Highly Conductive Halide Na-ion Conductor Boosted by Low-cost Aliovalent Polyanion Substitution for All-Solid-State Sodium Batteries

Halide-based Na-ion conductors have attracted intense attention due to their great compatibility with oxide cathodes. However, zirconium (Zr)-based halide solid electrolytes (SEs) suffer heavily from poor ionic conductivity that hinders their application in all-solid-state batteries (ASSBs). Herein, we employ soda ash (Na ₂ CO ₃ ) as a low-cost precursor and introduce an aliovalent polyanion to produce a novel family of (2- x )NaCl- x Na ₂ CO ₃ -ZrCl ₄ compounds to realize superior Na-ion conductivity. With the optimal mole ratio, the highest ionic conductivity (1.02 mS cm ^− 1 ) at room temperature is achieved due to the presence of amorphous phase. Meanwhile, this NaCl-Na ₂ CO ₃ -ZrCl ₄ compound also exhibits impressive electrochemical stability and mechanical properties. Pairing with NaCrO ₂ as cathode, the assembled ASSBs deliver an initial discharge capacity of 117 mAh g ^− 1 at 0.1 C and demonstrate a long-term cycling stability at 0.3C for 850 cycles. This work highlights a novel halide-based SE design and contributes to developing ASSBs with high electrochemical performance.