Aliovalent Anion Incorporation in Halide Na-ion Conductors for Enhanced Ionic Conductivity

Halide-based solid electrolytes (SEs), particularly zirconium (Zr)-centered halides, are attractive from a material cost perspective. Nevertheless, Zr-centered halide SEs are hindered by their low ionic conductivity. Here, we report on the cubic Na3ZrCl5S superionic conductor through strategic sulfur anion incorporation, achieving 10 times higher ionic conductivity than that of Na2ZrCl6. With the optimal composition, the highest ionic conductivity of 0.753 mS cm–1 is obtained for the 0.6Na2S–1.4NaCl–ZrCl4 compound. When paired with a NaCrO2 cathode, the assembled all-solid-state batteries (ASSBs) achieve a specific discharge capacity of 110 mA h g–1 at 0.1C and exhibit long-term cycling stability at 0.3C at room temperature over 1000 cycles (with 83% capacity retention). Moreover, in situ electrochemical impedance spectroscopy combined with distribution of relaxation times analysis reveal the dynamically interfacial stability between Na halide with electrodes. This work highlights the design and synthesis of advanced halide electrolytes through anion incorporation, paving the way for the development of next-generation ASSBs.