Methylamine Lithium Borohydride as Electrolyte for All-Solid-State Batteries.

Fast Li-ion conductivity at room temperature is a major challenge for utilization of all-solid-state Li batteries. Metal borohydrides with neutral ligands are a new emerging class of solid-state ionic conductors, and here we report the discovery of a new mono-methylamine lithium borohydride with very fast Li+ conductivity at room temperature. LiBH4 ⋅CH3 NH2 crystallizes in the monoclinic space group P21 /c, forming a two-dimensional unique layered structure. The layers are separated by hydrophobic -CH3 moieties, and contain large voids, allowing for fast Li-ionic conduction in the interlayers, σ(Li+ )=1.24×10-3  S cm-1 at room temperature. The electronic conductivity is negligible, and the electrochemical stability is ≈2.1 V vs Li. The first all-solid-state battery using a lithium borohydride with a neutral ligand as the electrolyte, Li-metal as the anode and TiS2 as the cathode is demonstrated.

Molten metal closo-borate solvates.

Solvated lithium closo-dodecaborate, Li2B12H12 with tetrahydrofuran and acetonitrile, show unexpected melting below 150 °C. This feature has been explored to melt-infiltrate Li2B12H12 in a nanoporous SiO2 scaffold. The ionic conductivity of Li2B12H12·xACN reaches 0.08 mS cm-1 in the liquid state at 150 °C making them suitable as battery electrolytes.