Preparation And Electrochemical Performances Of Fe₃O₄/C Composite Anode Materials For Lithium Ion Batteries

As a crucial part of LIBs,the commercial graphite anode has an inherent shortage of capacity(372 mAh g^-1),which is inadequate to meet the growing requirements of high energy batteries.Therefore,to develop the alternative anode materials with high energy density is imperative.Among transition metal oxides,magnetic oxide（Fe₃O₄）have attracted tremendous attention as anode materials for lithium ion batteries,owing to its high theoretical capacities,stable physical and chemical properties,eco-friendliness and nature abundance.However,the electrode shows poor rate and cycling performance,because of poor conductivity and pulverization resulted from severe volume expansion during cycling.Hence,appropriate measures should be taken to solve these problems.In this paper,the basic properties of Fe₃O₄ and its electrochemical lithium storage mechanism were reviewed summarized firstly.Then,the current research progress and latest research direction of Fe₃O₄ was summarized.Based on the research of the related literatures,to explore new methods with simple operation and green pollution-free synthesis Fe₃O₄/C composite materials,which has good cycle stability,ratio performance.Moreover,the surface morphology,microstructure and chemical composition of the as-prepared composite were examined in detail through XRD,SEM,TEM,TGA,XPS,N₂ adsorption/desorption methods.The electrochemical performances of the composites were thoroughly studied.The contents are as following:（1）A new composite with Fe₃O₄ and Cu（²0 nm）nanoparticles encapsulated in carbon nanofibers（CNFs）is fabricated through a simple electrospinning technique followed by heat treatment.In synthetic progress,the PVP/Fe（NO₃）₃/Cu（CH₃COO）₂percursor fibers prepared via a simple electrospinning technique will change to Fe₃O₄/Cu/CNFs by controlling calcination temperature and time.The one-dimensional CNFs not only can show good stability as a support,but also act as high-efficient transport pathways for ions and electrons.Cu nanocrystals in the CNFs ensures the composite a good conductivity.As a result,the as prepared Fe₃O₄/Cu/CNFs composite displays an outstanding cycle performance with a reversible capacity of 540 mAh g^-1 after 100 cycles at100 mA g^-1,as well as a good rate capability of 331 mAh g^-1 after 100 cycles at 1 A g^-1.（2）A novel sponge type Fe₃O₄/C composite is prepared by a sol-gel type method and subsequent heat-treatment process with sodium alginate as the carbon source and ferric nitrate as the iron source.The sponge structure Fe₃O₄/C composite possesses abundant porous structure,in which highly dispersed Fe₃O₄ nanocrystals were encapsulated in the carbon matrix.In this architecture,the 3D porous network property ensures electrolyte sufficient accessibility,meanwhile,nanosized Fe₃O₄ can inproves the structure stability.As a result,this composite electrode shows excellent cycling stability and superior rate performance.It exhibits a high reversible capacity of 540.5 mAhg^-1 after 100 cycles at 100mA g^-1.When current density increased to 1 and 2 Ag^-1,the composite displays 482 and415 mAhg^-1,respectively.（3）A uniform Fe₃O₄@C nanospere composite with was successfully synthesized by one-pot hydrothermal method and Fe₂O₃@C precursor followed by a post-calcination treatment,taking use of PVP as carbon precursor and ferric nitrate as iron source.The use of NaCl has a direct effect on the nanospere structure formation of Fe₃O₄@C composite.The nanosized Fe₃O₄ nanocrystals coated by conductive carbon not only provides a short diffusion length for lithium ion transport,but also effectively circumvent the volume expansion/contraction associated with lithium insertion/extraction.When directly studied as anode for LIBs,Fe₃O₄@C composite electrode exhibits a reversible capacity of 695 mAh g^-1 after 100 cycles at 100 mA g^-1.When current density increased to1 Ag^-1,the composite displays 548mAhg^-1。...