++e−2LiC2[6]. From the second discharge/charge curves the plateaus are notclear though their potential-hysteresis becomes small which indi-cates that the reaction becomes more reversible. The initial specificdischarge/charge capacity is 962/849 mA h g−1 at a current density of100 mA g−1, which is higher than the theoretical capacity of NiO(718 mA h g−1). This can be attributed to the initial irreversiblereduction of NiO and formation of SEI, which is not included in thetheoretical capacity of NiO. Moreover, the NiO/CNT anode exhibits anoutstanding cycle performance. As shown in Fig. 3d, it retains acapacity of 601/482 mA h g−1 with high coulombic efficiency of 80.1%after 50 cycles, corresponding to 83.7% of the theoretical capacity ofpure NiO. The obtained capacity is comparable to some of the earlierreports on NiO based anodes, as shown in Table 1 [6,9–14,20–23].Compared with these previous reports, the present study utilizes arelatively simple synthesis approach. For NiO electrode, the first cycledischarge/charge capacity of 595/449mA h g−1 drop quickly andremain only 315/216 mA h g−1 after 30 cycles.
This high capacity in the present work comes from thenanosizes and unique structure of NiO/CNT nanocomposite.Nanoscale size provide short diffusion length for Li+-ions whileCNTs with web-like structure let electrolyte into inner regions ofthe electrode for smooth electronic connection and help accom-modate any volume changes during cycling to alleviate thepulverization.
4. Conclusions
In summary, the ultrafine NiO crystals with average size ofabout 32 nm are uniformly anchored onto the surface of CNTs to
form NiO/CNT homogeneous nanocomposite by a modified co-precipitation process. When evaluated as electrode material forLIBs, the NiO/CNT nanocomposite exhibit good electrochemicalperformance with high capacity, enhanced cycle life (962 mA h g−1
after first cycle, 601 mA h g−1 after 50 cycles) due to their nanosize,hexagonal appearance and good dispersity. Our results demon-strate that the NiO/CNT nanocomposite is a promising anodematerial for high performance LIBs.
Acknowledgments
This work is supported by the Higher Education Commission(HEC) of Pakistan.
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