Improving the Stability of Li₃HoBr₆ on Metallic Lithium by Using a Double-Halogen Strategy

Halide solid-state electrolytes have attracted much attention due to their high ionic conductivity, good deformability, and chemical stability with cathode materials, but their instability with lithium metal has seriously hindered further development in all-solid-state batteries. In this study, the Li 3 HoBr 6 electrolyte was doped with Cl – with high electronegativity to further improve the interface stability between the electrolyte and lithium metal, while maintaining the original monoclinic structure of Li 3 HoBr 6 and the ionic conductivity of the electrolyte (1.71 × 10 –3 S cm –1 ) without sacrificing the ionic conductivity of the electrolyte. The assembled Li/Li 3 HoBr 3 Cl 3 /Li symmetric cell (0.1 mA cm –2 ) was stably cycled for more than 800 h in a small overpotential state (0.26 V). Further research has shown that halide solid electrolytes are always unstable for metallic lithium, but Cl – -substituted Li 3 HoBr 3 Cl 3 electrolytes can effectively inhibit the generation of lithium bromide at the interface between halides and metallic lithium, which can improve the interface stability. The study demonstrates that changing the electronegativity of the halogenated elements in the electrolyte lattice will have a profound effect on ion transport in the bulk phase and on the intrinsic redox properties of the electrolyte.