A Surface Non‐Destructive Modification Strategy Addressing Moisture and Oxidation Instabilities of Sulfide Solid‐State Electrolytes

Sulfide solid electrolytes are promising candidates for all‐solid‐state batteries (ASSBs), owing to their high ionic conductivity and excellent interfacial conformability. However, their practical application is hindered by inherent oxidative instability and high moisture sensitivity. Herein, we propose an in situ, non‐destructive modification strategy for sulfide electrolyte Li 6 PS 5 Cl (LPSC) by leveraging the nucleophilic S 2− anions on its surface to initiate the ring‐opening polymerization of 1,3,2‐dioxathiolane 2,2‐dioxide (ethylene sulfate, DTD), thus forming a uniform and dense poly(sulfate) (PS) modification layer. This layer effectively shields the electrolyte from direct exposure to moisture and high‐voltage cathodes, greatly enhancing both moisture tolerance and oxidation stability. ASSBs fabricated with the modified PS‐LPSC electrolyte, a high‐nickel LiNi 0.9 Co 0.05 Mn 0.05 O 2 (NCM955) cathode and a LiIn anode, exhibit excellent electrochemical performance, delivering capacities of 231.6, 208.1, 138.3, and 98.5 mA h g −1 at 0.2, 1, 10, and 20 C, respectively, at room temperature. Remarkably, the cells retain 70.0% capacity after 36,000 cycles at 10 C under room temperature, and 62.4% after 20,000 cycles even under harsh conditions (50 C and 60 °C), demonstrating exceptional long‐term cycling stability and practical applicability. This study provides a facile and efficient surface modification route to enhance the oxidation and moisture stability of sulfide solid electrolytes.