Study On Preparation And Modification Of Lithium-rich Cathode Materials For Lithium Ion Batteries

Lithium-rich manganese-based layered oxide cathode materials have received extensive attention due to their high specific capacity(>300 m Ah g^-1),high energy density(>1000 Wh kg^-1)and low cost.However,the commercial application of lithium-rich layered manganese-based oxide cathode materials faces several difficulties,including the poor cycling performance,the low initial coulomb efficiency,and the severe voltage attenuation.This thesis takes the lithium-rich layered manganese-based oxide cathode material as the research object,and the research contents are as follows:（1）First,the layered Li_1.2Ni_0.13Co_0.13Mn_0.54O₂（LLO）cathode material was prepared by the co-precipitation method,and modified by a layer of VOPO₄coating via wet chemical method and air low-temperature calcination method.It is found that VOPO₄has good ion conductivity and high crystallinity,and VOPO₄coating can not only reduce the residual Li⁺content on the surface of LLO,but also inhibit the structural degradation of LLO.At the same time,VOPO₄can inhibit O₂molecules from escaping from LLO during charge/discharge process,thereby improving electrochemical performance.The results show that the LLO sample modified by 3wt%VOPO₄has an initial discharge capacity of 260.5 m Ah g^-1at 0.1C and an initial coulombic efficiency of 99.57%at 1 C.After 100 cycles,the discharge capacity retention rate was 92%,showing good electrochemical performance.（2）Ce doped Li_1.2Ni_0.13Co_0.13Mn_0.54O₂cathode material is successfully synthesized by calcination method.It has been found that Li₂CeO₃spinel phase can be formed on the surface of the material.In addition,Ce surface doping cathode materials can effectively improve the cycle stability and rate capacity,especially the 3wt%Ce surface doped material shows better discharge performance after 100 cycles at 1 C.Capacity retention rate is 88%,and discharge capacity at 10C is 106 m Ah g^-1.（3）Ce and F co-doped Li_1.2Ni_0.13Co_0.13Mn_0.54O₂cathode material is successfully synthesized by means of calcining in oxygen atmosphere.It has been found that Ce and F ions can be successfully incorporated into the material crystal.The material modified by 3 wt%Ce and 1 wt%F shows better discharge capacity retention rate of89.6%after 100 cycles at 1 C,and discharge capacity at 10 C is still as high as 140m Ah g^-1.