Preparation And Surface Modification Of Lithium-ion Battery Cathode Material LiMn_1.5Ni_0.5O₄

In this paper,we focus on preparation and surface modification of LiNi_0.5Mn_1.5O₄cathode material for lithium-ion batteries.LiNi_0.5Mn_1.5O₄ cathode material was prepared by co-precipitation and solid phase method,and lithium nickel manganate was coated to improve its electrochemical performance.The properties of materials prepared by different experimental methods were compared.The sample prepared by coprecipitation method has uniform particle size about 1 micron,complete octahedron shape characteristics,smooth surface clear outline and good crystallinity;the sample prepared by solid phase method also has octahedron shape,but the particle uniformity is relatively poor,particle agglomeration phenomenon is obvious,and some particle outlines appear blurred.The first charge-discharge capacities of samples prepared by coprecipitation at current rate in 0.1C and 1C were 115.08 mAh/g and 108.32mAh/g,respectively,while those prepared by solid-phase method were 103.71 mAh/g and87.74 mAh/g,respectively.The samples prepared by coprecipitation method showed better electrochemical performance.The properties of LiNi_0.5Mn_1.5O₄ coated with 1%,1.5%and 2.5%ZnO were compared.The results show that the coating has no effect on the structure of the matrix material.The electrochemical performance of materials coated with 1.5%ZnO was improved significantly at room temperature,the first discharge specific capacity was 133.15mAh/g at 0.1C current rate,and the capacity retention rate was 96.1%after 100 charge-discharge cycles;the first discharge specific capacity at room temperature was 132.66mAh/g at 1C current rate,and 90.1%after 100 charge-discharge cycles;the first discharge specific capacity was 126.96mAh/g at55?,and the charge-discharge specific capacity was 96 mAh/g at 1C current rate.After 100cycles,the capacity retention rate can still reach 77.2%.By further coating graphene oxide with 1.5%ZnO,it was found that the volume of the single agglomerated sphere formed by the coated particles decreased and the structure of lithium nickel manganate crystal remained unchanged.The results of electrochemical performance analysis show that the first discharge specific capacities of LNMO@ZnO coated and uncoated graphene oxide are 136.41 and 133.15 mAh/g,respectively,at 0.1C current rate at room temperature.Graphene oxide coated with graphene oxide can improve the capacity performance at high rate,reduce the resistance of lithium ion migration from SEI film and reduce the impedance.Graphene oxide coated at high temperature can still enhance the conductivity of matrix,showing better electrochemical performance.Through research and analysis,we can see that coprecipitation method has a long preparation period and higher cost,but better performance,while solid phase method is suitable for industrial production.The process of coating zinc oxide is simple,the preparation period is short and the preparation cost is low.The research of graphene oxide coating process still needs to be further optimized.