Comparative studies have been carried out to understand the improvement mechanism of surface modification on naked and surface-modified LiCoO2 by Raman and X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It is shown that surface coating cannot prevent the dissolution of lithium from LiCoO2 in the electrolyte solvent and its structural degradation at room temperature. Rather, modifying the surface of commercial LiCoO2 particles can suppress the formation of oxygen with higher oxidizing power and alleviate the electrolyte decomposition at charged states. (C) 2004 Elsevier B.V. All rights reserved.