The impact of vanadium substitution on the structure and electrochemical performance of LiNi0.5Co0.2Mn0.3O2

The influence of the vanadium substituted LiNi0.5Co0.2Mn0.3O2 (LNCM-532) cathode materials on the structure and electrochemical properties were investigated by means of X-ray diffraction, Rietveld refinement, scanning electron microscope, X-ray photoelectric spectroscopy, energy dispersive spectrometer, electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge/discharge tests. XRD, EDS, XPS results show that vanadium is successfully substituted for the transitional metal in LiNi0.5Co0.2Mn0.3O2 crystal lattice. Rietveld refinement results show that suitable vanadium substitution leads to low cation mixing. Electrochemical tests show that the discharge capacity of Li[Ni0.5Co0.2Mn0.3]0.97V0.03O2 at 5 C remains 72.2% of that at 0.1 C, while the capacity retention is only 58.9% for LiNi0.5Co0.2Mn0.3O2. LiNi0.5Co0.2Mn0.3O2 exhibits the capacity retention of 93.9% at 1 C after 50 cycles. After substituting, the capacity retention of Li[Ni0.5Co0.2Mn0.3]0.97V0.03O2 is increased to 96.3% at 1 C. EIS measurement indicates that vanadium substitution contributes to the better lithium ion diffusion and the lower charge transfer resistance.