Rotational disorder in lithium borohydride
1 Hydrogen and Energy, Empa, Swiss Federal Laboratories for Materials Science and Research, Dübendorf, Switzerland
2 Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen, Switzerland
3 ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK
4 Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, The Netherlands
5 Institute of Nuclear Physics, Polish Academy of Sciences, Kraków, Poland
6 École Polytechnique Fédérale de Lausanne (EPFL), Institut des Sciences et Ingénierie Chimique, Lausanne, Switzerland
a Corresponding author: firstname.lastname@example.org
Published online: 23 January 2015
LiBH4 has been discussed as a promising hydrogen storage material and as a solid-state electrolyte in lithium-ion batteries. It contains 18.5 wt% hydrogen and undergoes a structural phase transition at 381 K which is associated with a large increase in rotational disorder of the [BH4]− anion and the increase of [Li]+ conductivity by three orders of magnitude. We investigated the [BH4]− anion dynamic in bulk LiBH4, in LiBH4-LiI solid solutions and in nano-confined LiBH4 by quasielastic neutron scattering, complemented by DFT calculations. In all cases the H-dynamics is dominated by thermally activated rotational jumps of the [BH4]− anion in the terahertz range. The addition of LiI as well as nano-confinement favours the disordered high temperature phase and lowers the phase transition below room temperatures. The results are discussed on the basis of first principles calculations and in relation to ionic conductivity of [Li]+.
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