Effects of ZrO₂Coating on LiCoO₂Thin-Film Electrode Studied by In Situ X-ray Absorption Spectroscopy

Surface modification effects on interfacial reaction for zirconia (ZrO 2 ) coated lithium cobalt oxide (LiCoO 2 ) are studied. ZrO 2 -coated LiCoO 2 thin-film electrodes are prepared by a pulsed laser deposition with different preparation periods. Cyclic voltammetry measurements clearly show that cycle performance and high-potential durability are improved by the ZrO 2 coating. AC impedance spectroscopy reveals that there are two types of resistance associated with ZrO 2 coating; one is the charge transfer resistance which depends on the Li + -containing electrolyte concentration, and the other is the ZrO 2 -layer resistance which depends on the deposition periods of ZrO 2 coatings. In situ total-reflection fluorescence X-ray absorption spectroscopy for ZrO 2 -coated LiCoO 2 thin-film electrodes reveals that the ZrO 2 coating layer suppresses the reduction reaction by electrolyte contact, leading to improving its cycle performance. Depth-resolved X-ray absorption spectroscopy reveals that the ZrO 2 coating layer can prevent the increase of local distortion of the LiCoO 2 electrode when overcharged, leading to high-potential durability.