Enhancement of the lithium-ion conductivity of LiBH4 by hydration

Lithium borohydride (LiBH4) is a candidate material for a solid electrolyte of all-solid-state lithium secondary batteries. In this study, the hydration behavior and influences of hydration on the ionic conductivity of LiBH4 were investigated. LiBH4 was found to become hydrated without decomposing; structural water can dehydrate at 55 °C and then rehydrate at around 35 °C. Hydrated LiBH4 has a high lithium-ion conductivity of 4.89 × 10− 4 S ⋅ cm− 1 at 45 °C. The temperature dependence of conductivity and motional narrowing of the 7Li NMR spectra at around dehydration temperature suggest that the enhanced lithium-ion conductivity is attributed to the motion of structural water molecules.