Degradation Analysis by X-ray Absorption Spectroscopy for LiNbO3 Coating of Sulfide-Based All-Solid-State Battery Cathode

The surface coating of cathode active material in all-solid-state batteries using sulfide-based solid electrolytes is well-known to be a fundamental technology, and LiNbO₃ is one of the most representative materials. The half cells using the cathode mixture of Li₆PS₅Cl/LiNbO₃-coated LiNi_0.5Co_0.2Mn_0.3O₂ were exposed in harsh conditions at 60 °C and 4.25-4.55 V vs Li/Li⁺ and analyzed by transmission electron microscope/energy dispersive X-ray spectroscopy (TEM/EDS) and X-ray absorption spectroscopy (XAS). TEM/EDS observation shows that Nb element derived from LiNbO₃ coating had remained at the interface, which means that Nb element had not migrated to the solid electrolyte and active material. On the other hand, the XAS spectra of Nb L₃-edge changed corresponding to cell performance degradation. From the comparison with the spectra of the reference materials of the Li-Nb-O system, the XAS spectral changes were assigned to the decomposition reaction which released Li and O from the LiNbO₃ coating. The side reaction is presumed to cause to the oxidization deterioration of sulfide electrolyte at the interface of Li₆PS₅Cl/LiNbO₃-coated LiNi_0.5Co_0.2Mn_0.3O₂.