Theoretical study of Li-ion migration in perovskite­type AVO3 (A = Ca, La, Ce, and La0.75Ca0.25) with DFT+U methods

Abstract

Density functional theory (DFT) simulations were carried out to investigate the Li­-ion migration characteristics in perovskite-type vanadium oxides AVO3 (A = Ca, La, Ce, and La0.75Ca0.25). The formation energies of interstitial Li ions in the bulk phase of AVO3 were calculated by DFT+U, followed by the comparative analysis of the electronic structures of pure AVO3 and AVO3 containing the interstitial Li-ion, and finally the Li­ion migration paths and energy barrier values in AVO3 were determined using the NEB method of the interstitial Li-ion migration mechanism. The results showed that 8d site and 4c site are occupied by the Li ions in the AVO3. For the average lithiation voltage, values of CaVO3 and La0.75Ca0.25VO3 were larger than the corresponding values for LaVO3 and CeVO3. LaVO3 with the interstitial Li(8d) ion displayed a minimal rate of change in cell volume. The DOS calculations showed that AVO3 with the interstitial Li ion had better electrical conductivity than pure AVO3, and the conductivity of La0.75Ca0.25VO3 was enhanced compared to LaVO3. There were two migration paths in this system, where the minimum migration energy barriers for Li ions in CaVO3, LaVO3, CeVO3, and La0.75Ca0.25VO3 were 0.930 eV, 1.917 eV, 1.787 eV, and 1.756 eV respectively.