Enhanced lithium storage in a VO2(B)-multiwall carbon nanotube microsheet composite prepared via an in situ hydrothermal process

A novel VO2(B)-rnultiwall carbon nanotube (MWCNT) composite with a sheet-like morphology was synthesized by a simple in situ hydrothermal process. The morphology and structural properties of the samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). FE-SEM observations demonstrated that the nanosheets are frequently grown together in the form of bundles composed of numerous nanosheets, each with a smooth surface and a typical length of 300-500 nm, width of 50-150 nm, and thickness of 10-50 nm. Electrochemical measurements were carried out using different discharge cut-off voltages. Electrochemical tests show that the VO2(B)-MWCNT composite cathode features long-term cycling stability and high discharge capacity (177 mAh g(-1)) in the voltage range of 2.0-3.25 V at 1 C with a capacity retention of 92% after 100 cycles. The electrochemical impedance spectra (EIS) indicate that the VO2(B)-MWCNT composite electrode has very low charge-transfer resistance compared with pure VO2(B), indicating the enhanced ionic conductivity of the VO2(B)-MWCNT composite. The enhanced cycling stability is attributed to the fact that the VO2(B)-MWCNT composite can prevent the aggregation of active materials, accommodate the large volume variation, and maintain good electronic contact. We strongly believe that the VO2(B)-MWCNT composite can be considered as a potential cathode material for lithium-ion batteries. (C) 2010 Elsevier Ltd. All rights reserved.