Abstract:Li₃Mg_2xV_2-2x(PO₄)₃/C (x=0, 0.05, 0.1, 0.2) composites were synthesized by carbothermic reduction, using a self-made MgNH₄PO₄/MgHPO₄ compound as Mg-doping agent. X-ray diffraction (XRD), scanning electron microscope (SEM), electrochemical performance tests were employed to investigate the effect of Mg doping on Li₃V₂(PO₄)₃/C samples. The results showed that a proper quantity of Mg doping was beneficial to the reduction of charge transfer resistance of Li₃V₂(PO₄)₃/C compound without changing the lattice structure, which led to larger charge/discharge capacity and better cycle performance especially at high current density. Li₃Mg_2xV_2-2x(PO₄)₃/C sample with x=0.05 exhibited a better performance with initial charge/discharge capacity of 146/128 mA·h/g and discharge capacity of 115 mA·h/g at 5C, while these two figures were 142/118 mA·h/g and 90 mA·h/g respectively for samples without Mg doping, indicating that a proper amount of doped Mg can improve the electrochemical performance of LVP sample. All of these proved that, as a trial Mg dopant, the synthesized MgNH₄PO₄/MgHPO₄ compound exhibited well doping effect.

Key words: lithium vanadium phosphate; Mg-doping; cathode materials; carbothermic reduction