Fast Sodium-Ion Conducting Amorphous Oxychloride Embedding Nanoparticles

Developing materials with high sodium-ion conductivities is crucial for improving the electrochemical performance of all-solid-state batteries. Halide solid electrolytes are promising owing to their high conductivity, formability, and oxidation stability. However, state-of-the-art sodium-ion-conducting halides are not as high in conductivity as expected and lack reduction stability. In this study, we report oxychlorides in a ternary system NaCl–TaCl₅–Ta₂O₅ with high conductivities, formabilities, and oxidation and reduction stabilities. The mechanochemically prepared samples are composed of NaCl and Ta₂O₅ nanoparticles embedded in an Na–Ta–Cl–O amorphous matrix, possessing ionic conductivities of 2.5 × 10^–3 S cm^–1 at 25 °C and electrochemical potential windows of 0.4–4.1 versus Na⁺/Na. Compression tests reveal that the nanoparticles in the oxychloride electrolytes improve the mechanical strength. Our findings will facilitate the development of solid electrolytes composed of nanoparticles balanced with high ionic conductivities, formabilities, and electrochemical stabilities.