Research On Preparation And Modification Of Single Crystal Ternary Cathode Materials For Lithium-ion Batterie

Due to its excellent characteristics such as high energy density,good cycling performance,high discharge voltage platform and good safety,high nickel cathode materials are widely used in wireless electronic products,power tools and electric vehicles.Among them,the traditional polycrystalline ternary cathode materials are usually secondary spherical polycrystalline particles formed by the aggregation of many nanoscale primary particles.Microcrack is one of the most common failure mechanisms of polycrystalline ternary cathode materials during the cycle.The generation of microcracks will increase the surface side reaction between electrode material and electrolyte,resulting in serious capacity loss.However,monocrystalline ternary cathode materials can solve a series of problems caused by microcracks in polycrystalline materials to a large extent because of the absence of intra-crystal cracks.In addition,because of its high compaction density,small specific surface area,smooth surface and other advantages,single-crystal terpolymer cathode materials are gradually studied and recognized by experts and researchers at home and abroad,and are also gradually applied commercially.However,single crystal materials also have some challenges,such as intercrystal micro-cracks and side reactions at the interface,especially under the condition of high cut-off voltage.In this paper,the preparation and modification of high nickel single crystal materials are studied and discussed.The detailed research contents and results are as follows:（1）The best sintering method was determined by combining high temperature sintering and low temperature holding,and the single crystal cathode material particles with the size of 1.5-3.5μm were prepared.The electrochemical results show that the single crystal cathode material prepared by sintering method of high temperature（900℃）and low temperature（800℃）shows excellent electrochemical performance.Under the voltage range of 2.8-4.3 V and 0.1 C,the specific discharge capacity of the first circle reaches 166.96 m Ah g^-1,and the corresponding Coulomb efficiency is88.91%.At the current density of 1 C,the capacity retention rate reached 93.19%(150.49-140.24 m Ah g^-1)after 100 cycles of charge and discharge.After 100 cycles,the electrodes were disassembled and characterized.It was further found that the excellent structure of the material was due to the inhibition of the side reaction of the interface during the sintering process at high temperature.（2）Select the rare earth element coating agent to modify the material,and test and analyze under the condition of 4.5 V high cut-off voltage.Sm₂O₃coating was performed on commercial Ni_0.6Co_0.1Mn_0.3O₂cathode material,and different sintering temperatures and coating amounts were investigated.XRD,SEM,HRTEM,XPS and other characterization methods have successfully proved the existence of coating layer on the surface of the material,and the existence of coating layer has no effect on the structure of the matrix material.The electrochemical results show that the material exhibits the best electrochemical performance when the sintering temperature is 500℃and the coating amount is 1 wt%.Under the condition of 0.1 C current density and3-4.5 V high voltage,the specific discharge capacity of the first ring reaches 200.38m Ah g^-1,and the corresponding Coulomb efficiency is 86.95%.1 C rate of 100 cycles after the cycle capacity still has 159.89 m Ah g^-1,capacity retention rate is 87.47%.Compared with raw material NCM,the increase was 10.46%.At the same time,the XRD and SEM characterization of the positive electrode plate after cycling further prove that the coating amount of Sm₂O₃is 1 wt%and the sintering temperature is500℃.The modified positive electrode material can inhibit the electrode/electrolyte side reaction to a large extent and has more excellent high voltage cycle stability.