Mitigating Contact Loss in Li₆PS₅Cl‐Based Solid‐State Batteries Using a Thin Cationic Polymer Coating on NCM

Abstract Thiophosphate‐based solid‐state batteries (SSBs) with high‐nickel ternary cathode materials such as LiNi_0.83Co_0.11Mn_0.06O₂ (NCM) represent a promising next‐generation energy storage technology due to their expected high specific discharge capacity and improved safety. However, rapid capacity fading caused by contact loss through interphase and crack formation during cell cycling is a significant problem hindering stable SSB cycling and high‐energy‐density applications. In this work, a uniform coating of poly((4‐vinyl benzyl)trimethylammonium bis(trifluoromethanesulfonylimide)) (PVBTA‐TFSI) on NCM is obtained via a spray‐drying process. This exceptionally thin cationic polymer coating of only 2–4 nm thickness on NCM helps stabilize the interface between NCM and the Li₆PS₅Cl solid electrolyte (SE). Electrochemical tests confirm a significant improvement in long‐term cycling performance and active mass utilization compared to uncoated NCM. In addition, the polymer coating effectively suppresses the degradation of the NCM/SE interface, particularly the formation of oxygenated species, and reduces the extent of particle cracking. Overall, these results highlight a new approach to mitigate SSB degradation using a thin cationic polymer coating on NCM for SSBs.