Sulfur-Enabled Structural Amorphization and Operando Interfacial Densification in Halide-Based Solid Electrolytes for Long-Lasting All-Solid-State Sodium Batteries

All-solid-state sodium batteries (ASSBs) offer advantages of high safety and low cost, making them promising for next-generation energy storage. However, their development is primarily limited by the low ionic conductivity of solid electrolytes owing to the sluggish kinetics of Na+ ions. Here, we report an amorphous solid electrolyte, 0.75Na2S–TaCl5, via incorporating S2– into the chloride sublattice. The mixed-anion sublattice promotes amorphization, eliminating grain boundaries and creating an isotropic ion transport network, which delivers a room-temperature ionic conductivity of 1.38 mS cm–1. More importantly, the soft amorphous electrolyte enables an unprecedented electrochemically driven densification process that progressively heals voids and microcracks during cycling, which actively improves the electrode–electrolyte contact. This self-healing behavior allows ASSBs to achieve stable cycling over 1400 cycles at 0.3C and over 3500 cycles at 1C under ambient conditions. This work demonstrates that the disordered atomic arrangement in an amorphous electrolyte can simultaneously improve ion transport and enhance interfacial properties.