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⋅CH3NH2 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. A fast solid‐state Li‐ion conductor based on methylamine lithium borohydride is reported. The new compound crystallizes in a layered two‐dimensional structure with fast Li‐ion migration in the interlayers. The first all‐solid‐state battery using a lithium borohydride with a neutral ligand as electrolyte is demonstrated with Li‐metal as the anode and TiS2 as the cathode material.