Improvement of the thermodynamic properties of lithium borohydride LiBH4 by mechanical treatment for hydrogen storage applications: A DFT investigation

Abstract

In the present work, single, double and triaxial (tensile/compression) strains were applied to lithium borohydride LiBH4 using Density Functional Theory (DFT) based on Perdew-Burke-Ernzerhor for solids (PBEsol) approach. The results show that the structural properties change with the deformation amplitude. The total density of state (TDOS) and partial density of state (PDOS) studies show that the LiBH4 complex hydride is an insulator with an energy band gap of 6.73 eV and the width of the valence and conduction bands vary with the change of the strain amplitude. The deformation energy shows that triaxial deformation on LiBH4 complex hydride requires more energy than single and double strains. Hence, these deformations are found responsible for the decrease of the thermodynamic properties of LiBH4 hydride. Specifically, under a maximum uni/bi/triaxial compressive strain of ε = −9%, the enthalpy of formation and decomposition temperature decrease by 3.25 %, 7.59 %, and 36.54 %, respectively. While, under a maximum uni/bi/triaxial tensile strain of ε = +9 %, the enthalpy of formation and decomposition temperature decrease by 3.85 %, 11.83 %, and 26.44 %, respectively, compared to unstrained hydride. Consequently, the findings are in excellent agreement with the standards of the U.S. Department of Energy (DOE) (ΔHf = −40 Kj/mol.H2 and Td = 289–393 K) for hydrogen storage in the solid state.