First-principles study of the paths of the decomposition reaction of LiBH4

A clear description of the paths of thermal decomposition of complex borohydrides represents a crucial step forward to their utilisation as a reservoir of hydrogen and hence as materials for solid state hydrogen storage. We present in this work a theoretical study of the possible paths of decomposition of LiBH4 by means of density functional theory approach. Our first-principles calculations showed the possibility to form linear chains of tetraborate of lithium in the residue of decomposition, among other thermodynamically competitive reactions. Their analytical formula LiBHx agreed with the quantitative analysis already reported by Schlesinger and co-workers in the 1940s. The structure showed the formula unit Li4B4H10, and the analytical formula LiBH2.5, of which the Gibbs free energy of formation was -111.76 kJ mol(-1). The lattice stability was confirmed by the phonon calculations, which revealed all positive normal modes. Comparatively, the formation of lithium dodecaborate(12) is presented and discussed. The calculated standard Gibbs free energy of the decomposition reactions considered in the present work were in the range (158,286) kJ mol(-1) of LiBH4 decomposed.