Interfacial engineering for all-solid-state lithium-sulfur batteries: Mechanisms, strategies, and pathways to commercialization

All-solid-state lithium‑sulfur batteries (ASSLSBs) present a paradigm-shifting opportunity for next-generation energy storage, offering ultrahigh theoretical energy density, intrinsic safety, and complete suppression of the polysulfide shuttle effect. Nevertheless, their practical realization is critically impeded by a multitude of interfacial challenges inherent to solid–solid contact architectures. This review systematically examines these multi-scale interfacial issues across four key domains: the anode/solid-state electrolyte interface, where parasitic reactions and lithium dendrite growth prevail; internal grain boundaries (GBs) within polycrystalline electrolytes, which introduce substantial ionic resistance and preferential pathways for dendrite propagation; the cathode/electrolyte interface, characterized by chemo-mechanical degradation stemming from significant volume fluctuations during cycling; and the triple-phase boundaries among active materials, conductive additives, and electrolytes, where inefficient charge transport and side reactions severely constrain sulfur utilization. Corresponding optimization strategies are comprehensively consolidated, including protective interlayer design, grain boundary engineering, cathode architecture modification, and three-phase interface regulation. Furthermore, commercialization bottlenecks are critically assessed, encompassing scalable synthesis, electrode fabrication, and cell assembly. Finally, future research directions are proposed, emphasizing integrated multi-scale engineering, advanced in-situ characterization, and industrialization-oriented manufacturing to bridge the gap between fundamental research and practical deployment.