DFT study of Li2NiTiO4 and vanadium-doped Li2NiTiO4

Density functional theory study of Li 2 NiTiO 4 and vanadium-doped Li 2 NiTiO 4 are performed for understanding their structural and electrochemical phenomena, viz., structural geometry like lattice parameters, change in lattice volume with Li + extraction, Li + de-intercalation voltage, electrochemical capacity etc. Li 2 NiTiO 4 has cubic symmetry with space group Fm3m (space group number 225). De-intercalated structure of LiNiTiO 4 is obtained by removing one Li atom from Li 2 NiTiO 4 unit cell while shifting another Li atom from octahedral site 4b to tetrahedral lattice site 8c. Due to Li + extraction, the change in unit cell volume is ~ 5.9%. Li + de-intercalation voltage is calculated by subtracting total energy of the unit cell of LiNiTiO 4 and bcc Li from Li 2 NiTiO 4 . The voltage comes out to be 4.84 V which is nearly at the threshold for electrochemical stability of used electrolytes. The redox couples in this case are Ni +2 /Ni 2 + δ and O −2 /O −2+γ . The presence of redox couple O −2 /O −2+γ leads to the probability of evolution of oxygen during charging. However, partial (50% in this case) vanadium doping at Ti site reduces the redox voltage to 4.64 V considering the de-intercalation reaction forming LiNiTi 0.5 V 0.5 O 4 from Li 2 NiTi 0.5 V 0.5 O 4 , by activating the redox couple V +3 /V +4 in Li 2 NiTi 0.5 V 0.5 O 4 . This also reduces the possibility of evolution of oxygen during de-intercalation reaction by shifting the main redox couple from O −2 /O −2+γ to V +3 /V +4 , which leads to greater structural stability of electrode materials during charge-discharge cycles.