Closo-type complex hydride solid solutions for stabilizing the super-ionic phase

Abstract

Complex hydrides have garnered attention after the discovery of their lithium-ion conducting property, but they soon faced the limitation of low ionic conductivity at room temperature. In response, extensive research has been conducted to stabilize the high-T phase, which exhibits high ionic conductivity, at room temperature. Starting with research on LiBH4, recent studies discovered that the high-T phase of Li(CB9H10), one of the closo-type complex hydrides, can be successfully stabilized at room temperature by forming a solid solution with other closo-type complex hydrides. Building on this finding, in this study, efforts were made to stabilize the high-T phase of Li(CB11H12), which was not stabilized by forming a solid solution with Li(CB9H10) alone. Li2(B12H12) was additionally incorporated into the solid solution, and the resulting changes due to the coexistence of three closo-type complex anions were investigated. Consequently, the high-T phase of Li(CB11H12) was not stabilized at room temperature. As the amount of [B12H12]2⁻ anions increased, it deviated further from the disordered phase. Subsequently, Li1.125(CB11H12)0.55(CB9H10)0.325(B12H12)0.125, which exhibits superionic conductivity, was selected for battery testing. The battery, comprising a Li metal anode and a high- voltage oxide-based cathode, operated even at high C-rates.