Interplay between Li3YX6 (X = Cl or Br) solid electrolytes and the Li metal anode

The interplay between solid electrolytes and electrodes is of vital importance to the performance of all-solid-state Li batteries. Recently, halide superionic conductors have emerged as a new family of high-performance solid electrolytes, but their compatibility with Li metal, i.e., the anode with the highest theoretical capacity, has not been systematically studied. Here, we investigate the interaction between Li metal and two representative halide solid electrolytes: Li3YCl6 and Li3YBr6. Both materials are found to form interphases with Li, similar to most solid electrolytes. However, the interphases observed here contain electronic conducting components, which are detrimental to their compatibility with Li. By elucidating this phenomenon, the present study provides guiding principles for improving the Li compatibility of halide solid electrolytes.