Toward practical all-solid-state lithium-sulfur batteries: from reaction mechanisms to engineering strategies

All-solid-state lithium-sulfur batteries (ASSLSBs) are regarded as a promising high-energy-density energy-storage platform with improved safety potential because the use of solid electrolytes can substantially suppress polysulfide dissolution and shuttle effects commonly encountered in conventional liquid-electrolyte Li-S systems. However, replacing liquid electrolytes with solid-state electrolytes alters sulfur reaction pathways, charge-transport modes, and interfacial physics, introducing additional challenges for achieving high performance. This review first analyzes the critical issues associated with sluggish solid-state sulfur conversion chemistry that limit the practical application of ASSLSBs, including Li₂S₂ intermediates, reaction overpotentials, and Li₂S nucleation and growth behavior. Building on this understanding, we critically discuss how three-phase-boundary-limited charge transfer and mixed ion-electron transport govern sulfur utilization and rate capability. We then systematically review recent advances in cathode architecture, solid electrolyte design, and interfacial engineering, including mixed conductors, catalytic and redox-mediated sulfur conversion, and halide-modified solid electrolytes, with emphasis on their roles in enhancing reaction kinetics, interfacial stability, and chemo-mechanical compatibility. Finally, key engineering challenges toward practical ASSLSBs, such as high sulfur loading, ultrathin solid electrolyte membranes, and low-pressure operation, are evaluated. By integrating reaction mechanisms, interfacial physics, and device-level constraints into a unified framework, this review aims to clarify the governing principles, highlight viable development pathways, and provide guidance for the rational design of next-generation high-energy ASSLSBs.