Enhanced Electrochemical Stability and Extended Cycle Life in Sulfide‐Based All‐Solid‐State Batteries: The Role of Li10SnP2S12 Coating on Ni‐Rich NCM Cathode

Abstract Recently, sulfide‐based all‐solid‐state batteries (ASSBs) have attracted great attention because of their excellent safety and high energy density. However, by‐products formed from side‐reactions between the oxide‐based cathodes and sulfide‐based solid electrolytes (SEs) increase the interfacial resistance and degrade the cell performance. Suppression of this interfacial resistance is thus critical. In this study, the extraordinarily high stability of the cathode/SE interface is discovered when a Li 10 SnP 2 S 12 (LSnPS) is applied to a cathode buffer layer. The electrochemical properties of the cathode interface at high potential are improved by synthesizing a core–shell structure cathode using LSnPS. The synthesized LSnPS is uniformly coated on a Li 2 ZrO 3 ‐coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 (LZO‐NCM) surface using the cost‐efficient mechano‐fusion method. The ASSB with LSnPS‐coated LZO‐NCM as the cathode and Li 6 PS 5 Cl (argyrodite, LPSCl) as the SE exhibited a capacity of 192 mAh g −1 and excellent cycle retention of ≈75% after 500 charge/discharge cycles. In addition, the degradation mechanism at the cathode/SE interface is investigated. The results indicated that LSnPS stabilizes the interface between NCM and argyrodite, thereby inhibiting the decomposition of the SE. This technology is expected to contribute to the commercialization of cathode materials for sulfide‐based ASSBs due to its enhanced cycle performance, low‐cost material application, and eco‐friendly process.