Superionic Conductivity Invoked by Enhanced Correlation Migration in Lithium Halides Solid Electrolytes

Lithium halides are experiencing reflorescence as a promising solid electrolyte in all-solid-state batteries (ASSBs) owing to their moderate conductivities and high oxidation potential. Herein we report new lithium-superionic chlorides, Li_3–xSc_1–xZr_xCl₆ and Li_3–xSc_1–xHf_xCl₆ (x = 0.25, 0.50, 0.625, 0.75), that demonstrate high ionic conductivities up to 2.2 mS cm^–1 at room temperature coupled with low activation energy barriers (0.31 and 0.33 eV for Zr and Hf-analogy, respectively). This notably improved conductivity upon Zr⁴⁺/Hf⁴⁺ substitution is ascribed to the decreased energy barrier along the c axis and enhanced correlated migration invoked by the tuned Li⁺/vacancy concentration. Evaluation in solid-state cells further confirmed the potential of this electrolyte to be used in high voltage ASSBs. Our work elucidates the impact of tuned cationic/vacancy concentration and consequently enhanced correlated migration on cationic conductivity. This strategy can be extended to other systems and serve as a guideline for the design of fast ion conductors.