Solid Catholyte with Regulated Interphase Redox for All‐Solid‐State Lithium‐Sulfur Batteries

All-solid-state lithium-sulfur battery (ASSLSB) is considered one of the ultimate next-generation energy storage technologies due to the expected low cost, high safety, and high specific energy. The high-conductivity and low-modulus sulfide electrolytes hold promise as electrolytes in the cathode (i.e., solid catholytes) for ASSLSBs, but their parasitic decomposition and reactions over cycling lead to degradation of the active material-catholyte interphases and hence limited cycling life. Herein a strategy is described to stabilize the ASSLSBs by regulating the interphase redox reversibility of the sulfide catholyte, which is validated on a new sulfide electrolyte formulated as Li_6+xP_1-xW_xS₅I (LPWSI). The experiments show that the presence of mixed ionic-electronic conducting WS₂ boosts the Li₄P₂S₇-to-Li₃PS₄ reaction in the interphase, which prevents irreversible accumulation of impeding P₂S₇ ^4- and thereby improves the catholyte's interphase stability. With the LPWSI catholyte, the ambient-temperature ASSLSB exhibits stable cycling sustaining 92.2% capacity over 400 cycles at C/5 with an initial areal capacity of 1.95 mA h cm^-2. Furthermore, the cells demonstrate excellent high-rate stability over 1000 cycles at rates of 1C and 2C. The reported strategy contributes to reshaping the understanding of how solid catholyte can function in composite cathodes and provides new guidelines for designing catholyte for high-capacity conversion-based electrodes that involve complex evolution of interphases.