Lithium ion conduction in lithium borohydrides under high pressure

The high-pressure effects on lithium ion conduction in LiBH4 have been investigated. The high-pressure ac-impedance measurement was performed by using a cubic anvil-type apparatus under 2 to 6 GPa at various temperatures. For the hexagonal structure (Phase I), the activation volume for lithium ion conduction was found to be around 3 cm3/mol (≈ 0.09Vm, where Vm means its molar volume). This activation volume is almost comparable to that for other fast-ion conductors such as NASICONs. The lithium ion conductivities of orthorhombic (Phase III) and cubic (Phase V) structures were also measured. Regardless of crystal structures, the activation energies of Phases I, III, and V were almost identical at around 50 to 60 kJ/mol; on the other hand, the pre-exponential terms of Phases III and V were smaller than those of Phase I by one to two orders of magnitude.