Effects of ZrO2 Coating on LiCoO2 Thin-Film Electrode Studied by In Situ X-ray Absorption Spectroscopy

Surface modification effects on interfacial reaction for zirconia (ZrO2) coated lithium cobalt oxide (LiCoO2) are studied. ZrO2-coated LiCoO2 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 ZrO2 coating. AC impedance spectroscopy reveals that there are two types of resistance associated with ZrO2 coating; one Is the charge transfer resistance which depends on the Li+-containing electrolyte concentration, and the other is the ZrO2-layer resistance which depends on the deposition periods of ZrO2 coatings. In situ total-reflection fluorescence X-ray absorption spectroscopy for ZrO2-coated LiCoO2 thin-film electrodes reveals that the ZrO2 coating layer suppresses the reduction reaction by electrolyte contact, leading to improving its cycle performance. Depth-resolved X-ray absorption spectroscopy reveals that the ZrO2 coating layer can prevent the increase of local distortion of the LiCoO2 electrode when overcharged, leading to high-potential durability. (C) 2013 The Electrochemical Society.