The effect of Al2O3-coating coverage on the electrochemical properties in LiCoO2 thin films

The electrochemical properties of nanoscale Al2O3-coated LiCoO2 thin films were examined as a function of the coating coverage. Al2O3-coated LiCoO2 films showed enhanced cycle-life performance with increasing degree of coating coverage, which was attributed to the suppression of Co dissolution and F− concentration in the electrolyte. Moreover, an Al2O3-coating layer with partial coverage clearly improved the electrochemical properties, even at 60 °C or with a water-contaminated electrolyte. Even though metal-oxide coating on LiCoO2 has been actively investigated, the mechanisms of nanoscale coating have yet to be clearly identified. In this article, surface analysis suggested that the Al2O3-coating layer had transformed to an AlF3∙3H2O layer during cycling, which inhibited the generation of HF by scavenging H2O molecules present in the electrolyte.