Lithium calcium imide [Li2Ca(NH)2] for hydrogen storage: structural and thermodynamic properties

In an attempt to tailor the dehydrogenation temperature of lithium imides, we have investigated the ternary imide Li 2Ca(NH) 2, which crystallizes in a structure (space group P3 m1) different from that of Li 2Mg(NH) 2 (space group Iba2). First-principles density functional calculations yield the stable ground-state structure along with the correct hydrogen positions. Compared with the structural and thermodynamic data of the pure lithium imides, those Ca or Mg partially substituted ternary imides show decreased reaction enthalpies as well as dehydrogenation temperatures.