Optimization Of Preparation And Silicotungstic Acid Coating For Lithium-rich Manganese-based Cathode Materials

Lithium-rich manganese-based layered cathode materials of Li-ion batteries have become a research hotspot for many scholars because of high specific capacity,low cost and simple synthesis process.However,in order to apply this material to commercial production,it is also necessary to solve problems such as low initial Coulomb Efficiency,poor cycle and rate stability and so on.The main content of this paper is to synthesize new type of high operating voltage lithium-rich cathode material 0.5Li₂MnO₃×0.5LiNi_0.8Co_0.1Mn_0.1O₂ via co-precipitation method combine with high temperature solid phase technology,at the same time,optimizing the key parameters of synthesis process.The finally obtained lithium-rich cathode materials compare with the widely studied 0.5Li₂MnO₃×0.5LiNi_1/3Co_1/3Mn?1/3?O₂ to analyze the advantages and disadvantages of 0.5Li₂MnO₃×0.5LiNi_0.8Co_0.1Mn_0.1O₂ material.In addition,aiming to improve the cycle stability and rate performance,we studied the silicotungstic-acid coating on the surface of of Li-rich cathode material 0.5Li₂MnO₃×0.5LiNi_1/3Co_1/3Mn_1/3O₂,and in-depth exploring the influence of structural and electrochemical performance after silicotungstic-acid coating by physical analyze and electrochemical characterization.On account of low average operating voltage of Li-rich cathode material 0.5Li₂MnO₃×0.5LiNi_1/3Co_1/3Mn_1/3O₂,and the phase transition is easily happened during the charge/discharge process,leading to the capacity and voltage decay.So it is intended to reduce the content of transition metal Mn of materials,preparing the lithium-rich manganese-based layered cathode materials with the composition of 0.5Li₂MnO₃×0.5LiNi_0.8Co_0.1Mn_0.1O₂,to increase the average operating voltage of material.And optimizing the presintering time,calcination temperature and calcination time of synthesis process,to make sure the best synthesis technology of lithium-rich 0.5Li₂MnO₃×0.5LiNi_0.8Co_0.1Mn_0.1O₂ by XRD,SEM and other physical characterization combined with electrochemical performance,the materials show high initial discharge capacity of 149 m A h g^-1 and superior average operating voltage with 3.86 V.At the same time,the obtained lithium-rich materials 0.5Li₂MnO₃×0.5LiNi_0.8Co_0.1Mn_0.1O₂ with optimum synthesis process compare with 0.5Li₂MnO₃×0.5LiNi_1/3Co_1/3Mn_1/3O₂ sample.The 0.5Li₂MnO₃×0.5LiNi_0.8Co_0.1Mn_0.1O₂ material has significantly improved on rate performance and voltage decay during cycling,the discharge specific capacity is still 114 m A h g^-1 at the current density of 1000 m A g^-1,and the voltage is only 0.07 V after 100 cycles at 1 C rate,comparing with the _0.17 V of 0.5Li₂MnO₃×0.5LiNi_1/3Co_1/3Mn_1/3O₂ material.Because the Li₂MnO₃ phase in lithium-rich manganese-based layered cathode materials 0.5Li₂MnO₃×0.5LiNi_1/3Co_1/3Mn_1/3O₂ is an insulator,which is not conducive to electron and ion transmission,leading to lower the overall rate performance of the materials.Therefore,silicotungstic-acid with high electron and ion conductivity coated on the surface of the material to improve the overall electronic conductivity and lithium ion diffusion coefficient,further enhancing the rate performance of materials,the discharge specific capacity of coated materials is still 158 m A h g^-1 at the current density of 500 m A g^-1,which is higher about 34 m A h g^-1 than the original material.Meanwhile,silicotungstic-acid as a surface protection layer,can effectively inhibit the secondary reaction between the electrode material and electrolyte,improving the interface structural stability,leading to the superior cycle performance of lithium-rich manganese based cathode materials,at the current density of 300 m A g^-1,capacity retention of coated material is still over 90% after 100 cycles.