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

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.