Synthesis And Modification Study Of Lithium Ion Battery Li-rich Cathode Material Li_1.2Ni_0.2Co_0.08Mn_0.52O₂

Nowadays cathode materials have become a bottleneck for the development of lithium-ion batteries.Developing high performance cathode materials with high specific capacity and long cycle life is of great importance.Lithium-rich cathode materials have attracted wide attention due to their high theoretical specific capacity and high voltage platform.However,the drawbacks,such as poor cycle performance,relatively low specific capacity have hindered their commercial application in lithium ion batteries.In this paper,Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ cathode material was prepared by co-precipitation method,and then the material was modified by K⁺-doping and Al₂O₃-coating,respectively.XRD,SEM,TEM and XPS were performed to detect the microstructure,morphology and elements distribution of as-prepared materials.Galvanostatic charge-discharge,cyclic voltammetry,electrochemical impedance spectroscopy tests were also conducted to analyze the electrochemical properties of the materials.?1?The synthesis conditions of Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ cathode materials were investigated.We studied the effects of transition metal ion concentration,reaction time and calcining temperature on microstructure and electrochemical properties of as-prepared materials and found that the condition of 1.0 mol L^-1,15 h,900°C is appropriate.?2?K⁺-doped Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ material?denoted as LNCM-K?was synthesized by a simple co-precipitation method.XRD and SEM indicate that LNCM-K has well-ordered structure and better morphology.The LNCM-K shows an ultra-high specific capacity of 280.4 mAh g^-1 at 0.5 C rate and room temperature,with the capacity retention of 93.4%after 200 cycles.The excellent electrochemical properties can be attributed to the K⁺-doping,which enlarges the Li layers and provides more space for Li⁺,thus facilitates the intercalation/deintercalation of Li⁺.Meanwhile the K⁺-doping can inhibit the formation of spinel phase.The kinetics of lithium ion intercalation/deintercalation were also studied by electrochemical impedance spectroscopy.It was found that the charge transfer impedance decreases and the lithium ion diffusion coefficient increases as temperature increases.The activation energy of charge transfer and lithium ion diffusion are calculated to be 60and 120 kJ mol^-1,approximately.The activation energy of lithium ion diffusion is larger than that of charge transfer,implying the slow diffusion of lithium ions and relatively high electrochemical reaction.?3?Al₂O₃-coated Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ material was synthesized by solvothermal method.Al₂O₃ coating can improve the cycling stability at room temperature as well as elevated temperature.The capacity retention of Al₂O₃ coated sample is above 92%after 150 cycles at 0.5 C rate and room temperature,even at elevated temperature of 85°C,the capacity retention rate still exceeds 70%after cycling 200 cycles at 5 C rate,indicating outstanding cycling performance.