Solid–Polymer–Electrolyte Interphase Inductively Formed by Surface Chemistry to Stabilize the High Ni Cathode in Sulfide‐Based All‐Solid‐State Lithium Batteries

High‐nickel cathode, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), and sulfide‐solid electrolyte are a promising combination for all‐solid‐state lithium batteries (ASSLBs). However, this combination faces the issue of interfacial instability between the cathode and electrolyte. Given the surface alkalinity of NCM811, we propose a strategy to construct a solid–polymer–electrolyte (SPE) interphase on NCM811 surface by leveraging the surface alkaline residues to nucleophilically initiate the in‐situ ring‐opening polymerization of cyclic organic molecules. As a proof‐of‐concept, this study demonstrates that the ring‐opening copolymerization of 1,3‐dioxolane and maleic anhydride produces a homogeneous, compact, and conformal SPE layer on NCM811 surface to prevent the cathode from contact and reaction with Li 6 PS 5 Cl solid‐state electrolyte. Consequently, the SPE‐modified‐NCM811 in ASSLBs exhibits high capacities of 193.5 mA h g –1 at 0.2 C, 160.9 mA h g –1 at 2.0 C and 112.3 mA h g –1 at 10 C, and particularly, excellent long‐term cycling stabilities over 11000 cycles with a 71.95% capacity retention at 10 C at 25°C, as well as a remained capacity of 117.9 mA h g –1 after 8000 cycles at 30 C at 60°C, showing a great application prospect. This study provides a new route for creating electrochemically and structurally stable solid–solid interfaces for ASSLBs.