Room temperature lithium fast-ion conduction and phase relationship of LiI stabilized LiBH₄

In the present work, we focus attention on the effect of LiI addition to newly discovered pure lithium ion conductor, LiBH₄. Solid solution of the composition LiBH₄-LiI (LiI: 6.25-33.3 mol%) was synthesized by solid state reaction. Electrical conductivity was measured from room temperature to 140 °C by ac impedance method, which revealed the fast-ion conduction phase of LiBH₄ can be stabilized to lower temperature, below the room temperature. Solid solution with LiI showed higher conductivities and lower activation energies in comparison with LiBH₄. Powder XRD measurement was carried out at 120 °C (just above the transition temperature of LiBH₄). The lattice constants of the solid solution were determined. DSC measurement showed a systematic compositional dependence on the transition temperature. The stabilization mechanism was discussed.