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. In this work, we enhance the ionic conductivity of LiYCl 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 LiYCl tetragonal crystal structure and were free from impurity phases. In the prepared composition, the LiYZrCl and LiYZrClF electrolyte exhibited a higher ionic conductivity of 2.05 and 1.45 mS cm, respectively, than LiYCl (0.26 mS cm). Interestingly, the LiYZrClF electrolyte possesses a better electrochemical stability window of 1.29-3.9 V than LiYZrCl (2.1-3.79 V). Moreover, the electrochemical results revealed that the assembled solid-state battery using LiYZrCl and LiYZrClF electrolyte demonstrated the higher initial Coulombic efficiency of 84.7 and 87%, respectively, than LiYCl of 82.6%. We consider LiYZrClF to be an important electrolyte candidate in all-solid-state batteries.