Synthesis And Electrochemical Properties Of The Li-rich Mn-based Cathode Material Li[Li_0.20Ni_0.15Mn_0.55Co_0.10]O₂

Lithium-ion batteries?LIBs?have exhibited the higher energy densities than other commercialized batteries and have been widely used in many applications.However,the imbalance of the materials' capacity at cathode(<250 mAh g^-1)and anode(1000 mAh g^-1)has badly limited the capacity of the whole battery.Recently,the lithium-rich layered oxides?LLOs?Li[Li_xM_1-x]O₂(M=Ni,Co,Mn,Ni_1/2Mn_1/2...),which are also denoted as xLi₂MnO₃·?1-x?LiMO₂,have drawn lots of attention due to their excellent theoretical discharge capacity,high working potential,high energy density(1000 Wh kg^-1),low cost and environmental benignity.However,the lithium-rich manganese-based cathode materials also have some disadvantages,such as capacity fading,voltage decline,inferior rate capability and low initial coulomblic efficiency during the first cycle,which greatly hinder their large-scale applications.In order to address these drawbacks,several methods have been proposed,such as compositional tailoring,synthetic strategy and advisable modifications.The primary research contents and conclusions of this thesis are summarized as below:?1?Lithium-rich Mn-based ternary cathode material Li[Li_0.20Ni_0.15Mn_0.55Co_0.10]O₂ was synthesized by the solvothermal method and sol-gel method,respectively,and the suitable synthesis system was determined.The result showed that the sample prepared by the sol-gel method had a higher discharge capacity,better cyclic stability and rate performance,and lower impedance and larger diffusion coefficient.Then,the properties of the material were further improved by controlling the conditions of the sol-gel method.It implied that the title material with the best performance could be obtained under the following conditions:?i?the sintering temperature of 850 0C;?ii?using pvp?K23-26?as the chelating agent and?iii?the molar ratio of metal ions to pvp being 1.5.?2?The carbonization-reduction modification was performed on the surface of the material obtained in?1?.After the introduction of the spinel phase on the surface of the material,the material showed improved initial discharge capacity,rate performance and excellent cycling stability due to the 3D diffusion channel and surface protection of the newly-formed spinel phase.A high initial coulombic efficiency of 88.7%was obtained at 0.1 C.After cycling at 0.5 C and 1 C,discharge capacities of 239.37 mAh g^-1 and 235.87 mAh g^-1 can be delivered,respectively.?3?The Al₂O₃ coating on the surface of the original material obtained in?1?was conducted and the coating amount was controlledted.The influence of the Al₂O₃ coating on the electrochemical properties of the material was investigated.It was found that the sample with a coating amount of 2%showed a higher discharge capacity and a better cycling stability.