Exploring the structural, physical properties and hydrogen storage properties of LiBHx(x=1 and 4) lithium borohydrides

Abstract

To explore the correlation between the hydrogen concentration and electronic properties of the lithium borohydrides (LiBHx), we apply the first-principles method to study the influence of hydrogen (H) concentration on the structural stability, physical properties and hydrogen storage properties of LiBHx(x = 1 and 4). Two hydrogen concentrations are considered. The calculated results show that three LiBHx phases are thermodynamic stability because of the negative formation enthalpy. LiBH with the low concentration of hydrogen has better thermodynamic stability in comparison to LiBH4. In particular, the calculated gravimetric hydrogen storage capacity is 5.06 wt% for LiBH and 15.53 wt% for LiBH4, respectively. Essentially, the higher hydrogen storage capacity of LiBH4 is related to the product of [BH4] group because of the strong electronic interaction between B atom and H atom. Based on the m-GGA function, it is found that the calculated band gap is 0.044 for LiBH, 7.744 eV for the hexagonal LiBH4 and 7.908 eV for the orthorhombic LiBH4, respectively. Naturally, the calculated electronic structure shows that the wide band gap is related to the band separation between H-s state, Li-state and B-2p state near the Fermi level.