Harnessing Anion Perturbation for Self‐Limiting Decomposition for Durable Argyrodite‐Based Solid‐State Lithium Metal Batteries

ABSTRACT Argyrodite‐type electrolytes Li 6‐a PS 5‐a X 1+a (LPSX, X = Cl, Br) are attractive for All‐solid‐state lithium metal batteries (ASSLMBs) due to their high ionic conductivity and processability, yet their inherent chemical instability with Li metal causes interfacial degradation. Conventionally, this has been tackled by suppressing electrolyte decomposition. Herein, we harness controlled decomposition to construct a protective interphase. Fluorozirconate incorporation induces localized anion perturbation of PS 4 3− , which directs the initial reductive decomposition toward rapid formation of a self‐limiting solid electrolyte interphase (SEI). Theoretical calculations and experimental results reveal that the strong electron‐withdrawing character of fluorozirconate redistributes the electronic environment of adjacent PS 4 3− , making interfacial sites preferentially active and enhancing reduction susceptibility. The resulting interphase is rich in Li 2 S/Li x P and F‐containing species which is mechanically robust and electronically insulating and effectively facilitates charge transfer, thereby suppressing continuous electrolyte decomposition. Li||Li cell with optimized electrolyte can cycle steadily for 7000 h at 0.5 mA cm −2 and 0.5 mAh cm −2 . Furthermore, the full cell can retain 81.3% of its capacity after 1200 cycles at 1 C. The anion‐perturbed electrolyte delivers excellent ultra‐long cycling stability, which provides a facile regulation strategy for interfacial modification and performance optimization of ASSLMBs.