Structure Design And Performance Analysis Of Nickel Cobalt Lithium Manganate (NCM622) Cathode Material

With the rapid development of new energy industry,cathode materials for lithium-ion batteries have become the focus of the market and researchers.As one of the middle and high nickel based cathode materials,Li Co O₄has become a potential cathode material to replace the existing market due to its high specific capacity,simple synthesis process and high safety.However,the material has low capacity and poor cycle stability in practical use.At the same time,the side reaction with electrolyte in the long cycle process leads to serious phase transformation.Therefore,in this paper,the structure design based on density functional theory is combined with experimental verification,the doping structure is designed to improve the capacity of NCM622,the surface coating structure is designed to improve the cycle stability of NCM622,and the co modified structure is designed to improve the capacity and environmental protection of NCM622.Using material Based on the first principles（DFT）CASTEP module in studio software,the energy band,density of States,unit cell parameters,bond population and lithium ion diffusion barrier of different doping structure,coating structure and co modified structure are simulated and calculated,and the effects of doping structure,coating structure and co modified structure on the crystal structure and electrochemical performance of NCM622 cathode material are verified through experiments.The details are as follows:（1）The lattice model of NCM622 was constructed by using CASTEP module of material Studio Software Based on density functional theory,and the related experimental parameters of preparing NCM622 cathode material were determined.The calculated band gap of NCM622 crystal structure is 2.09e V and the density of states of lithium ion in NCM622 near Fermi level is very small.The relative freedom of lithium ion proves that NCM622 is suitable for cathode material of lithium ion battery.In the experiment,the sintering atmosphere was oxygen,the heating rate was3℃/min,the sintering process was optimized,and the optimal ratio of lithium source/precursor（Li/TM）was 1.15:1.（2）The structure model of doped NCM622 was established,and the doping effect was verified by lanthanum doping experiment.The effects of Mg,Zr,Mo and La doping on the electronic structure of NCM622 were analyzed by simulation.The band gaps of Mg,Zr,Mo and La doped NCM622 were 1.496e V 1.939e V 1.418ev and0.89e V respectively.The results show that the conductivity of NCM622 can be improved by La doping.La doped NCM622 was prepared.The results show that La doped structure can effectively reduce the Li Ni miscibility,and the content of Ni²⁺is also significantly reduced.0.3wt%La doping can increase the capacity of NCM622from 185m Ah/gto 206m Ah/g at 0.1C current density.（3）The structure model of coated NCM622 was established,and the coating effect was verified by lithium lanthanum oxide coating material.The influence of the structure of lithium tungstate（Li₂WO₄）,lithium phosphate（Li₃PO₄）and lithium lanthanum oxide（Li La O₂）adsorbing NCM622 on the electronic structure was analyzed by simulation calculation.The lithium ion diffusion barriers of Li₂WO₄,Li₃PO₄and Li La O₂adsorbing materials were 0.72e V 0.58ev and 0.34e V respectively,which indicated that the lithium ion diffusion performance of the materials could be effectively improved after lithium lanthanum oxide adsorption.The results show that the cycle retention rate of La coated NCM622 increases from 76%to 92%after 50cycles at 0.1C.（4）The structure model of lanthanum doped lithium lanthanide adsorbing NCM622 was established,and the cathode material of NCM622 coated with lanthanum doped lithium lanthanide was prepared to verify the effect of co modification.The calculated band gap of the co modified structure model is only0.1e V which indicates that the co modified method further improves the conductivity of the material.In order to verify the actual effect of the co modified structure on the capacity and structural stability of the material,the test voltage was increased from4.4V to 4.6V.It was found that the retention rate of the co modified material after 200cycles was higher than 78%at 1C current density.Compared with 34%retention rate of the unmodified material,the cycle stability of the material was greatly improved.At the same time,the specific capacity is increased from 185 to 212 m Ah/g.In conclusion,the doped coating structure can effectively improve the capacity and cycle stability of NCM622.