Modification Of Lithium-rich Cathode Material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ For Lithium-ion Batteries

With the increasing critical energy and environmental issues,the development for sustainable energy storage and conversation is of great importance in the world today.Among various secondary battery system,lithium-ion batteries have been used in a variety of portable electronic devices due to their high specific density and long cycle life.In recent years,the applications of lithium-ion batteries have been more and more widely,including in the fields of electric vehicles?EV?,hybrid vehicles?HEV?and grid-scale energy storage etc.So,the exploration of high performance cathode materials is critical for the commercialization of the lithium-ion battery in these fields.Among the available cathode materials,Li-rich layer oxide xLi2MnO3·?1-x?LiMO2?M = Mn,Ni,Co…?,have received intensive attention due to their higher specific capacities?>250 mAh g-1?,wide operating potentials?4.8-2.0V?,high thermal stability,low cost,et al.Despite the above attractive advantages,this material still remain substantial issues,for instance,the large irreversible capacity loss during the first cycle,poor rate and cycling performance,which tremendously restrict its practical applications.In this paper,we focused on the property modification of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode material,the main obtained results are listed as below:?1?The micro-sized precursor material(Mn_0.54Ni_0.13Co_0.13)?OH?₂ was synthesized by homogeneous co-precipitation method,the precursor was mixed with an appropriate amount of Li2CO3 and then sintered at high temperature to obtain Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ lithium-rich cathode material.The surface modification with AlF3 was carried out to improve the electrical performance of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂.The results show that during the AlF3 modification process,The Al³⁺ and F-are simultaneously doped into the crystal structure of the lithium-rich material,and this situation results in the increased cell volume,which facilitates the diffusion of lithium ions in the interior of the material.At the same time,LiF coating layer was formed on the surface of the cathode material,on the one hand,the presence of the coating layer can alleviate the lithium-rich cathode material from corrosion by acid species that originate from the decomposition of the organic electrolyte during the cycle process,on the other hand,the formation of the SEI layer is effectively suppressed by the Li F coating layer,which greatly facilitates the diffusion of lithium ions on the surface of the electrode material.?2?The nano-sized lithium-rich cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ was synthesized by spray drying method.The influences of surface modification process with Polydopamine on the structure and electrochemical performance of the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ were evaluated.The results demonstrated that: During the modification process,the surface of the cathode material was reduced to form a spinel coating layer,at the same time,the polydopamine was carbonized as a coating layer on the surface about 10 nm.The newly formed spinel coating layer possesses a three-dimensional lithium ion diffusion channel and greatly facilitates the diffusion process of lithium ions on the surface of the cathode material.In addition,not only the carbon coating layer is beneficial to improve the electronic conductivity,but also to alleviate the side effects between the electrolyte and the electrode material,and improve the structural stability of the cathode material.