All-Solid-State Lithium–Sulfur Batteries: Recent Progress, Challenges, and Perspectives

All-solid-state lithium–sulfur batteries (ASSLSBs) couple the high theoretical energy density of sulfur (2600 Wh kg⁻¹) with the safety and polysulfide-shuttle suppression advantages of solid electrolytes (SEs). In practice, however, sluggish solid-state conversion kinetics, chemo-mechanical degradation in composite cathodes, and large solid–solid interfacial resistance remain the principal barriers to practical implementation. This review systematically examines recent progress across the three key components of ASSLSBs: cathodes, solid electrolytes, and interfaces. For cathodes, S/C composite design strategies and alternative active materials—including Li₂S, metal sulfides, and organosulfur compounds—are discussed. For solid electrolytes, inorganic (sulfide, oxide, halide, and hydride), polymer, and hybrid composite systems are compared. For interfaces, physical strategies (stack pressure, compliant interlayers, three-dimensional cathode architectures) and chemical strategies (cathode–SE and Li metal–SE interphase engineering, in situ stabilization) are evaluated. Outstanding challenges and design guidelines for next-generation ASSLSBs are discussed.