Characterization and preparation of NiO-V2O5 composite film cathodes

NiO-V2O5 composite films have been fabricated by 355 nm pulsed laser reactive deposition using mixed metallic Ni and V targets with different molar ratios. The optimal deposition conditions of NiO-V2O5 composite films are found to be the substrate temperature of 300 degreesC and 100 mTorr O-2 ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses showed that the crystallinity of the NiO-V2O5 composite films gradually decreased with increasing the amount of nickel oxide and transformed to amorphous phase as the molar ratio of NiO/V2O5 (x) approaches 0.5. The amorphous (NiO)(0.5)V2O5 composite film electrode exhibited a specific capacity of 340 mAh/g at a discharge rate of 2 C upon cycling with no obvious fading up to 500 cycles. XRD and X-ray photo-electron spectroscopy (XPS) measurements of NiO-V2O5 composite film electrodes revealed that there exists two electrochemical processes upon cycling. During the first discharge, the Li ions insertion process is accompanied by the reduction of NiO into metallic Ni. Then, the reversible processes involving Li ions insertion/extraction in V2O5 matrix and oxidation/reduction of Ni and Li2O take place upon the subsequent cycling. (C) 2003 Elsevier B.V. All rights reserved.