Study On Preparation And Coating Modification Of LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Material For Lithium-ion Batteries

Recently,the rapid development of Electric vehicles（EVs）has led to a great increase in the demand for a new generation of lithium-ion batteries with high specific capacity,low cost,better safety and reliability.Cathode material is an indispensable part of lithium-ion batteries.Therefore,improving and developing the multiple properties of Li-ion battery cathode materials is urgent and meaningful.In the development and research of high-capacity cathode materials,compared with traditional cathode materials such as Li Fe PO₄ and Li Co O₂,high nickel ternary cathode materials have the advantages of lower cost,superior safety properties and higher discharge capacity.Li Ni_0.6Co_0.2Mn_0.2O₂cathode material combines energy density and safety performance to stand out among the nickel rich ternary materials,it has catch numerous attentions from researchers.However,Li Ni_0.6Co_0.2Mn_0.2O₂ cathode material still exists some problems such as low coulombic efficiency for the first cycle,phase transition,corrosion by electrolyte,and poor thermal stability.These problems greatly decrease the batteries life and limit its further commercial applications.In response to the aforementioned series of problems,this paper has carried out the following works:In this paper,the influence of different lithiation ratios and calcination temperatures on the crystal structure,surface morphology and electrochemical properties of Li Ni_0.6Co_0.2Mn_0.2O₂ cathode material was investigated by high-temperature solid-phase calcination method.The best calcination process is:the molar ratio of Li OH·H₂O and Ni_0.6Co_0.2Mn_0.2（OH）₂ is 1.05:1,the mixture was heated at 500℃ for 5 h,then calcined at 850℃ for 15 h in an O₂ atmosphere tube furnace.The obtained Li Ni_0.6Co_0.2Mn_0.2O₂ cathode material has a good layered hexagonalα-Na Fe O₂ structure;the secondary particles are in a uniform spherical shape.The determination of the sintering system laid a good foundation for the subsequent research on surface coating modification.sThe LiTiO₂@Li Ni_0.6Co_0.2Mn_0.2O₂ composite material was successfully prepared by solvothermal method and low-temperature solid-phase method.Among the modified samples,the NCM-LTO0.5sample exhibited the best electrochemical performance.In the voltage range of 2.7-4.3 V,the discharge capacity at 0.1 C under 25℃is 206.63m Ahg^-1,and the capacity retention after 200 cycles under 1.0 C is 88.03%.All electrochemical properties of the material have been significantly improved by LiTiO₂ surface coating.These improvements are due to the three-dimensional lithium-ion diffusion channel of LiTiO₂,which can effectively increase the deintercalation/intercalation rate of lithium ions,thereby increasing the conductivity of lithium-ions.In addition,the LiTiO₂ coating layer protects the NCM material from direct contact with the electrolyte,thereby reducing the occurrence of adverse side reactions,extending the service life of lithium-ion batteries,and can further promoting the commercial development of Li Ni_0.6Co_0.2Mn_0.2O₂ materials.The Nb₂O₅@Li Ni_0.6Co_0.2Mn_0.2O₂ composite cathode material was successfully prepared by ball milling and low-temperature solid-phase method.The degree of cation mixing in the Nb₂O₅ nano-coated sample is reduced.In the voltage range of 2.7-4.3 V,the capacity retention after 200cycles at 1.0 C under 25℃is 92.36%,which is much superior than the pristine sample.In addition,under high temperature conditions（60℃）,the discharge capacity of the 0.5Nb O@NCM electrode material after 200cycles at 1 C remained at 178.03 m Ahg^-1,the thermal stability was significantly improved.This improvement can be ascribed in the strong bond energy of Nb-O,which providing good thermal stability,and the high-valence metal（Nb）can helpfully inhibit the release of lattice oxygen during heating process.The Nb₂O₅@Li Ni_0.6Co_0.2Mn_0.2O₂ composite material has a simple preparation process and low equipment requirements,which is beneficial to industrialized production.