Superionic Amorphous NaTaCl6 Halide Electrolyte for Highly Reversible All-Solid-State Na-Ion Batteries

Designing Na-ion solid electrolytes (SEs) of high ionic conductivity and excellent chemical/mechanical compatibility with cathode materials remains challenging for all-solid-state Na-ion batteries (ASSNIBs). In this study, we successfully designed and synthesized a novel amorphous NaTaCl6 halide SE with unprecedented ionic conductivity of 4 x 10-3 S cm-1 at room temperature, surpassing any previous results in the Na-ion halide SE community. The achieved outstanding ionic conductivity can be attributed to the formation of reconstructed amorphous poly-(TaCl6) octahedra network triggered by high-energy mechanochemical reactions, which effectively repels Na+ ions with weakened Na-Cl interactions into the open amorphous halide matrix. Notably, the amorphous NaTaCl6 halide SE demonstrates good mechanical deformability as well as impressive chemical/electrochemical stability, leading to a remarkable initial Coulombic efficiency (ICE) of up to 99.60%, excellent rate performance with 85% capacity retention at 2 C, and stable long-cycling profiles with 81%/95%/100% capacity retention after 4000/600/800 cycles at 3/1/0.5 C when coupled with Na3V2(PO4)3 cathodes in ASSNIBs. To the best of our knowledge, the integrated electrochemical performance of ASSNIBs in this work represents the best result reported in the literature. The discovery of superionic amorphous Na-ion halide SEs offers a promising avenue for the development of high-performance ASSNIBs.