Suppression of interface reaction of LiCoO2 thin films by Al2O3-coating

Al2O3-coated LiCoO2 thin films were prepared to characterize the effects of coating in detail. The LiCoO2 film electrodes served as effective pristine cathodes to investigate the interface reaction between a cathode and electrolyte because they have wide and smooth surface and do not contain conducting agents (such as carbon) or binders. The electrochemical properties, surface morphology, and concentration profile (vs. depth) were characterized to identify the effects of coating. The Al2O3-coated film showed a much improved rate capability and cyclic performance compared with those of the pristine film. Specifically, based on the results of SIMS analyses and SEM images, dissolution of transition-metal ions and surface damage during storage at high temperature were suppressed by Al2O3 coating. This result directly shows the successful protective effect of surface coating, which is associated with enhanced electrochemical properties of the coated film.