Nanoscale Observation of the Electronic and Local Structures of LiCoO<sub>2</sub> 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 LiCoO<sub>2</sub> 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 Li<sub>1–<i>x</i></sub>CoO<sub>2</sub> 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 Li<sub>1–<i>x</i></sub>CoO<sub>2</sub> surface after charging, and the distortions extended to the bulk of Li<sub>1–<i>x</i></sub>CoO<sub>2</sub>. Such unprecedented local distortions might be attributable to the marked deterioration of the electrodes.