Hemiammine lithium borohydride, LiBH₄·1/2NH₃, is characterized and a new Li⁺ conductivity mechanism is identified. It exhibits a Li⁺ conductivity of 7 × 10⁻⁴ S cm⁻¹ at 40 °C in the solid state and 3.0 × 10⁻² S cm⁻¹ at 55 °C after melting. The molten state of LiBH₄·1/2NH₃ has a high viscosity and can be mechanically stabilized in nano-composites with inert metal oxides and other hydrides making it a promising battery electrolyte.