Unraveling the Degradation Mechanism of LiNbO₃‐Coated NCM Cathode at High Potential in All‐Solid‐State Batteries Using 10 K Extended X‐ray Absorption Fine Structure Analysis

Abstract All solid‐state batteries (ASSBs) utilizing sulfide‐based solid electrolytes hold promise for enhancing battery energy density while mitigating safety concerns, thus meeting the stringent requirements for electric vehicle applications. For the practical application of ASSBs, it is important to stabilize the interface between the solid electrolyte and the cathode. Although cathode coated with a thin layer of LiNbO₃ provide higher interface stability, which significantly improves charge‐discharge and cycle performance, degradation at high potentials has also been noted. In this study, we focused on the degradation mechanism of LiNbO₃‐coated LiNi_0.5Co_0.2Mn_0.3O₂ cathode active materials at high potentials by using three electrode system for ASSBs, which allows separating the impedance measurement of the interface between cathode and solid electrolyte. We performed X‐ray absorption spectroscopy (XAS) measurements at low temperature (10 K) to analyze the local structure around Nb and correlate these findings with impedance measurements. Our results indicate that the impedance of LiNbO₃ increased rapidly due to the oxygen desorption reaction at high potentials. This study aims to elucidate the dynamic changes and degradation mechanism of LiNbO₃‐coated LiNi_0.5Co_0.2Mn_0.3O₂ in ASSBs and provide new ideas for the design of interfacial coating materials.