DFT study of Mg2TiO4 and Ni doped Mg1.5Ni0.5TiO4 as electrode material for Mg ion battery application

Mg 2 TiO 4 is a spinel material, however it is electrochemically inactive. We have simulated Ni doping in its tetrahedral network by partially replacing Mg +2 (0.5 Mg +2 ) ions with Ni +2 to form Mg 1.5 Ni 0.5 TiO 4 . Mg 2 TiO 4 , Mg 1.5 Ni 0.5 TiO 4 and its de-intercalated end product MgNi 0.5 TiO 4 are studied through analysis of structural parameters and density of states. All the three materials produce almost similar x-ray diffraction pattern ensuring structural stability during charge–discharge. After doping of Ni, Mg 1.5 Ni 0.5 TiO 4 becomes electrochemically active, as, only Ni states are found to be contributing charges (electrons) to the conduction band of MgNi 0.5 TiO 4 after de-intercalation. This redox activity is also supported from the magnetic moments of Ni indicating change in valance from +2 to +3 on de-intercalation. Calculation of de-intercalation voltage for de-intercalation of tetrahedral Mg from Mg 1.5 Ni 0.5 TiO 4 indicates a value of 4.22 V. This high voltage with electrochemical capacity 151 mAh g −1 would generate energy density of 637.2 W–h kg −1 . Simulation of formation energy (E f ) of Mg 1.5 Ni 0.5 TiO 4 indicates that with rutile TiO 2 the phase formation is probable with slightly negative value of formation energy, however, with anatase TiO 2 the phase formation is highly probable with high negative value of formation energy (E f ).