Insights into the Lithium Substructure of the Superionic Conductors Li3YCl6 and Li3YBr6

The recent interest in the halide-based solid electrolytes Li₃MX₆ (M = Y, Er, In; X = Cl, Br, I) shows these materials to be promising candidates for solid-state battery application, due to 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 a 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.