Intermediate phases observed during decomposition of LiBH4

Lithium tetrahydridoboranate is among the materials with the highest hydrogen content and has great potential as a possible H2-storage material, although, the release and uptake of H2 is not fully understood. In this work, LiBH4 was studied by in situ synchrotron radiation powder X-ray diffraction (PXD) and solid state CP/MAS NMR both at variable temperatures. This study revealed two new phases observed during dehydrogenation of LiBH4. Phase I is hexagonal, a = 4.93(2) and c = 13.47(3) Å and is observed in the temperature range ∼200–300 °C, and phase II is orthorhombic, a = 8.70(1), b = 5.44(1) and c = 4.441(8) Å and is observed in the temperature range ∼300–400 °C applying a constant heating rate of 5 °C/min. Apparently, I transforms into II, e.g. at a constant temperature of T = 265 °C after 5 h. Furthermore, a third phase, III, is observed in the temperature range RT to 70 °C, and is caused by a reaction between LiBH4 and water vapor from the atmosphere. Hydrogen release is associated with the decomposition of III at ca. 65 °C.