Synergistic Effects of Mg and N Cosubstitution on Enhanced Dehydrogenation Properties of LiBH₄: A First-Principles Study

A metal + nonmetal (Mg + N) partial cosubstitution method for improving the dehydrogenation properties of lithium borohydride (LiBH₄), which is a potential solid hydrogen storage material, is proposed. A detailed analysis of the electronic structure, charge density redistribution, and dehydrogenation properties reveals that the cosubstitution has a more positive effect on several properties, including the thermal stability, hydrogen dissociation energy, and dehydrogenation temperature, than the single substitution of Mg or N. When Mg and N are codoped into LiBH₄, its formation enthalpy increases from −0.332 to −0.293 eV·atom–¹ and its thermal stability decreases. Moreover, density functional theory calculations of the Mg + N cosubstituted system show that its hydrogen dissociation energy is the lowest and the onset dehydrogenation temperature is reduced to 160.5 °C, indicating that Mg + N cosubstitution can significantly promote the dehydrogenation thermodynamic performance of LiBH₄ materials.