Preparation of Li-Excess and Li-Deficient Antiperovskite Structured Li2+xOH1-xBr and Their Effects on Total Ionic Conductivity.

Abstract

This paper describes about the effect of Li-H exchange amount on total lithium-ion (Li+) conductivity of Li2+xOH1-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 Li2+xOH1-xBr samples are formed within x = -0.5 to +0.35. For improving total Li+ conductivity (σt), 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 σt of 3.6 × 10-6 S cm-1 at the Li-excess Li2.2OH0.8Br composition, which is ca. 3 times higher than pristine Li2OHBr (1.1 × 10-6 S 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.