Experimental and Theoretical Analysis of Fast Lithium Ionic Conduction in a LiBH₄–C₆₀ Nanocomposite

We have developed a LiBH₄–C₆₀ nanocomposite that displays fast lithium ionic conduction in the solid state. The material is a homogeneous nanocomposite that contains both LiBH₄ and a hydrogenated fullerene species. In the presence of C₆₀, the lithium ion mobility of LiBH₄ is significantly enhanced in the as-prepared state when compared to pure LiBH₄. We also observed that after the material is annealed, the lithium ion mobility is further enhanced. The magnitude of enhancement in lithium ion mobility of the annealed material is comparable to that previously observed for LiX (X = halide) addition to LiBH₄. In a LiBH₄:C₆₀ 70:30 wt % sample that was annealed, we measured Li ionic conductivity of 2.0 × 10^–5 S/cm at 25 °C and 2.0 × 10^–3 S/cm at 140 °C. Constant current cycling demonstrated that the material is stable in the presence of metallic lithium electrodes. First-principles calculations were also performed to demonstrate how C₆₀ perturbs the interaction of lithium with the borohydride anion yielding a plausible explanation for the observed high ionic conductivity. The feasibility of this material as a solid state electrolyte was then demonstrated in a solid-state lithium ion battery