Modified Research Of Lithium-rich Manganese-based Cathode Material Li_1.2Ni_0.13Co_0.13Mn_0.54O₂

Lithium-rich manganese oxide(1-x)Li₂Mn O₃·x Li MO₂ has attracted much attention due to its high initial discharge capacity(>250 m Ah g^-1)and is considered as the most promising next-generation commercial cathode material.However,the problem of irreversible lattice oxygen escape during the initial cycling leads to low initial Coulomb efficiency,rapid capacity and voltage decay,and poor multiplicity performance of the cathode material,which limits its practical application.Based on above questions,Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ is studied in this paper,and its systematic modification by doping and interfacial modification is aimed at stabilizing the structure while regulating the lattice oxygen activity and improving the electrochemical properties of the material.The main studies are as follows.:(1)A method was used to modify the lithium-rich manganese cathode material by generating a double spinel shell layer in situ on the surface of the lithium-rich manganese cathode material to improve interfacial stability.The in situ prepared double spinel shell layer can effectively inhibit the phase transition from layered to spinel phase.Li Co Mn O₄ coating layer can also effectively mitigate the side reactions between the host material and the electrolyte.The electrochemical results show that the composite achieve good electrochemical performance as the coating amount of Li Co Mn O₄ is 5mol%,and the capacity retention is 92.7%after 100 cycles at 0.2 C.The fitting results of XPS and other analyses show that the excellent electrochemical performance of the composite is related to the effective inhibit irreversible lattice oxygen loss from the lithium-rich manganese cathode material during the initial charging process by the double spinel shell heterostructure.This indicates that the double spinel shell heterostructure is beneficial to improve the interfacial and structural stability of the lithium-rich manganese cathode material.In addition,the unique three-dimensional channels for Li⁺diffusion in the spinel shell layer also enhance the rate performance of lithium-rich manganese cathode material.(2)The lithium-rich manganese cathode secondary spherical particle with high exposure ratio of(010)crystal plane was prepared by hydroxide co-precipitation combined with high temperature solid phase method,and the electrochemical performance was compared with lithium-rich cathode materials prepared by carbonate co-precipitation method.Since the(010)crystalline plane of the lithium-rich cathode is an Li⁺intercalation/deintercalation channel,the prepared lithium-rich manganese cathode materials with high exposure ratio of(010)crystalline surface have good rate performance.Meanwhile,W doping lithium-rich manganese cathode materials with high exposure ratios of(010)crystal plane were synthesized by direct doping of precursors through a co-precipitation method.The structural and electrochemical analyses show that W elements can be doped into the lattice of lithium-rich manganese cathode materials and have strong covalent bonds with O,which can effectively inhibit the irreversible lattice oxygen loss,improve the structural stability,and thus suppress the capacity fade and voltage decay during cycling.(3)Based on the above study,Li-rich@spinel@Li₂WO₄ composites were prepared by surface coating and in situ induction using W doping lithium-rich manganese cathode materials with high exposure ratio of(010)crystalline planes as the base material.The results showed that the spinel interlayer and Li₂WO₄ coating layer could effectively inhibit the side reactions between the host material and electrolyte and improve the interfacial stability of lithium-rich manganese cathode materials.In addition,both the three-dimensional structure of the spinel phase interlayer and cubic tunneling structure of the Li₂WO₄ coating layer are conducive to the Li⁺diffusion,thus improving the rate performance of lithium-rich manganese cathode materials.The Li-rich@spinel@Li₂WO₄ material modified by the integrated strategy exhibited good electrochemical performance.In conclusion,lithium-rich manganese-based oxides Li_1.2Ni_0.13Co_0.13Mn_0.54O₂were investigated for structural and electrochemical performance improvement by doping and interfacial modifications in this thesis,respectively.Through the comparative study of the structural and electrochemical properties of the lithium-rich manganese-based materials before and after modification,it was found that the co-modification strategies of W doping and interfacial heterostructures can effectively improve the structural stability and lattice oxygen activity.And these studies provide new ideas to improve the modification of lithium-rich manganese-based cathode materials.