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.