Engineering calcium-doped Na3SbS4 with enhanced ion transport and interfacial compatibility for all-solid-state sodium-sulfur batteries

All-solid-state Na-S batteries (ASSNSBs) are promising candidates for grid-scale energy storage owing to their high energy density and intrinsic safety. However, the practical utilization of Na 3 SbS 4 (NSS) as a solid electrolyte is hindered by its limited intrinsic Na + transport capability. Drawing on insights from first-principles analysis of aliovalent doping and vacancy formation, we design and synthesize Ca-doped NSS electrolytes with enhanced ionic conductivity and improved compatibility with Na 3 Sn alloy anodes. The optimized Na 2.9 Ca 0.05 SbS 4 (NCSS-0.05) achieves a room-temperature ionic conductivity of 0.51 mS cm −1 and a reduced activation energy of 0.237 eV, alongside highly stable symmetric cell cycling for over 400 h. When incorporated into ASSNSBs, NCSS-0.05 enables an initial discharge capacity of 1601 mAh g −1 at 0.17 A g −1 and maintains 97.2 % capacity retention over 250 cycles at 0.5 A g −1 . Moreover, the Ca-modified electrolyte exhibits strong compatibility with various sulfide-based cathodes, including TiS 2 and VS 2 , further demonstrating its broad applicability. These results establish a robust aliovalent-doping strategy for engineering fast-ion-conducting sulfide solid electrolytes and advancing high-performance all-solid-state sodium battery technologies.