Effect of the structural evolution on the ionic conductivity of Li-N-H system during the dehydrogenation

Abstract

On the way to transform lithium amide (LiNH2) into lithium imide (Li2NH) by releasing H2, the 1:1 molar mixture of LiNH2-LiH forms cubic (Fm3¯m) non-stoichiometric complex hydride phases (Li1+xNH2−x; 0 < x < 1) that co-exist with the tetragonal (I4¯) LiNH2 and with the cubic (Fd3¯m) Li2NH, respectively, at the early and at the advanced stage of the dehydrogenation. The change in LiNH2 → Li2NH may be viewed as a mechanism which continuously fills up the vacant Li sites of the tetragonal structure and, in a parallel process, transforms the anions [NH2]− → [NH]2−. The Li-N-H system, thus formed, by releasing >6 wt. % H2 can offer high Li-ionic conductivity (>10−4 S·cm−1 at room temperature) having an electrochemical stability window >5 V. The study suggests that the Li-N-H system may be a prospective electrolyte in the all-solid-state Li-ion battery, in addition to its use as a reversible hydrogen storage material.