Progress and Prospects of Solid-State Electrolytes in Metal–Sulfur Batteries

Metal–sulfur (M-S) batteries, including lithium–sulfur (Li–S), sodium–sulfur (Na–S), zinc–sulfur (Zn–S), and magnesium–sulfur (Mg–S), combine very high theoretical capacities with low active-material cost and minimal reliance on transition metals. Their practical deployment is still limited by polysulfide dissolution, poor cathode conductivity, large volume change, and dendrite formation at metal anodes. This review focuses on solid-state electrolytes (SSEs) based on inorganic ceramics, polymers, and hybrid frameworks that are being developed to address these issues. We adopt an interphase-centered, problem-solving perspective and discuss how SSE ionic transport, interfacial chemistry, and mechanical properties jointly control polysulfide confinement, sulfur utilization, volume-change accommodation, and metal-anode stability. By comparing representative systems, we extract design rules for composite architecture and interface engineering. Remaining challenges, including modest room-temperature conductivity, interfacial resistance, brittleness, and scalable processing, are highlighted, and future research directions are outlined for safe, high-energy-density M-S batteries.