NaTaCl6: Chloride as the End-Member of Sodium-Ion Conductors

All-solid-state sodium batteries are beneficial owing to their high energy density, safety, and abundance. Solid electrolytes are key materials in the improvement of the construction and performance of batteries. Chloride-based solid electrolytes are particularly important for achieving high energy densities, owing to their high oxidation stability, ionic conductivity, and formability. Herein, the development of a chloride-based sodium-ion conductor NaTaCl6 is reported as a new end-member. The NaTaCl6 prepared using the mechanochemical method exhibits an ionic conductivity of 6.2 × 10–5 S cm–1 at 25 °C, which is among the best reported systems of end-members of chloride-based sodium-ion conductors. We demonstrated a 3.3 V all-solid-state cell with the NaTaCl6 electrolyte. The discovery of fast sodium-ion-conducting chloride-based end-member NaTaCl6 with high oxidation stability has boosted the ongoing development of halide-based sodium-ion conductors and solid-state rechargeable batteries.