Study On Preparation And Electrochemical Properties Of Magnetic Oxide@C As Anode For Lithium Ion Batteries

Among transition metal oxides, magnetic oxide (Fe3O4) have attracted tremendousattention as anode materials for lithium ion batteries owing to its high theoreticalcapacities, stable physical and chemical properties, eco-friendliness and nature abundance.However, the electrode shows poor rate and cycling performance because of mechanicaldegradation and pulverization resulted from severe volume expansion during cycling.Hence, appropriate measures should be taken to solve these problems. In previousresearches, two main kinds of strategies have been generally considered:(1) preparation ofnanosized particle to offer a shorter diffusion length for lithium ion (2) surfacemodification or geometric confinement for goal particle. These two parts have beenadopted together to improve electrochemical performance of magnetic oxide electrodemarkedly. In order to prepare for composites for lithium storage with enhancedelectrochemical performance, in this paper N-rich carbon coated Fe3O4(Fe3O4@CN)composites, Fe3O4/grapheme and Fe3O4nanoparticles embedding in carbon crystal latticecomposites (Fe3O4@C) were synthesized by three methods, and characterized by XRD、SEM、TEM、XPS、Raman、FTIR. The electrochemical properties were researched bygalvanostatic charge-discharge cycling and electrochemical impedance spectra.In this article, we introduce a solvothermal method combined with a facile surfactantdirected chemical polymerization method to prepare highly-regulated Fe3O4@polypyrrolecore-shell microspheres, then Fe3O4@PPy composites were thermally treated to synthesizepeanut-like Fe3O4@CN core-shell microspheres. Fe3O4was fabricated by a facilesolvothermal reaction using FeCl3·6H2O and CH3COONa·3H2O as raw materials andethylene glycol as solvent and reducing agent. The product shows high purity, goodcrystallinity and uniform particle distribution. The effects of solvent and the rato ofreagents on the crystal structure, morphologies and electrochemical performance of Fe3O4have been analyzed. It was found that in our experiment condition Fe3O4synthesized at180℃for8h shows best electrochemical performances using n(NaAc·3H2O):n(FeCl3·6H2O)=8dissolved in ethylene glycol. In the process of chemical polymerization and thermal treatment, the effect of FeCl3·6H2O addition, pyrrole addition and temperatureon the morphologies and electrochemical performance of Fe3O4@CN composites werediscussed. The results demonstrate that FeCl3·6H2O addition and pyrrole additioninfluence the condition of carbon coating, and temperature influences the carboniazationand nitrogen content. Fe3O4@CN composite treated at600℃for3h with4.7gFeCl3·6H2O and1.5g pyrrole shows the best performance. The charge specific capacity ofthe Fe3O4@CN composite is670mAh g-1after30cycles at a current density of92.6mAg-1.Fe3O4/GNS composites were successfully prepared by solvothermal process. Theresults of SEM and TEM shown Fe3O4nanoparticle (5-20nm) compounded in thegraphene. The charge capacity of the Fe3O4/GNS composite is about400mAh g-1after30cycles at a current density of92.6mA g-1.Besides, Fe3O4@C composites were synthesized by template method. The resultsshoen that Fe3O4@C using NaCl as template shows the best performance. The chargecapacity of the Fe3O4/GNS composite is about760mAh g-1after30cycles at a currentdensity of92.6mA g-1with good rate performance.