Preparation And Electrochemical Performance Study Of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂,LMSO@Li_1.2Mn_0.54Ni_0.13Co_0.13O₂,NFO@Li_1.2Mn_0.54

Lithium ion batteries are widely used as an energy device in digital field because of its high working voltage,high energy density,non-toxic and pollution-free to environment.Due to the rapid development of pure electric vehicles and hybrid electric vehicle,requirements related with the energy density,working voltage,and the cost are put forward.The performance of lithium ion batteries is restricted with the cathode materials,anode materials and electrolyte,separator,among which the cathode materials matters most.The current cathode materials,such as LiCoO2,LiFePO4,Li2MnO4 are commercialized.However,limited by the capacity,cost and working voltage,the current cathode materials are far beyond the demand of pure electric vehicle and hybrid electric vehicles.Compared with the mentioned cathode materials,with high reversible specific capacity(250 mAh g-1),high voltage and low production cost,li-rich manganese-based layer oxide cathode materials(xLi2MnO3 LiMO2(1-x),0<x<1,M=Ni,Co,Mn)is regarded as the important one among the next generation candidates.But li-rich manganese-based layer oxide material has a larger initial capacity loss,rapid capacity loss caused by the phase change during cycle process and poor rate performance,which restrict its practical application.In this paper,to improve the performance of rich li-rich manganese-based layer oxide cathode material,the fast ion conductor La-Sr-Mn-0 and Ni2FeO4 are used to coat rich lithium manganese cathode materials,forming the core-shell sturcture,the results are shown as following:Considering the crystal structure of li-rich manganese-based layer oxide cathode material(Li1.2 Mn0.54 Ni0.13 Co0.13 O2)is easy to change under high temperature,losing the structure advantage thus affecting the electrochemical performance,we studied the influence of the coating temperature on its electrochemical performance and obtained the optimal one.Manganese acetate,lanthanum acetate,strontium acetate were used respectively for the source of manganese,lanthanum and strontium,ammonia as precipitant,LMSO coating li-rich manganese-based layer oxide cathode material were synthesized through co-precipitation method with the precursor sintering at different temperatures.The electrochemical performance test showed that the samples under 500℃ has excellent cycle performance and the best C-rate performance.The reversible specific capacity maintained 203.9 mAh g-1 at 1C after 200 cycles,with the capacity retention of 83.7%,revealing excellent cycle performance.However,the sample sintering under 600℃ underwent the structure change and the degradation of the electrochemical performance.With different mole ratio of manganese acetate,lanthanum acetate,strontium acetate as the source of manganese,lanthanum and strontium source source,ammonia as precipitator,LMSO li-rich manganese-based layer oxide cathode material of different mass were synthesized through co-precipitation method with the precursor sintering at 500℃.The electrochemical tests showed that the sample of 2%-coated exhibits excellent cycle performance and rate performance.The reversible specific capacity was maintained 134.3mAh/g,the capacity retention was 55.2%,much higher than that of the pristine sample.In the process of charging and discharging coating layer wrapped in lithium rich materials surface,reduce the corrosion of electrolyte on cathode materials and dissolution of manganese,avoid the transformation from layered 1 to spinel phase.The LR@Ni2FeO4 composite cathode material was prepared by co-precipitation method and solid phase method,nickel nitrate and ferric nitrate as the source of nickel and iron,and ammonia as precipitator.The characterization and electrochemical tests show that when the mass fraction of nickel ferrite is 3%(NF03),the composite exhibits excellent cycling performance.When the current density was 250mAh/g,the specific capacity was still maintained at 158.3mAh/g after 300 cycles,the capacity retention was higher than the pristine sample.In the cycling process,the coating layer is used as the buffer layer,so as to avoid the direct contact between the electrolyte and the lithium rich material,thereby reducing the dissolution of the material and improving the cycle performance of the material.