Design,Preparation And Electrochemical Properties Of LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Materials With Different Core-shell Structures

In recent years,layered Ni-rich cathode materials have been widely studied due to the advantages of high capacity,good cycling performance and low cost.Ni is the main active element.The higher the content of Ni content is,the higher capacity is,but the cycling stability and thermal stability become worse with it.While Co,Mn play role in stabilizing the lattice structure.The higher Mn content is,the better the stability is,but it will lead to the decrease of material capacity.Therefore,the capacity,cycle life and thermal stability of Ni-rich cathode materials are mutually restricted,which affects the large-scale application of Ni-rich cathode materials.It has been proved that the core-shell structure design?Take Ni-rich component as core to give high capacity,and take Mn-rich component as shell to give to high stability?is an effective method to modify the Ni-rich cathode materials to combine high capacity,long life and high thermal stability.However,the current research is only limited to the comparison between core-shell structure materials and homogeneous materials.There is a lack of research of the influence on different core-shell structure design on the structure and electrochemical properties of cathode materials with the same total composition..Based on this,this paper takes LiNi_0.6Co_0.2Mn_0.2O₂?NCM622?as the research object,and adopts different core-shell structure designs to compare and study the differences of structure and electrochemical properties of materials with different core-shell structure designs,which will be helpful to further explore the design and modification of core-shell structure cathode materials.Firstly,according to the phase diagram,core component with gradually decreasing Ni content and shell component with gradually increasing Mn content were selected in thepurephasearea.LiNi_0.6Co_0.2Mn_0.2O₂isredesignedinto Li[?Ni?0.4?Ni0.33Co0.33Mn0.33?0.6]O2,Li[?Ni0.80Co0.2?0.5?Ni0.40Co0.2Mn0.4?0.5]O2and Li[(Ni_0.67Co_0.33)_0.6(Ni_0.5Mn_0.5)_0.4]O₂.The element distribution of the cross-section shows that the designed core-shell structure cathode material has been successfully prepared.The results show that Li[(Ni_0.80Co_0.2)_0.5(Ni_0.40Co_0.2Mn_0.4)_0.5]O₂ material has the best comprehensive performance.The main reason is that LiNi_0.40Co_0.2Mn_0.4O₂ shell material provides excellent ionic conductivity and structural stability,and the appropriate core-shell structure combination ensures the exhibition of LiNi_0.80Co_0.2O₂core material capacity.Secondly,on the basis of optimizing the structure composition of core and shell,the structure and electrochemical properties of NCM622 cathode material were further modified by double shell structure design.The effect of different nuclear layer composition on the structure and electrochemical performance of NCM622 positive electrode material was studied.In the experiment,LiNi_0.40Co_0.2Mn_0.4O₂ with high stability act as shell,and still using LiNiO₂-LiCoO₂-LiMnO₂ phase diagram,LiNi_0.25Co_0.5Mn_0.25O₂ is added and act as a transition layer.LiNi_0.9Co_0.1O₂,LiNi_0.9Co_0.05Mn_0.05O₂,and LiNi_0.8Co_0.1Mn_0.1O₂ are respectively used as core materials to optimize the synthesis of double-core-shell structure materials.The results showed that the double-core-shell structure with LiNi_0.8Co_0.1Mn_0.1O₂ as the core exhibit the best electrochemical properties.This may be due to the LiNi_0.8Co_0.1Mn_0.1O₂ material with better balance between capacity and structural stability,and is more suitable to be used as core in core-shell structure materials.