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

Thiophosphate‐based solid‐state batteries (SSBs) with high‐nickel ternary cathode materials such as LiNi0.83Co0.11Mn0.06O2 (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. Cell cycling‐induced passivation layer formation and LiNi0.83Co0.11Mn0.06O2 NCM particles cracking hinder lithium transport and cause contact loss, leading to active mass loss. This study introduces a poly((4‐vinyl benzyl)trimethylammonium bis(trifluoromethanesulfonylimide)) (PVBTA‐TFSI) coating on NCM surfaces for mitigating solid‐state battery degradation mechanisms.