Enhanced Electrochemical Stability in All‐Solid‐State Lithium–Sulfur Batteries with Lithium Argyrodite Electrolyte

Lithium argyrodite electrolytes with halide dopings (Li₆PS₅X, X = Cl, Br, I) are a group of sulfide solid electrolyte materials (SSEs) widely adopted in all-solid-state lithium-sulfur batteries (ASSLSBs) for their ease of processing and low material costs. Specifically, the Cl-doped lithium argyrodite electrolytes, with the highest ionic conductivities among the halide-doped lithium argyrodite electrolytes, are extensively studied in the literature. However, their narrow electrochemical stability window limits the performance of ASSLSBs due to the inevitable electrolyte decomposition within the operating voltage window. Here, the Br-doped lithium argyrodite electrolyte (Li_5.5PS_4.5Br_1.5) is utilized as a comparison to the widely-adopted Cl-doped lithium argyrodite electrolyte (Li_5.5PS_4.5Cl_1.5) in ASSLSBs. Despite its slightly lower ionic conductivity, Li_5.5PS_4.5Br_1.5 significantly enhances the overall cell performance and cyclability of the LiIn ǁ SSE ǁ S-C-SSE cell due to a wider electrochemical stability window. With a better electrochemical stability of Li_5.5PS_4.5Br_1.5 within the working voltage range of ASSLSBs, the LiIn ǁ SSE ǁ S-C-SSE cell with Li_5.5PS_4.5Br_1.5 attains an excellent capacity retention of 90% over 100 cycles at 1.4-3.1 V and 68% over 250 cycles even at a wider voltage window of 1.1-3.1 V.