Interface characterization of MgF2-coated LiCoO2 thin films

The electrochemical properties and interface reactions of pristine and coated LiCoO2 films were characterized. MgF2 was used as a new coating material to improve the electrochemical properties of the LiCoO2 film electrode. To directly observe the interface reaction between the surface of the cathode and the electrolyte, a film electrode with a wide, flat surface was introduced in this study. The rate capability, cyclic performance, and stability at high temperature of the LiCoO2 thin film were improved by MgF2 coating. The concentration–depth profile and surface image of the LiCoO2 film were investigated by SEM and XPS analyses before and after cycling. Pristine film showed significant Co dissolution and surface damage on cycling at high temperature (45 °C). However, both were efficiently depressed by the introduction of the MgF2 coating. These results confirm that the MgF2 coating layer successfully protected the surface of the cathode from the reactive electrolyte, leading to enhanced electrochemical properties for MgF2-coated LiCoO2 films.