First-principle calculations of stable configurations and electronic structures of pristine and discharged spinel Mg1.31V1.67-xNixO4 (x = 0, 0.13) as cathode materials for magnesium secondary batteries

Abstract

The stable configurations and electronic structures of spinel Mg1.31V1.67-xNixO4 (x = 0, 0.13) in pristine and discharged samples were determined using first-principles calculations. Structural relaxation, transition state, and projected density of states calculations were performed using density functional theory. Structure relaxation of pristine and discharged Mg1.31V1.67-xNixO4 (x = 0, 0.13) demonstrated that Mg in the 8a site moved to a vacant 16c site during the discharge process. When the Mg insertion was equal to 0.5, the ratio of the structural change from spinel to rock-salt was approximately 0.5. NEB calculations indicated that the energy barrier for Mg diffusion from the 8a site to the 16c site of Mg1.31V1.57Ni0.1O4 was lower than that of Mg1.31V1.67O4. Electron density analysis was used to analyze the covalency between the metals and oxygen, confirming that the covalencies of the V-O and the Mg8asite-O bonds in Mg1.31V1.57Ni0.13O4 were respectively stronger and weaker than that of Mg1.31V1.67O4. Based on the overlap of the d-orbital of vanadium and the p-orbital of oxygen in Mg1.31V1.67-xNixO4 (x = 0, 0.13), the covalency of vanadium and oxygen was constructed from the projected density of states.