Experimental and theoretical studies of the LiBH-LiI phase diagram.

The hexagonal structure of LiBH at room temperature can be stabilised by substituting the BH anion with I, leading to high Li-ion conductive materials. A thermodynamic description of the pseudo-binary LiBH-LiI system is presented. The system has been explored investigating several compositions, synthetized by ball milling and subsequently annealed. X-ray diffraction and Differential Scanning Calorimetry have been exploited to determine structural and thermodynamic features of various samples. The monophasic zone of the hexagonal Li(BH)(I) solid solution has been experimentally defined equal to 0.18 ≤ ≤ 0.60 at 25 °C. In order to establish the formation of the hexagonal solid solution, the enthalpy of mixing was experimentally determined, converging to a value of 1800 ± 410 J mol. Additionally, the enthalpy of melting was acquired for samples that differ in molar fraction. By merging experimental results, literature data and theoretical calculations, the pseudo-binary LiBH-LiI phase diagram has been assessed and evaluated across all compositions and temperature ranges by applying the CALPHAD method.