Organic‐Additive‐Derived Cathode Electrolyte Interphase Layer Mitigating Intertwined Chemical and Mechanical Degradation for Sulfide‐Based Solid‐State Batteries

Abstract Keeping both the chemical and physical state of the electrode–electrolyte interface intact is one of the greatest challenges in achieving solid‐state batteries (SSBs) with longer cycle lives. Herein, the use of organic electrolyte additives in the cathode electrolyte interphase (CEI) layer to mitigate the intertwined chemical and mechanical degradation in sulfide‐based SSBs is demonstrated. Lithium difluorobis(oxalato)phosphate (LiDFBOP) and argyrodite (Li₆PS₅Cl) are used as a model system, with the LiDFBOP‐derived CEI layer induced by irreversible oxidation above 4.12 V (vs Li⁺/Li) during the formation cycle exhibiting dual functions. This CEI layer retards the rate of chemical degradation between the cathode active particles and solid electrolytes at high charging potential and helps maintain intimate physical contact even at a low stack pressure of 0.75 MPa. The improved physical contact enables delivery of a high initial capacity, while chemical stability suppressing the sulfite or sulfate formation has a more dominant effect on the long‐term cycle stability. This study presents a new perspective and strategies for designing cathode coating materials for sulfide‐based SSBs beyond the typically used inorganic oxide materials.