First-principles study of a double-cation alkali metal borohydride LiK(BH4)2

Metal borohydrides have been attracting great interest as potential candidates for use as advanced hydrogen storage materials because of their high gravimetric hydrogen densities. In the present study, first-principles calculations have been performed for the newly reported dual-cation alkali metal borohydride LiK(BH(4))(2), using density functional theory (DFT) within the generalized gradient approximation and the projected augmented wave method. LiK(BH(4))(2) is found to have an orthorhombic structure in the space group Pnma (No 62) with nearly ideal tetrahedral shape. It is an insulating material having a DFT-calculated wide band gap of 6.08 eV. Analysis of the electronic structure shows an ionic interaction between metal cations and (BH(4))(-) and the covalent B-H interaction within the (BH(4))(-) tetrahedron. The enthalpy of the formation reaction from primary elements is calculated and found to be -449.8 kJ mol(-1). The decomposition temperature (T(dec)) of LiK(BH(4))(2) lies between those of LiBH(4) and KBH(4), which suggests that the hydrogen decomposition temperature of metal borohydrides can be precisely adjusted by the appropriate combination of cations.