Synthesis And Modification Study Of Lithium Ion Battery Ni-rich Cathode Marterial LiNi_0.6Co_0.2Mn_0.2O₂

The cathode material is the key component of the lithium-ion battery.It determines the production cost and energy density of the battery.Therefore,it is necessary to develop a cathode material with good electrochemical performance（large specific capacity,high operating voltage）,cheap price and environmental friendliness.Ni-rich cathode materials meets the above conditions,but its long cycle performance and rate performance at high cut-off voltage are not ideal,which limits its application.In order to improve these deficiencies,Ni-rich cathode materials need to be modified by methods including ion doping and surface coating.In this paper,Ni-rich cathode materials Li Ni_0.6Co_0.2Mn_0.2O₂is prepared by the carbonate co-precipitation method,and it is modified by La,F co-doping and Li₂Mn O₃ coating,respectively.The structure of the modified material was characterized by XRD,SEM,TEM,XPS,etc.At the same time,the electrochemical performance of the modified material was analyzed by constant current charge and discharge test,cyclic voltammetry test,AC impedance test,etc.The specific research work is as follows:（1）The synthesis conditions of Ni-rich cathode materials Li Ni_0.6Co_0.2Mn_0.2O₂ were explored,and the effects of reaction time,transition metal ion concentration,and calcination temperature on the structure and electrochemical performance of the material were studied.By comparison,more suitable synthesis conditions were obtained:1.0 mol L^-1 metal ion concentration,12 h reaction time,and 850°C calcination temperature.The material synthesized under this condition has the best layered structure and electrochemical performance.（2）The La and F co-doped Ni-rich cathode material Li Ni_0.59Co_0.2Mn_0.2La_0.01O_1.98F_0.02 was successfully synthesized by a simple method.Compared with pristine sample,the modified samples exhibited superior electrochemical performance at a high cut-off voltage of 4.6 V.At the current density of 2 C,the specific discharge capacity of the first cycle of the NCM-La-F sample was 174.19 m Ah g^-1.After 150 cycles,the capacity retention rate was 91.05%,while the unmodified sample was only 72.60%.（3）The Li₂Mn O₃-coated Li Ni_0.6CO_0.2Mn_0.2O₂ was synthesized by the precursor coating method.As a result,7wt%Li₂Mn O₃ coated NCM samples showed the best electrochemical performance.At a current density of 0.5 C and a voltage range of 2.7 to 4.3 V,the capacity retention rate after 100 cycles reaches 93.94%.When the current density is increased to 5 C,the specific discharge capacity of 111.23 m Ah g^-1 still remains after 400 cycles,showing good cycle performance.The discharge specific capacity at a large current density of 10 C is 125.94m Ah g^-1,which is higher than the 109.49 m Ah g^-1 of pristine sample.