Density function theory investigation on the thermodynamic properties of the Li–N–H system

• The structures and enthalpies of compounds in the Li–N–H system are investigated.
• The chemical potential phase diagrams of compounds are computed.
• Changing the hydrogen chemical potential, six reversible reactions are discussed.
• Evaluating the competition between each reaction in the Li–N–H system.

The electronic structures and formation enthalpies of compounds in the Li–N–H system have been studied by using the density functional theory. In order to evaluate the competition between each reaction in the system, the chemical potential phase diagrams of compounds in the Li–N–H system have been computed and discussed. Our calculations show that for LiNH2, Li+ combines with [NH2]- by an ionic bond. For Li2NH, the N–H bond displays covalent characteristics. The calculated formation enthalpy of compounds in the Li–N–H system is in agreement with previous results, the LiNH2 is −212.27 kJ mol−1, LiH is −91.66 kJ mol−1, Li2NH is −243.14 kJ mol−1, Li4NH is −309.72 kJ mol−1, Li3N is −189.11 kJ mol−1, and NH3 is −102.27 kJ mol−1, respectively. Using the chemical potential phase diagrams, six reversible reactions are discussed. It is found that Li4NH takes part in the three reversible reactions and some NH3 formed in the system react with other compounds in the Li–N–H system. These reversible reactions are confirmed by the proposed mechanism from experiments.