Bulk Na + Transport and Interfacial Stability in Inorganic Solid Electrolytes for All-Solid-State Sodium-Metal Batteries

All-solid-state sodium-metal batteries (ASS-SMBs) are promising for safe, sustainable energy storage, but their advancement requires solid electrolytes that combine fast bulk Na + transport with stable interfaces, two factors that are intrinsically coupled. This review presents a descriptor-based perspective on sodium-ion conduction across major inorganic electrolyte families, including oxides, sulfides, halides, anti-perovskites, and complex hydrides. We emphasize how crystal structure, defect chemistry, lattice dynamics, and grain-boundary characteristics govern migration pathways, transport heterogeneity, and interfacial evolution. We then examine the origins of key interfacial challenges, such as space-charge effects, contact loss, interphase instability, and dendrite initiation and relate them to bulk transport descriptors across different electrolyte systems. Finally, we summarize current design and interface-engineering strategies and propose cross-family design rules for developing practical inorganic solid electrolytes for ASS-SMBs.