Halide as Catholyte in Composite Cathode to Enhance Cycling Stability of All-Solid-State Lithium–Sulfur Batteries

All-solid-state lithium–sulfur batteries (ASSLSBs) using inorganic solid-state electrolytes can effectively alleviate the polysulfide shuttle effect in liquid electrolytes and improve the energy density. However, the electrochemical window of sulfide-based catholytes in composite cathodes is relatively narrow, which makes the evaluation of electrochemical performance of sulfur cathodes in ASSLSBs complicated. The decomposition of the sulfide catholytes increases the interfacial resistance, thus reducing the battery cycle life. To overcome these challenges, Li3YCl5I has been developed with a wide window of electrochemical stability for a catholyte suitable for a composite cathode. Its ionic conductivity is as high as 1.67 × 10–3 S cm–1, which is conducive to the rapid transport of lithium ions. The ASSLSB based on the Li3YCl5I catholyte exhibits a discharge specific capacity of 1084.05 mAh g–1 at 45 °C. Additionally, it maintains 81.5% capacity after 100 cycles, significantly exceeding the retention rate of 54.5% for a battery using Li6PS5Cl.