Methylamine Lithium Borohydride as Electrolyte for All‐Solid‐State Batteries

Abstract 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. LiBH 4 ⋅CH 3 NH 2 crystallizes in the monoclinic space group P 2 1 / c , forming a two‐dimensional unique layered structure. The layers are separated by hydrophobic −CH 3 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 TiS 2 as the cathode is demonstrated.