Incorporation of Ammonia Borane Groups in the Lithium Borohydride Structure Enables Ultrafast Lithium Ion Conductivity at Room Temperature for Solid-State Batteries

Conduction with fast Li ion conductivity at room temperature is a major challenge for the development of all solid-state Li-ion batteries. Herein, we demonstrate a novel room-temperature ultrafast Li-ion conductor, lithium borohydride ammonia borane complexes ((LiBH4)x·AB). The incorporation of AB into the LiBH4 structure intrinsically increases the cell volume and decreases the volume density of Li ion, which substantially facilitates the Li-ion conduction. The LiBH4·AB complex delivers up to 4.04 × 10–4 S cm–1 of ion conductivity at 25 °C with nearly negligible electron conductivity. The Li-ion transference number is higher than 0.999 at 40 °C. The room-temperature Li-ion conductivity obtained is largely superior to other LiBH4-based solid-state electrolytes reported previously under identical conditions. Moreover, the ultrafast Li-ion conduction remains stable upon heating and cooling cycling (18–55 °C). Ab initio molecular dynamics simulations display a kind of 1D Li diffusion channel along the b direction in the LiBH4·AB structure, which offers a much lower activation energy barrier (0.12 eV), consequently enabling superior Li-ion conductivity at room temperature.