Nanoscale Observation of the Electronic and Local Structures of LiCoO2 Thin Film Electrode by Depth-Resolved X-ray Absorption Spectroscopy

The electronic and local structural changes during electrochemical delithiation processes occurring at the electrode/electrolyte interface of LiCoO2 thin film electrode prepared by pulsed laser deposition were clarified by using depth-resolved X-ray absorption spectroscopy technique. We successfully obtained detailed microstructural information around the Li1–x CoO2 electrode surface with a depth resolution of ca. 3 nm using a spectro-electrochemical cell. Our results revealed a remarkable increase in the local distortions at the Li1–x CoO2 surface after charging, and the distortions extended to the bulk of Li1–x CoO2. Such unprecedented local distortions might be attributable to the marked deterioration of the electrodes.