Toward Achieving a High Ionic Conducting Halide Solid Electrolyte through Low-Cost Metal (Zr and Fe) and F Substitution and Their Admirable Performance in All-Solid-State Batteries

Recently, the halide solid electrolyte (SE) system has been widely used in lithium solid-state batteries due to their specific properties, such as the high electrochemical stability window that prevents any side reaction with the electrode/electrolyte interface. Conspicuously, the halide SE possesses very low ionic conductivity values in the range (0.2–0.5) mS cm –1 . In this work, we enhance the ionic conductivity of Li 3 YCl 6 SE by the substitution of low-cost Fe and Zr elements on the Y-site and F on the Cl site, in which the electrolyte is prepared through high-energy ball milling without a heat treatment process. The structural analysis reveals that the prepared halide SEs showed the pure phase of the Li 3 YCl 6 tetragonal crystal structure and were free from impurity phases. In the prepared composition, the Li 2.4 Y 0.4 Zr 0.6 Cl 6 and Li 2.4 Y 0.4 Zr 0.6 Cl 5.85 F 0.15 electrolyte exhibited a higher ionic conductivity of 2.05 and 1.45 mS cm –1, respectively, than Li 3 YCl 6 (0.26 mS cm –1 ). Interestingly, the Li 2.4 Y 0.4 Zr 0.6 Cl 5.85 F 0.15 electrolyte possesses a better electrochemical stability window of 1.29–3.9 V than Li 2.4 Y 0.4 Zr 0.6 Cl 6 (2.1–3.79 V). Moreover, the electrochemical results revealed that the assembled solid-state battery using Li 2.4 Y 0.4 Zr 0.6 Cl 6 and Li 2.4 Y 0.4 Zr 0.6 Cl 5.85 F 0.15 electrolyte demonstrated the higher initial Coulombic efficiency of 84.7 and 87%, respectively, than Li 3 YCl 6 of 82.6%. We consider Li 2.4 Y 0.4 Zr 0.6 Cl 5.85 F 0.15 to be an important electrolyte candidate in all-solid-state batteries.