Synthesis And Modification Of Manganese-based Lithium-rich Oxide Cathodes

The lithium ion battery has the advantages of high energy density and long cycle life,which are mainly used in portable electronic devices and electric vehicles.However,LiCoO2,LiNixCoyMnzO2,LiFePO4 and LiMn2O4,which are difficult to meet the high energy density.Developping some cathode materials with high energy density is very important.In recent years,lithium-rich oxide cathode material xLi2MnO3·(1-x)LiMO2(0<x<1,M=Ni,Co,Mn)due to its high specific capacity(250-300mAh/g),high voltage platform of charge-discharge(>4.5V),which have become a research hotspot.The precursor of Ni0.5Co0.3Mn0.2(OH)2 was prepared with the hydroxide co-precipitation method.The effects of reaction atmosphere,sintering temperature and solid content on the morphology,crystal structure and electrochemical properties of the materials were studied.The synthesized samples were analyzed by X-ray powder diffraction(XRD),scanning electron microscope(SEM)and electrochemical performance.The results showed the morphology of precursor is normalized,the particles were dense,and the synthesized cathode material has good electrochemical performance under the argon atmosphere,and the solid content at 5%.The electrochemical properties of LiNi0.5Co0.3Mn0.2O2 and LiNi0.5Co0.3Mn0.2O2-graphene were studied by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy.The results show that the initial discharge capacity of LiNi0.5Co0.3Mn0.2O2-graphene composites is up to 203.86 mAh/g,and the impedance of Ret is reduced,which has better electrochemical performance.A series of lithium-rich oxide cathode material xLi2MnO3·(1-x)LiNi0.5Co0.3Mn0.2O2(x-0.4,0.5,0.6,0.7)were prepared by co-precipitation method,and the synthesized samples were analyzed by scanning electron microscopy(SEM),X-ray powder diffraction(XRD),cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS).The results of XRD showed that the space group of the samples were R-3m.The results of electrochemical performance test showed that the first charge discharge of 0.6Li2MnO3·0.4 LiNi0.5Co0.3Mn0.2O2 is up to 289.69mAh/g at 0.1C,and the discharge capacity is up to 190.72mAh/g at 1C,the capacity retention rate was 95.1%after 50cycle,but the discharge capacity decreased significantly at 2C after 50cycle.And the electrochemical performance of 0.5Li2MnO3·0.5LiNi0.5Co0.3Mn0.2O2 is best at 2C after 50cycle,which still hold 153 mAh/g.The high rate performance of 0.6Li2MnO3·0.4LiNi0.5Co0.3Mn0.2O2 has been improved by the sol-gel coating of Al2O3.