Preparation And Modification Of Manganese Ferrite As Anode Material For Lithium-ion Batteries

Energy shortage and excessive use of fossil energy lead to serious environmental pollution,which drives people to seek cleaner and green renewable energy.The use of renewable energy requires advanced and efficient energy storage and conversion devices.However,as a widely used energy storage and conversion device,the energy density of lithium-ion batteries using graphite as an anode material has been unable to meet people’s increasing demand.Therefore,it is urgent to develop anode materials with higher energy density for lithium-ion batteries.Cubic spinel-type manganese ferrite（Mn Fe₂O₄）,as an anode material for lithium-ion batteries,has been widely studied for its high theoretical specific capacity,environmental friendliness and abundant natural resources.However,Mn Fe₂O₄undergoes large volume changes when lithium ions are intercalation and deintercalation,resulting in agglomeration and pulverization,and its inherent low conductivity hinders its application in lithium ion batteries anode material.In order to improve these problems,this paper takes manganese ferrite（Mn Fe₂O₄）as the research object,through the design and synthesis of nanostructured materials,the formation of complexes with carbon materials and ion doping to modify the materials to improve the electrochemical performance of the materials,the nanostructure,composition,electrochemical performance and lithium storage mechanism of the modified materials are studied.The specific research contents and results are as follows:By adding ammonium fluoride as a fluorine source and using a solvothermal method to synthesize fluorine-doped Mn Fe₂O₄ nanorods,the rod-shaped material has a higher specific surface area,so it can provide shorter ion and electron diffusion channels and more lithium storage sites.Under high temperature hydrothermal environment conditions,ammonium fluoride decomposes into hydrogen fluoride and ammonia gas,fluorine ions remain in the material.Fluorine doping can effectively reduce the resistance of the Mn Fe₂O₄ material and suppress the crystal lattice distortion of the material during the charge-discharge cycling,and thus significantly improve the cycling stability and rate performance of Mn Fe₂O₄ materials.Using glucose as a carbon source,carbon-coated fluorine-doped Mn Fe₂O₄ nanocomposites are synthesized through secondary hydrothermal and subsequent high-temperature calcination.The carbon coating layer can be used as a fast diffusion channel for ions and electrons and a physical buffer layer during lithium insertion and extraction,effectively improving the electrochemical performance of the Mn Fe₂O₄ material.Under the current density of 200 m A/g,the initial discharge and charge specific capacity of the synthesized material are 1372 m Ah/g and 932 m Ah/g respectively,and the initial coulombic efficiency is as high as 68%.The reversible discharge specific capacity is 900 m Ah/g after 150 cycles,and the capacity retention can reach 94%.And the material exhibits superior rate performance,with specific discharge capacities of 710,621,484,344,and 201 m Ah/g at current densities of 200,500,1000,2000,and 3000 m A/g,respectively.