High capacity and stability of Nb-doped Li3VO4 as an anode material for lithium ion batteries

Abstract

To improve the electrochemical performance of Li3VO4, a series of Li3NbxV1-xO4 compounds are prepared via sol-gel method. The similar ionic radii of Nb5+ and V5+ in octahedral coordination make it possible to form single-phased Li3NbxV1-xO4 (0 ≤ x ≤ 0.15). Theoretical calculations show that Li-ions migrate along the c-axis diffusion channel in a curved hopping route. The larger lattice constant caused by the substitution of V with Nb enhances the cross-sectional area, which indirectly provides a higher diffusion coefficient for Li-ion migration. Benefitting from high electronic conductivity (around two orders of magnitude) and good lithium-ion diffusion coefficient, the Li3NbxV1-xO4 (x = 0.02) exhibits the best electrochemical property as an anode of LIBs in comparison to other Li3NbxV1-xO4(x = 0, 0.01, 0.03, 0.04). At the current density of 30 mA g−1, the charge capacity of pure Li3VO4 is around 440 mA h g−1, whereas the Li3NbxV1-xO4 (x = 0.02) shows a higher capacity of 550 mA h g−1. Additionally, the charge/discharge capacities for Nb-doped samples are almost twice to those of the undoped Li3VO4 when the current density increases to1500 mA g−1.