Abstract: The effect of Ti doping on the hydrogen storage performance of Li₂MgN₂H₂ materials and its mechanism were investigated by the first-principles plane-wave pseudopotential method based on the density functional theory. The impurity replacement energy, formation enthalpy, energy band structure, density of states, differential charge density and population were calculated. The results show that when Ti atom is doped with Li₂MgN₂H₂ system, it tends to occupy the Mg lattice sites, and when replacing Mg at position 8c, the impurity replacement energy is the lowest and the crystal structure is the most stable. The calculation results of the formation enthalpy indicate that Ti doping can effectively reduce the structural stability of Li₂MgN₂H₂, which is beneficial to its hydrogen absorption reaction. Further combined with the analysis of the electronic structure, it is found that for the Li₂MgN₂H₂ materials after Ti doping, the unit cell volume increases and the energy gap reduces. At the same time, because of the strong interaction between Ti and N atoms, the peak value of the Li—N and N—H bonds reduces, and the bond strength weakens. These factors are all conducive to the improvement of the hydrogen absorption kinetic performance of the Li₂MgN₂H₂ material.

Key words: first-principle, Li-Mg-N-H, Ti doping, enthalpy of formation, electronic structure, hydrogen storage