Full-gradient structured LiNi_0.8Co_0.1Mn_0.1O₂ cathode material with improved rate and cycle performance for lithium ion batteries

LiNi_0.8Co_0.1Mn_0.1O₂ cathode material with full-gradient structure is prepared by a novel co-precipitation method. Scanning electron microscope images show that the material presents regular spherical shape. X-ray diffraction pattern shows that the material has good layered structure. Energy dispersive X-ray spectroscopy analysis for the cross section of secondary particles shows that the relative molar content of Ni gradually decreases from 84% to 76% along the center to the edge of hemisphere, while the Mn content increases gradually. Moreover, the Co content also presents a slow gradient change. Electrochemical tests at room temperature show that the retention rates of discharge capacity for full-gradient material after 100 cycles at current density of 1C and 5C are 98.8% and 93.7%, respectively, which are obviously improved compared with intrinsic material. The gradient material also shows improved midpoint voltage and specific energy. Moreover, full-gradient material exhibits good cyclic stability at high temperature, and the capacity retention rate of 100 cycles is as high as 90% at 5C rate, which is obviously higher than 71.8% of intrinsic material. Impedance spectroscopy studies show that the solid-state diffusion coefficient of lithium ion in gradient material has been significantly improved, thus showing good electrochemical properties. The full-gradient material shows excellent application prospects in the field of power batteries.