Stable Catholyte Interface Enables Practical Operation of Sulfide‐Based All‐Solid‐State Li Metal Batteries

Abstract Achieving chemical and electrochemical stability of sulfide‐based solid electrolytes is crucial for enabling practical slurry fabrication and reliable operation of all‐solid‐state batteries (ASSBs). Herein, a fluorocarbon‐terminated self‐assembled monolayer (SAM) strategy is reported that forms a conformal and chemically inert surface on Li 6 PS 5 Cl (LPSCl), yielding a stabilized catholyte (─CF 3 @LPSCl) compatible with polar solvent‐based processing. The SAM layer effectively suppresses nucleophilic degradation induced by ester solvents and moisture while maintaining the crystalline bulk structure and high ionic conductivity of LPSCl. The surface fluorination simultaneously enhances both chemical and electrochemical stability, characterized by X‐ray absorption near‐edge structure measurements, enabling high‐rate capability and stable cycling under 1.0 C conditions. Under low stack pressure (≈0.3 MPa), the ─CF 3 @LPSCl catholyte suppresses not only the catholyte degradation but also alleviates mechanical contact loss within the cathode, achieving superior cycling stability without reliance on binder reinforcement. Notably, full cells assembled with thin Li metal and a low N/P ratio exhibit 90.5% capacity retention over 300 cycles. This work demonstrates that a simple but straightforward fabrication of surface‐stable catholyte—beyond binder and electrode engineering—can play a decisive role in achieving scalable and pressure‐tolerant ASSBs platforms.