Ruddlesden-Popper phases of lithium-hydroxide-halide antiperovskites: two dimensional Li-ion conductors

Lithium-oxide-halide and lithium-hydroxide-halide antiperovskites were explored for potential electrolytes in all-solid Li-ion batteries. A single-phase sample of the Ruddlesden-Popper (RP) series of compounds, LiBr(Li₂OHBr)₂ with double antiperovskite Li₂OHBr layers and rigid rock-salt type LiBr layers, was obtained. Li⁺-ion vacancies are introduced in the double antiperovskite Li₂OHBr layers but not in the LiBr layers and induce two-dimensional Li-ion conduction with low activation energy by mediating Li-ion hopping. In contrast to the Br-containing RP phase, Cl-containing Li-oxide-halide and Li-hydroxide-halide RP phases cannot be crystallized due to the structural mismatch between the antiperovskite layers and rigid LiCl layers.