Preparation And Modification Of High-Voltage Lithium-ion Battery Cathode Material LiNi_0.5Mn_1.5O₄

LiNi_0.5Mn_1.5O₄?LNMO?with spinel structure is considered as one of the most attractive cathode material for the next generation high lithium-ion power batteries because of its high potential?⁴.7 V vs.Li/Li⁺?,large theoretical capacity(146.7 mAh g^-1)and low cost,and has three-dimensional lithium ion diffusion channel.However,LNMO is prone to side reactions with the electrolyte under high voltage,resulting in capacity decay.In view of the above problems,this paper first optimizes the preparation process of LNMO cathode materials,and investigate the effects of Mn³⁺content,crystal orientation and Ni/Mn ordering degree on the electrochemical properties of the materials through the modification research.LNMO single crystal particles with polyhedral morphology were prepared by sol-gel method,and the effects of pH value,heat treatment atmosphere and temperature on the properties of the materials were investigated.Through characterization and analysis,the sample obtained by heat treatment at 850?under air has the best electrochemical performance in the reaction system with pH 7.At 1 C current density,the first discharge specific capacity of the sample was 124.1 mAh g^-1,and there was still 120.2 mAh g^-1 after100 charge and discharge cycles,and the capacity retention was as high as 95.9%.In addition,LNMO samples with secondary spherical morphology were prepared by co-precipitation method.The secondary particle size was about 20?m,and the tap density was high,which is suitable for industrial production.The surface modification of LNMO polyhedral particles prepared by sol–gel method was stuied by synergistic modification strategies of surface Li₂ZrO₃ coating with surface Zr doping,and the amount of Li₂ZrO₃ was optimized.And the structure,morphology and electrochemical properties of the materials were characterized by XRD,SEM,TEM,FIB,constant current charge and discharge,cyclic voltammetry and other methods.The results show that partial Zr elements diffused into the LNMO surface after modification,and induced a small amount of Mn³⁺,but the bulk structure of the material is not changed.At the same time,the modified sample with the coating content of 2 wt%showed the best electrochemical properties.The first discharge specific capacity can reach 123.2 mAh g^-1 at5 C rate under room temperature,and the capacity retention rate after 1000 cycles is as high as 82.4%.Even under high temperature conditions,the capacity retention for 200 cycles increased from 61.1%to 83.5%at 1 C rate.The heterostructure LiNi_0.5Mn_1.5O₄@LiNi_0.5Co_0.05Mn_1.45O₄ cathode material was prepared by co-precipitation method and compared with LiNi_0.5Mn_1.5O₄ blank spherical sample.The results indicated that the crystal orientation of the primary particles of the two samples showed significant differences.At the same time,the heterostructure sample exhibited excellent high-rate and long-cycle performance,the discharge specific capacity can still reach 92.1 mAh g^-1 after 2000 cycles at a rate of 10 C,and the capacity retention rate was as high as 85.6%.