The Research On Preparation Of Lithium Rich Cathode Material And Its Performance Improvement

Lithium rich manganese based material is a new type of cathode material with high specific capacity and high working voltage,but it has high irreversible capacity and low electronic conductivity.Therefore,it can not get ideal high power performance.Due to the special discharge mechanism of lithium rich materials,the first cycle efficiency is low,which seriously hinders its practical application.Therefore,it is necessary to optimize the synthesis process to improve the electrochemical performance of lithium rich manganese based cathode materials.In this paper,the ball milling,spray drying and high temperature calcination process is used to prepare the target product.Compared with the coprecipitation method,this method does not produce large amounts of wastewater containing acid ions.It is a green and environmentally friendly synthesis technology.Moreover,the process simplifies the production process,saves the production cost and is suitable for large-scale production.It is found that the particle size obtained by ball milling for 60 minutes is the smallest?D50=235 nm?,and the highest electrochemical data is obtained when the calcination temperature is 900 ?,that is,the discharge specific capacity of 223.4 m Ah·g-1 in the first cycle.Therefore,60 min milling time and 900 ? calcination temperature are the best synthesis parameters.On the basis of the optimum synthesis conditions,we designed Li Ni_0.5Mn_1.5O₄ material with spinel system added in Li_1.4Mn_0.61Ni_0.18Co_0.18Al_0.03O_2.4?LNCMAO?to improve the low first cycle coulombic efficiency of lithium rich phase itself,and carried out f-element substitution modification on spinel Li Ni_0.5Mn_1.5O₄ material before composite.After modification,Li Ni0.5Mn1.5O3.9F0.1?LNMOF?material was recycled for 50 cycles After that,there was still 174.9 m Ah·g-1,which was 49.6% higher than the unmodified one.According to the charge discharge data of lncmao and LNMOF,we found that the first cycle charge discharge capacity of the composite was 229.2 m Ah·g-1 and 215.4 m Ah·g-1,and the coulombic efficiency increased from 65.9%?LNCMAO?to 94.0%?composite sample?.Moreover,the composite also shows outstanding cyclic stability,which can reach 203.6 m Ah·g-1 after 50 cycles at 0.2C.Finally,Y₂O₃ surface modification is used to improve the surface state of Li_1.4Mn_0.61Ni_0.18Co_0.18Al_0.03O_2.4,and the first cycle coulombic efficiency and capacity retention rate of the material are studied.It was found that the charge discharge specific capacity of Y₂O₃ modified samples decreased,but the first cycle coulombic efficiency increased from 65.4%to 74.7%.The improvement of electrochemical performance is mainly reflected in that the specific discharge capacity of Y₂O₃/Li_1.4Mn_0.61Ni_0.18Co_0.18Al_0.03O_2.4 at10C is 32.9 m Ah·g-1 higher than that of the unmodified sample.After 50 cycles of 0.2C,the capacity retention rate of the sample increased to 92.9%.This is mainly due to the fact that Y₂O₃ modification will make HF in the electrolyte react with Y₂O₃ preferentially,thus reducing the occurrence of side reactions on the surface of active substances.