Effect of heat-treatment on electrochemical performance of Li3VO4-coated LiNi1/3Co1/3Mn1/3O2 cathode materials

The surfaces of LiNi1/3Co1/3Mn1/3O2 particles were modified by Li3VO4 and the influences of heat-treatment were firstly studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). The results show that Li3VO4 is well crystallized and homogenously coated on the surfaces of LiNi1/3Co1/3Mn1/3O2 after heating by 700 °C for 8 h. Electrochemical tests demonstrate that the Li3VO4-coated sample heated at 700 °C exhibits excellent cycling performances with 87.5% capacity retention at 1 C after 100 cycles under high cut-off voltage of 4.6 V, meanwhile, the rate capability is also dramatically improved even under the high current densities, it delivers capacities as high as 144.2 and 137.5 mAh g−1 at 5 and 10 C respectively, which are much higher than that of pristine one and Li3VO4-coated samples heated at other temperatures. The electrochemical impedance spectroscopy (EIS) analysis reveals that Li3VO4 coating can diminish the charge transfer impedance which is caused by the continuously coating layer which could suppress side reactions between cathode material and electrolyte during the charge-discharge processes.