Preparation of Li-Excess and Li-Deficient Antiperovskite Structured Li_{2+ x}OH_{1- x}Br and Their Effects on Total Ionic Conductivity

This paper describes about the effect of Li-H exchange amount on total lithium-ion (Li⁺) conductivity of Li_2+xOH_1-xBr (x = -0.5 to +0.4). These samples are systematically prepared at room temperature by a dry ball-milling process using LiOH, LiOH·H₂O, Li₂O, and LiBr as starting materials. Synchrotron X-ray diffraction analysis reveals that single-phase Li_2+xOH_1-xBr samples are formed within x = -0.5 to +0.35. For improving total Li⁺conductivity (σ_t), a larger x value increases both the Li carrier density and lattice constant as positive factors, while that decreases both the crystallite size and OH rotational unit possibly assisting Li⁺conduction as negative factors. This trade-off provides an optimized σ_tof 3.6 × 10^-6S cm^-1at the Li-excess Li_2.2OH_0.8Br composition, which is ca. 3 times higher than pristine Li₂OHBr (1.1 × 10^-6S cm^-1). The hydrogen incorporation into the lattice is confirmed by neutron diffraction analysis, and the refined composition is almost consistent with the prepared composition.