Thermodynamic functions and pressure-temperature phase diagram of lithium alanates by ab initio calculations

We report on a study of thermodynamic functions and phase stability of lithium alanates LiAl H4 and Li3 Al H6 using ab initio density-functional and quasiharmonic phonon calculations. The calculated thermodynamic functions are in good agreement with available experimental data and are used to study the decomposition reactions of these materials. The results show that the decomposition of LiAl H4 is irreversible under all temperature and pressure conditions considered, indicating that a direct synthesis of LiAl H4 from the solid reaction of (1 3 Li3 Al H6 + 2 3 Al+ H2) is not possible. Meanwhile, the calculated results suggest that Li3 Al H6 can be used as a rechargeable hydrogen-storage medium under certain temperature and pressure conditions. We construct the temperature-pressure phase diagram and present a discussion in conjunction with an analysis of recent experimental results.