The preparation and electrochemical study of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium-ion battery

To improve the cycling performance of nickel-rich layered LiNi_0.6Co_0.2Mn_0.2O₂ material, many methods have been studied to reduce cation mixing degree, improve layered structure and modify particle morphology, including doping elements, coating metal oxides and morphology control (spherical, nanoflower, core–shell structure, etc.). In this paper, a new gradient calcination process through four-step temperature gradients is applied to synthesize LiNi_0.6Co_0.2Mn_0.2O₂ material. The LiNi_0.6Co_0.2Mn_0.2O₂ material synthesized by gradient calcination shows more excellent electrochemical performance than traditional method. The XRD results indicate that the LiNi_0.6Co_0.2Mn_0.2O₂ material produced by four-step calcination shows lower cation mixing degree and better crystallinity. In addition, the LiNi_0.6Co_0.2Mn_0.2O₂ cathode produced by gradient calcination presents the highest initial capacity (177.9 mAh g⁻¹) and a retention of 82.07% after 100 cycles at 0.2C. And the material shows the best electrochemical properties when the final temperature in these steps is 820 °C. Our results explain the reason why the thermal stability and electrochemical performance could be improved by gradient calcination from the aspect of material crystallinity, crystal defects, cation mixing degree and the completeness of the layered structure.