Improved cycle stability and high-rate capability of Li_3VO_4-coated Li [Ni_(0.5)Co_(0.2)Mn_(0.3)]O_2 cathode material under different voltages

摘要

Li_3VO_4-coated Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O_2 cathode material exhibits much better cycling stability, rate capability, and high voltage cycling behavior than pristine Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O_2 at room temperature. The sample coated with 3 wt.% Li_3VO_4 shows the optimum electrochemical performance. It delivers a capacity of 61.5 mAh g~(-1) at 10 C (1800 mA g~(-1)) after 100 cycles. The capacity retention at 1 C (180 mA g~(-1)) is 63.5% at cut-off voltage 4.6 V, and 63.0% at a higher cut-off voltage 4.8 V. XRD and XPS results reveal that the Li_3VO_4 coating layer reinforces the surface of matrix material, which benefits structural stability of Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O_2 during long-term cycling. CV and EIS tests indicate that the improvement of electrochemical performances could be attributed to higher Li~+ conductivity, suppression of Co and Mn dissolution from Li[Ni_(0.5)Co_(0.2)Mn_(0.3)]O_2, and decreased polarization during cycling since Li_3VO_4 layer on Li [Ni_(0.5)Co_(0.2)Mn_(0.3)]O_2 surface acts as a relatively stable protective barrier as well as an excellent Li-ion conductor.