  Because substitutions of BH4- anion with Br can stabilize the hexagonal
structure of the LiBH4 at room temperature, leading to a high Li-ion
conductivity, its thermodynamic stability has been investigated in this work.
The binary LiBH4-LiBr system has been explored by means of X-ray diffraction
and differential scanning calorimetry, combined with an assessment of
thermodynamic properties. The monophasic zone of the hexagonal Li(BH4)1-x(Br)x
solid solution has been defined from x=0.30 to x=0.55 at room temperature.
Solubility limits have been determined by in-situ X-ray diffraction at various
temperatures. For the formation of the h-Li(BH4)0.6(Br)0.4 solid solution, a
value of the enthalpy of mixing has been determined experimentally equal to 1.0
kJ/mol. In addition, the enthalpy of melting has been measured for various
compositions. Lattice stabilities of LiBH4 and LiBr have been determined by ab
initio calculations, using CRYSTAL and VASP codes. Combining results of
experiments and theoretical calculations, the LiBH4-LiBr phase diagram has been
determined in all composition and temperature range by the CALPHAD method.
