Stabilization of superionic-conducting high-temperature phase of Li(CB9H10) via solid solution formation with Li2(B12H12)

Abstract

We report the stabilization of the high-temperature (high-T) phase of lithium carba-closodecaborate, Li(CB9H10), via the formation of solid solutions in a Li(CB9H10)-Li2(B12H12) quasi-binary system. Li(CB9H10)-based solid solutions in which [CB9H10]- is replaced by [B12H12]2- were obtained at compositions with low x values in the (1-x)Li(CB9H10)-xLi2(B12H12) system. An increase in the extent of [B12H12]2- substitution promoted stabilization of the high-T phase of Li(CB9H10), resulting in an increase in the lithium-ion conductivity. Superionic conductivities of over 10-3 S cm-1 were achieved for the compounds with 0.2 ≤ x ≤ 0.4. In addition, a comparison of the Li(CB9H10)-Li2(B12H12) system and the Li(CB9H10)-Li(CB11H12) system suggests that the valence of the complex anions plays an important role in the ionic conduction. In battery tests, an all-solid-state Li-TiS2 cell employing 0.6Li(CB9H10)-0.4Li2(B12H12) (x = 0.4) as a solid electrolyte presented reversible battery reactions during repeated discharge-charge cycles. The current study offers an insight into strategies to develop complex hydride solid electrolytes.