Study On Synthesis Of LiNi_0.6Co_0.2Mn_0.2O₂ Single-crystal Cathode Materials For Lithium-ion Batteries

In recent years,with the rapid development of new energy vehicles,lithium-ion batteries with low cost and high energy density have been widely used.The cathode material is an important part that affects the performance of lithium-ion batteries,so the development of cathode materials with high energy density and long cycle life is crucial to the application and development of lithium-ion batteries.Layered ternary cathode materials have been widely concerned due to their high specific capacity,long cycle life and low cost,but layered ternary cathode materials still have some structural and interfacial problems that affect the performance of materials,which need to be further solved.In recent years,researchers hope to solve the problems of poor interface and mechanical stability of traditional secondary spherical morphologies by single crystallization of layered ternary materials.Therefore,this paper takes Li Ni_0.6Co_0.2Mn_0.2O₂ single crystal material as the research object,and conducts in-depth research on its synthesis conditions and synthesis methods.The specific research results are as follows:（1）Li Ni_0.6Co_0.2Mn_0.2O₂ single crystal material was synthesized by introducing Ba²⁺.At the same time,the samples with and without Ba²⁺were compared,and the results show that the introduction of 2000 ppm of Ba²⁺is conducive to promoting the appearance of single crystal morphology,and will not have a significant effect on the crystal structure of the material.After the introduction of 2000 ppm Ba²⁺,the electrochemical cycling performance of the sample was significantly improved,the initial capacity was 159.2 m Ah/g at 1C rate,2.8-4.3 V voltage window,and the retention rate after 200 cycles was 81.85%.The sample without Ba²⁺data is 165.6 m Ah/g,67.39%.In addition,further experiments were designed to study the role of Ba²⁺in the sintering system,and the mechanism explanation was obtained that Ba²⁺promotes the growth of single crystals by affecting the grain boundary energy of the material.（2）The effects of different sintering atmospheres（air,dry air and oxygen atmosphere）on the morphology,structure and electrochemical properties of Li Ni_0.6Co_0.2Mn_0.2O₂ single crystal materials were studied.The results show that air sintering is beneficial to the growth of single crystals,while oxygen atmosphere sintering is beneficial to further improve the electrochemical properties of the materials.The samples sintered in oxygen atmosphere have an initial capacity of 160.2 m Ah/g and a retention rate of90.01%after 130 cycles at 1C rate and a voltage window of 2.8-4.3 V,while the data of samples sintered with air and dry air are 140.1 m Ah/g,82.94%;153.5 m Ah/g,87.62%,respectively.At the same time,this paper further designs experiments to study the reasons why air sintering is beneficial to the growth of single crystals,and preliminarily draws the inference that CO₂ in the air reacts with Li⁺in the material,resulting in the formation of spinel phase in the material and promoting the growth of single crystals.（3）Based on the experimental results of Ba²⁺-assisted single-crystal synthesis,the trivalent large-radius ion Bi³⁺was selected to assist the synthesis of Li Ni_0.6Co_0.2Mn_0.2O₂ single-crystal materials,and the samples with different doping amounts of Bi³⁺were analyzed.The experimental results show that Bi³⁺can not only promote the growth of Li Ni_0.6Co_0.2Mn_0.2O₂ single-crystal material,but also will not affect the structural characteristics of the material.With the increase of Bi³⁺doping amount,the particle size of the single-crystal will further increase,and the particles of the material will be more and more dispersed.In addition,electrochemical tests show that the single-crystal material formed after the introduction of Bi³⁺can significantly improve the electrochemical cycle performance of the material.The sample with the introduction amount of Bi³⁺of 4000 ppm has the best cycle performance under the 1C rate and the voltage window of 2.8-4.3 V.The capacity is 158.9 m Ah/g,and the retention rate after 150 cycles is 88.67%;while the original sample data is164.9 m Ah/g,76.51%.31 figures,14 tables,124 references...