Synthesis And Performance Study Of Fe₃O₄ Coated With Carbon Via Polymerization Reaction As Anode Materials For Lithium-ion Batteries

Lithium-ion batteries play a great role in portable mobile electronic devices,new energy vehicles,energy storage power plants and other fields,but the low theoretical capacity of traditional graphite anode materials is a bottleneck in the development of lithium-ion batteries.Among the new anode materials,Fe₃O₄ is widely studied due to its own large theoretical capacity,but Fe₃O₄ anode materials have poor electrical conductivity and large volume changes during charging and discharging,so it is important to study the modification of Fe₃O₄ materials to improve their electrochemical properties.Compounding with carbon materials is a common means to modify Fe₃O₄materials,and Fe₃O₄ materials compounded with carbon materials have good electrical conductivity and can maintain their own structural stability during the charge/discharge process.In this research,Fe₃O₄ nanoparticles were firstly synthesized by co-precipitation method and solvent thermal reduction method,and their morphological and electrochemical properties were investigated.By comparison,the Fe₃O₄ nanoparticles synthesized by the solvothermal method were selected as precursors for carbon coating using phenolic condensation reaction,dopamine polymerization reaction and polyvinylpyrrolidone polymerization reaction,respectively,and the morphology,components and electrochemical properties of the composites were investigated.The Fe₃O₄(c-Fe₃O₄)nanoparticles synthesized using the co-precipitation method exhibit a pagoda or cone shape with a first discharge specific capacity of 950 mAh·g^-1at a current density of 0.5 A·g^-1 and 246 mAh·g^-1 after 300 cycles at a current density of 1 A·g^-1.The Fe₃O₄(r-Fe₃O₄)synthesized by the solvent thermal reduction method are nanospheres with diameters 280 nm-300 nm nanospheres,and the first discharge specific capacity is 961 mAh·g^-1 at 0.5 A·g^-1 current density and 309 mAh·g^-1 after 300cycles at 1 mAh·g^-1 current density.The carbon-coated Fe₃O₄ material was synthesized by the dopamine polymerization reaction using the Fe₃O₄ material synthesized by the solvent thermal reduction method as the precursor,and by the phenolic condensation reaction.In addition,the carbon-coated Fe₃O₄ materials were also synthesized by the one-step polyvinylpyrrolidone polymerization reaction.The carbon layer thickness of the carbon covered Fe₃O₄ composite(r-Fe₃O₄@C)prepared by phenolic condensation was about10 nm,and the first discharge capacity was 1248 mAh·g^-1 at 0.5 A·g^-1 current density,and the specific capacity was 404 mAh·g^-1 after 300 cycles at 1 A·g^-1 current density;the carbon covered Fe₃O₄ composite prepared by dopamine polymerization(r-Fe₃O₄composite material(r-Fe₃O₄@Cx Ny)with a thickness of about 20 nm,the first discharge capacity of 1480 mAh·g^-1 at 0.5 A·g^-1 current density and the specific capacity of 512 mAh·g^-1 after 300 cycles at 1 A·g^-1 current density;the carbon coated Fe₃O₄ composite material(Fe₃O₄@Cx Ny)prepared by polyvinylpyrrolidone.Cx Ny),the basic unit of which is a nanosphere with a diameter of about 350 nm and the diameter of Fe₃O₄ particles in the nanosphere is about 80 nm,has a first discharge capacity of 1387 mAh·g^-1 at a current density of 0.5 A·g^-1 and a specific capacity of 495mAh·g^-1 after 300 cycles at a current density of 1 A·g^-1.