NaCl interphase enables stable Na_2.85Sb_0.95W_0.05S_3.9Cl_0.1-based all-solid-state sodium batteries

All-solid-state sodium (Na) batteries (ASSSBs) have attracted considerable attention due to their inherent safety and low cost. Developing sodium sulfide electrolytes with high Na⁺ ionic conductivity and excellent stability in contact with sodium metal anodes is crucial to realize high-performance ASSSBs. Herein, a tungsten (W) and chlorine (Cl) co-doped Na_2.85Sb_0.95W_0.05S_3.9Cl_0.1 solid electrolyte is effectively prepared through melt-quenching combined with a subsequent annealing process. Through W-Cl co-doping, Na vacancies are introduced into the Na₃SbS₄ electrolyte, thereby enhancing the ionic conductivity from 0.92 mS cm^-1 to 12.66 mS cm^-1. Meanwhile, the in situ formed NaCl-based electronically insulating interphase layer between Na_2.85Sb_0.95W_0.05S_3.9Cl_0.1 and the sodium metal effectively suppresses interfacial side reactions and improves interfacial stability. The obtained Na/Na_2.85Sb_0.95W_0.05S_3.9Cl_0.1/Na symmetric cell demonstrates stable cycling over 800 h at 0.05 mA cm^-2. Moreover, the TiS₂/Na_2.85Sb_0.95W_0.05S_3.9Cl_0.1/Na ASSSB realizes an initial charge capacity of 142.2 mAh g^-1 at 0.1C, maintaining a capacity retention of 81.6% after 100 cycles. This work presents a viable approach for designing sodium sulfide electrolytes that combine high ionic conductivity with superior stability with a sodium anode.