Comparison of electrochemical behavior of LiCoO2 thin films prepared by sol-gel and sputtering processes

The effects of crystal orientation and the presence of impurity phase on Li-ion insertion and extraction processes and oxidation behavior of propylene carbonate (PC) containing 1.0 mol dm(-3) LiClO4 were investigated by using LiCoO2 thin films prepared by the sol-gel process and rf sputtering with cyclic voltammetry, electrochemical impedance measurement, in situ Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Three kinds of LiCoO2 thin film electrodes were prepared by rf sputtering and sol-gel processes. These electrodes contained different amounts of cubic phase (Co3O4) as an impurity phase and had different crystal orientations depending on the preparation conditions. These properties greatly influenced the electrochemical behaviors and adsorption phenomena of oxidation products derived from PC. The organic surface film on LiCoO2 thin film was analyzed with XPS. This surface film formation also depended on the crystal orientation and amount of impurity involved in the LiCoO2 thin films. When the (003) plane of the LiCoO2 is more perpendicular to substrate and the thin film does not contain impurity, the best electrochemical performance can be attained. (c) 2005 The Electrochemical Society.