Synthesis And Performance Research Of Lithium-rich Manganes Based Material For Lithium-Ion Battery

Li-rich cathode material has attracted many scholars’ attention because of its favorable advantages of high voltage,high specific capacity and non-pollution.The Molecular formula can expressed as xLi2MnO3·(1-x)LiMO2(0<x<1,M=Ni、Co、Mn),and it expected to become the next generation of high energy density lithium ion electrode materials.However,the disadvantages keeping back its application,such as low initial coulomb,rate property and cycle stability.To solve those problems,Acid treatment,transition metal ion-doped and surface modification were propose by many scholars.However,the structural stability and Ion/electronic diffusion coefficient of cathode material result in setbacks when using the above methods.In this work,we use fast ion conductor LLTO as Coating agent which can keep the structural stability and improve Ion/electronic diffusion coefficient of cathode material.The Buffer layer can suppress corrosion effect between cathode and electrolyte.The contents of this research as follow:First,the Li-rich cathode hydroxyl precursor was preparation by coprecipitation while discuss influence factors to electrochemical properties such as Sintering temperature,pH scope and the percentage of transition metal.The TG,XRD,SEM and constant current charge-discharge tests analysis shows the material has the excellent electrochemical properties when Sintering temperature is 900℃,precursor coprecipitation pH from 11 to 11.5,transition metal M represents Ni0.5Co0.2 Mn0.3.In the first charge-discharge specific capacity is 323.6mAh/g and 245.3mAh/g,respectively.And the Coulomb efficiency is 76.46%.The capacity retention of the sample is 93.64%after 60 time cycle which lost 15.6mAh/g comparatively with first discharge.Second,the 0.6Li2MnO3·0.4LiNi0.5Co0.2Mn0.3O2 was coated by Li0.34La0.51TiO3 which belong to fast ion conductor.And the adjustment the percentage of Li0.34La0.51TiO3 as 1%、3%and 5%.The physical and electrochemical performances of pristine and Li0.34La0.51TiO3-coated 0.6Li2MnO3·0.4LiNi0.5Co0.2Mn0.3O2 cathode materials are investigated by X-ray diffraction(XRD),scanning electronmicroscopy(SEM)and Electronic Differential System(EDS)measurements.The result indicative than the crystal structure of 0.6Li2MnO3·0.4LiNi0.5Co0.2Mn0.3O2 has not changed and the surface of 0.6Li2MnO3·0.4Li Ni0.5Co0.2 Mn0.3O2 has coated with a Li0.34La0.51TiO3 layer.The coated 0.6Li2MnO3·0.4LiNi0.5CoO.2Mn0.3O2 with 1 wt%Li0.34La0.51TiO3 and pristine sample displays capacity fade of 11.1mAh/g and 19.2mAh/g,respectively,after 80 and 60 cycles,with the capacity retention of 95.42%and 92.2%.Third,the 0.6Li2MnO3·0.4LiNi0.5Co0.2Mn0.3O2 was coated by Li0.34La0.46Sr0.05TiO3 through the hydrothermal method.And the adjustment the percentage of Li0.34La0.46Sr0.05TiO3 as 1%、3%and 5%.The crystal structure,Surface morphology and Electronic Differential System measurements revealed than the diffraction peak of 0.6Li2MnO3·0.4LiNi0.5Co0.2Mn0.3O2 has not change and the surface of 0.6Li2MnO3·0.4Li Ni0.5Co0.2 Mn0.3O2 was coated with a Li0.34La0.46Sr0.05TiO3 layer.The initial charge-discharge profiles of pristine and Li0.34La0.46Sr0.05TiO3-coated sample are strikingly similar which indicate Li0.34La0.466Sr0.05TiO3 coating layer do not change the Li+intercalation and deintercalation mechanism.The investigation on their electrochemical performance demonstrates that 1%Li0.34La0.46Sr0.05TiO3-coated 0.6Li2MnO3·0.4LiNi0.5Co0.2 Mn0.3O2 exhibits the best performance,with the capacity retention of 81.17%after first cycle much better than 76%which belong to pristine materials.The capacity retention of 1%,3%and 5%Li0.34La0.46Sr0.05TiO3 coating sample is 98.48%,96.74%and 91.91%after 80 cycles,respectively.Cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)confirm that Li0.34La0.51TiO3 and Li0.34La0.46Sr0.05TiO3 coating layer can improve stability of Li-rich cathode material owe to suppress side effects between electrolyte and the active material.In addition,the fast ion conductor coated layer can reduces the charge transfer resistance which increased the rate of Li+diffusion.