Preparation And Modification Of Nickel Based LiNi_0.6Co_0.2Mn_0.2O₂ Ternary Cathode Materials

In recent years,the increasing environmental pollution and the excessive consumption of non-renewable fossil energy,promote the development and utilization of green renewable energy.Lithium ion battery has the advantages of green and high efficiency,and can be used as the power source of many electronic products and new energy vehicles.Lithium ion ternary cathode materials combine the advantages of various cathode materials and attract extensive attention and research.Nickel based ternary cathode materials LiNi_0.6Co_0.2Mn_0.2O₂ have become one of the most promising cathode materials in the field of power battery due to its high theoretical capacity and good safety performance.However,due to the higher content of nickel,cation mixing is more likely to occur in the material,and the stability of layered structure is decreased,which affects the cycle stability and rate performance of the material.In order to solve the above problems,nickel based ternary cathode materials LiNi_0.6Co_0.2Mn_0.2O₂ was prepared by ball milling spray drying method.The effects of different calcination temperature and time,pretreatment pressure and Na ions doped with different ratios of the NCM622 cathode materials were investigated.The main research work are as follows:（1）NCM622 cathode materials were prepared by ball milling spray drying method.Based on previous work,the effects of calcination temperature and time on the structure and electrochemical properties of the materials are further explored.When the second calcination temperature is 900℃and the calcination time is 10 h,the structure of LiNi_0.6Co_0.2Mn_0.2O₂prepared by high temperature heat treatment precursor is the most regular,and the cation mixing effect is the lowest;the electrochemical performance is the best.After 150 cycles of 1C cycle,the discharge specific capacity decreases from 138.7 m Ah g^-1 to 126 m Ah g^-1,and the cycle retention rate is 90.8%.（2）On the basis of the optimal process,the effects of different pressures on the crystal phase,microstructure and electrochemical properties of NCM622 are studied.The results show that the mixture of lithium and nickel is reduced,the particle distribution is more uniform and the diffusion channel of lithium ion is widened.At 0.5C and 10C rates,the specific capacities of the samples pressed at 3Mpa are168 m Ah g^-1 and 130 m Ah g^-1,respectively.After 150 cycles at 10C,the retention rate remained above 85.1%.（3）Using the same method and the optimal process parameters,Na doped Li_1.05-xNi_0.6Co_0.2Mn_0.2Na_xO₂（x=0,0.005,0.01）cathode materials are synthesized.The effects of ion doping on the microstructure and electrochemical properties of the materials are investigated,and the optimal Na doping amount was explored.When x=0.005,the material structure becomes more stable.The discharge specific capacity of 0.5%sodium doped NCM material exhibits 155.4 m Ah g^-1 at 1C,while the capacity of the original sample delivers only 136.3m Ah g^-1.After 150 cycles at 5C,the retention rate increased from 49.4%of pure samples to73.7% of Na doped samples.