The Research On Preparation And Coating Modification Of LiNi_0.5Mn_1.5O₄ Cathode Material

In the exploration of lithium ion battery cathode materials,spinel LiNi _0.5Mn_1.5O₄materials have become the preferred cathode material for power supply because of the advantages such as high energy density and high power density.In order to further meet the application of lithium-ion batteries in the field of high-power equipment and improve the material's rate performance,it is necessary to further improve the transfer rate of lithium-ions.The study found that transfer rate of lithium ions could be improved effectively between nano-sized LiNi_0.5Mn_1.5O₄ particles,but the corrosion of the material surface also be accelerated due to the excessive contact area of nano-sized materials,thereby reducing the life of the battery.At the same time,the low crystallinity of the nanoparticle leads to the low electrochemical activity of material and the decrease in discharge capacity.If a micro sized spherical structure formed by the agglomeration of nano-sized particles can be obtained,the excellent kinetic advantages of the nano material and the macroscopic stability of the micro-material can be taken into consideration,and the comprehensive performance of the battery will be further improved.In this thesis,nano-micro spherical materials with hollow structure were synthesized by co-precipitation method.Subsequently,the effect of the amount of ethanol to the morphologies,sizes,crystallinity and electrochemical properties of the materials were studied by adjusting the proportion of water/ethanol in the solvent system.It is founded that with the proportion of ethanol increased in the solvent system,the size of the spherical structure,the sphericity and the degree of agglomeration were all reduced.At the same time,the primary particle size of the spherical struct ure and the crystallinity were increased.When the mixing ratio of water and ethanol in the reaction solvent system was 4:1,the prepared material displayed the best electrochemical performances,and the material could provide a discharge capacity of116.7 mAh g^-1 at the rate of 10 C.The capacity retention was 92.4%after 100 cycles at the rate of 0.2 C,it was considered that the excellent electrochemical performance was attributable to the high crystallinity of the primary particles and the high stabili ty provided by the hollow structure.Finally,on the basis of excellent rate performance,in order to further improve the cycle stability of the material,Al₂O₃ was selected as the coating material to modify the material.The effects of different coating amounts on the electrochemical properties of the materials were also investigated.Electrochemical tests results showed that the Al₂O₃ coated LiNi_0.5Mn_1.5O₄ cathode material with coating mass ratio of 1 wt%have the best electrochemical performances.The initial discharge capacity of the material at0.2 C was 133.7 mAh g^-1,and the capacity retention can reach 97.7%after 100 cycles.This can be attributed to the uniform and dense Al₂O₃ coating on the surface of the material,which avoid the direct contact between the material and the electrolyte,thus reduces the corrosion of the electrolyte surface effectively and prolongs the cycle life of the battery.