Insights into the Lithium Sub-structure of Superionic Conductors Li ₃ YCl ₆ and Li ₃ YBr ₆

The recent interest in halide-based solid electrolytes Li3MX6 (M = Y, Er, and In; X = Cl, Br, and I) shows these materials to be promising candidates for solid-state battery application, due to their high ionic conductivity and large electrochemical stability window. However, almost nothing is known about the underlying lithium sub-structure within those compounds. Here, we investigate the lithium sub-structure of Li3YCl6 and Li3YBr6 using temperature-dependent neutron diffraction. We compare compounds prepared by classic solid-state syntheses with mechanochemical synthesis to shed light on the influence of the synthetic approach on the reported yttrium disorder and the resulting surrounding lithium sub-structure. This work provides a better understanding of the strong differences in ionic transport depending on the synthesis procedure of Li3MX6.