Investigation Of Synthesis And Modification Of High Energy Density Cathode Material With Layer Structure For Lithium Ion

Ternary materials are the mainstream of R&D and industrialization in the next five years,and they are also the potential cathode materials for the next generation of high-energy-density lithium ion batteries and electronic products.In particular,high-nickel cathode materials,with higher capacity?>180mAh/g?and relatively low cost,has attracted wide attention from academic and industrial circles.However,high-nickel materials have structural defects and strong activity of surface,which restricts the practical application of the material.To deal with these problems,In this dissertation,the effect of cation substitution on structural defects and surface reactions of high nickel cathode materials was investigated.As well as improving the electrochemical performance of high nickel cathode material surface by NH₄F surface modified.?1?In this work,we select four types of substitute cations,Ti⁴⁺,Al^3+,Mg²⁺and Zn²⁺,to compare their influence on LiNi_0.8Co_0.1Mn_0.1O₂.After modification,the average lengths of Ni-O bonds are elongated with the turn of the Ti-,Al-,Mg-,pristine and Zn-substituted,namely the bond energies are diminished with this sequence,according to their roughly inverse square relation.This tendency is also obeyed by oxygen defects,which induces the Ni-Li exchanging and surface decomposition,and then exert the effect on electrochemical behavior of Ni-rich cathodes.Among the investigated samples,the Ti-modified sample,which possesses the highest Ni-O bond energy,presents the best cyclic stability and rate capability,retaining 93.8%in the 200^th cycle and 155.1 mAh g^-1under 5C,which is¹2%higher than the pristine sample.Our approaches illustrate the importance of Ni-O network and provide a novel thought to further improve these promising cathodes.?2?the outer part of the cathode particle is contaminated with moisture and CO₂ from contact with the air,thus forming LiOH and Li₂CO₃.For these reasons,the pH value of Ni-rich compounds in powder form in water is usually over 12,which results in rapid formation of a composites gel in NMP solvent.In addition,Li₂CO₃ tends to react with LiPF₆-based electrolyte to generate gases.In this paper,the NH₄F was used to modify the Ni-rich surface.The NH₄F reacted with the by-products on the surface of the high-nickel material to form in-situ LiF-coated high-nickel cathode materials.Under the condition of 2%NH₄F,the material has the best electrochemical performance,retaining 143.9 mAh g^-1 in the 300^th cycle.This method has a simple synthesis process,strong operability,and has a certain industrial application value.