Theoretical and Experimental Studies of LiBH4-LiBr Phase Diagram

Because substitutions of BH4-anion with Br-can stabilize the hexagonal structure of the LiBH4at 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)xsolid solution has been defined equal to 0.30 ≤x≤ 0.55 at 30 °C. Solubility limits have been determined byin situX-ray diffraction at various temperatures. For the formation of theh-Li(BH4)0.6(Br)0.4solid solution, a value of the enthalpy of mixing (ΔHmix) has been determined experimentally equal to −1.0 ± 0.2 kJ/mol. In addition, the enthalpy of melting has been measured for various compositions. Lattice stabilities of LiBH4and LiBr have been determined byab initiocalculations 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 ranges by the CALPHAD method.