Nanoscale observation of the electronic and local structures of LiCoO ₂ 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 Li _1-xCoO₂ 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_1-xCoO₂ surface after charging, and the distortions extended to the bulk of Li _1-xCoO₂. Such unprecedented local distortions might be attributable to the marked deterioration of the electrodes.