Spectroelectrochemical studies on highly polarized LiCoO₂ electrode in organic solutions

In situ Raman spectroscopy was conducted on thin film electrodes of pure LiCoO₂ in order to observe the nature of the changes in interfacial structure between LiCoO₂ and organic solutions (propylene carbonate and ethylene carbonate containing 1 M LiClO₄) when LiCoO₂ is scanned up to highly anodic potentials (~ 5.0VLi⁺/Li). Raman spectra and cyclic voltammograms were recorded simultaneously during the potential scan. We observed a sudden increase in the background signals of the Raman spectra at potentials more positive than 4.7 V. The increased background did not change after potential cycling. The change was irreversible, indicating that surface film formation occurred at positive potentials. As organic compounds fluoresce by visible light, the increased background is ascribed to the formation of a film on the LiCoO₂ electrode surface in organic solutions. (C) 2000 Published by Elsevier Science S.A.