Synthesis And Modification Of Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ Cathode Material With High Performance For Lithium-ion Batteries

With the development of society,more strict performance of lithium-ion batteries is required,and it is increasingly difficult for traditional lithium-ion battery cathode materials to meet the market demand.The lithium-rich cathode material is considered to be one of the most promising cathode materials for next-generation lithium-ion batteries due to their high energy density,high specific capacity,and low cost.However,its commercial application is limited by several problems,such as large initial irreversible capacity,serious capacity and voltage decay and inferior rate capability.In this paper,Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ lithium-rich cathode materials were synthesized by two different methods of spray drying and co-precipitation,and they were modified by constructing appropriate concentration of oxygen vacancies and carbon coating,Cr₂O₃ coating,potassium ion doping and Cr₂O₃ coating,respectively.XRD,XPS,EPR and SEM are used to characterize the structure of the material.Its electrochemical performance and electrical properties are measured by charging and discharging testers and other instruments.The specific work is as follows:（1）The precursor is prepared by spray drying method.The synergistic modification of the appropriate amount of oxygen vacancy concentration and carbon coating is realized by adjusting the calcining gas atmosphere while the material is synthesized（the sample is denoted as CA@LNCM-2）.XRD characterization shows the existence of a lithium-rich phase and a complete layered structure of CA@LNCM-2;SEM and TEM have observed that the CA@LNCM-2 particles have an irregular cubic morphology and have carbon coating layer on surface.The EPR and XPS results show the oxygen vacancy concentration of the CA@LNCM-2 is between the other two control samples.The co-modified material has an initial coulombic efficiency of 83.1%at a current density of 0.1 C,and a capacity retention of 78.3%after 1,000cycles at 5 C,showing excellent electrochemical performance.（2）Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ was prepared by the co-precipitation method and was coated with Cr₂O₃ by the"wet chemical"method.The modified material shows better cycle stability than pristine materials at the current density both 1 C and 5 C.The capacity retention of the modified material are 85.29%after 200 cycles at 1 C（only 77.12%for pristine materials）and71.5%after 500 cycles at 5 C（only 28.6%for pristine materials）.And the influence of the Cr₂O₃ coating layer on the stability of the material structure was explored by XRD,SEM and other methods.（3）The potassium ion-doped Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ material（denoted as K-LNCM）was prepared by the co-precipitation method.Then K-LNCM was coated with Cr₂O₃ by the"wet chemical"method to obtain the co-modified material.The influence of potassium ion doping on kinetics of the material was explored by the AC impedance method.Electrochemical tests show that the cycle performance and rate performance of the co-modified material are better than that of the only coated-modified material:the capacity retention of the co-modified material is 80.6%after 500 cycles at 5 C,and the specific discharge capacity is 148.9 m Ah g^-1at high current density of 10 C.