Bromide substitution in lithium borohydride, LiBH4―LiBr

By means of in situ synchrotron radiation powder X-ray diffraction, powder neutron diffraction, attenuated total reflectance infrared spectroscopy, differential scanning calorimetry and the Sieverts techniques we have investigated how anion substitution in the LiBH4--LiBr system leads to changes in the structural, physical, chemical and hydrogen storage properties of this material. Mechano-chemical treatment facilitates formation of a hexagonal solid solution h-Li(BH4)1-xBrx whereas heating at elevated temperatures, i.e. T > 112 ?C appears to allow full solubility in the system LiBH4-LiBr. The first step in the anion substitution process may be dissolution of small amounts of LiBH4 in Delta *a-LiBr deduced from observation of a hexagonal solid solution with unit cell volume similar to Delta *b-LiBr for a hand-mixed sample. The solid solution, Li(BH4)1-xBrx, is isostructural to the hexagonal high temperature polymorph of LiBH4. This solid solution melts at a significantly higher temperature depending on the composition as compared to h-LiBH4. Furthermore, a new hexalithium borate tribromide, Li6(BO3)Br3 was discovered and structurally characterized.