Preparation Of Fe₃O₄/Graphene Namocomposites And Its Application To Lithium-ion Batteries

Lithium-ion battery (LIBs) has become most widely used, and mostpromising, one of the most studied by people currently. Metal oxide,because of its low operating potential and high lithium storagecapacity,was widely studied as LIBs anode material. Fe3O4has beenwidely investigated as one of the metal oxide due to its hightheoretical capacity (924mAh g-1), high electrical conductivity, lowcost, eco-friendliness. However, its practical application in LIBs islimited by the volume change in the process of charging anddischarging that leads to poor cycling performance. Graphene hasdrawn tremendous interest duo to its high thermal conductivity, highmechanical properties, good electronic conductivity and largesurface area. It was used as LIBs anode materials research, showinghige reversible specific capacity, but the initial coulombic efficiencyis low and rapid capacity fading. This paper mainly through thepreparation of Fe3O4/graphene nanocomposites solved the aboveproblems.(1) Graphite Oxide were prepared via improved Hummers method.And was exfoliated to obtained graphene oxide colloid by means ofultrasonic treatmenf. Following, graphene was prepared by chemicalreduction with Trisodium citrate dehydrate. And compare the each stage of product structure and form using XRD, FT-IR, UV, SEM, TEMobservation. Results show that the graphite was oxided as graphiteoxide, Trisodium citrate dehydrate reduced graphite oxide intographene nano film successfully, but layer is thicker, which isexpected to be further improved. Then using coprecipitation withFeCl3and FeCl24H2O, NaOH solution, reflux preparing Fe3O4nanoparticles. And Fe3O4nanoparticles was characterized throughXRD, FT-IR, SEM, TEM, the results show that the success of preparedFe3O4nanoparticles whose size about10nm.(2) Three different ratios of Fe3O4/graphene nanocomposites wassynthesized using coprecipitation in graphene oxide colloidal, andcalculate the mass ratio of each composite material. Thencharacterize Fe3O4/graphene nanocomposites by XRD, FT-IR, SEM,TEM, the results show that in the composite material, Fe3O4nanoparticles dispersed on the surface of graphene in the form ofsphere like morphology, these particles size ranges from severalnanometers to dozens of nanometer. Finally the Fe3O4/graphenenanocomposite and pure Fe3O4nanoparticles were assembled intoLIBs, galvanostatic charge-discharge measurements shows thatFe3O4nanoparticles, Fe3O4/G1, Fe3O4/G2, Fe3O4/G3dischargingspecific capacity for the first time are separately641.3mAh g-1,623mAh g-1,641mAh g-1,679mAh g-1at the voltage range of0.01-3.0V, current density of100mA g-1.After20cycles, the reversiblespecific capacity is92mAh g-1243mAh g-1,301mAh g-1,465mAh g-1,; Coulomb efficiency is72.8%,79.9%,79.4%,81.3%. The resultsshow that assembled cells with the Fe3O4/graphene nanocompositeswhose cycle performance is more superior than that with pure Fe3O4 nanoparticles, and the reversibility and cycle performance of Fe3O4/G3(including44%Fe3O4nanoparticles) is best. AC impedance testresults show that the Fe3O4nanoparticles, Fe3O4/G1, Fe3O4/G2,Fe3O4/G3, solid electrolyte film (SEI) and charge transfer resistancereduced, lithium ion diffusion degree increased, reaction kinetics ofthe battery was getting better and better in turn.(3) In the presence of H2C2O4in graphene oxide colloid, reduce thegraphene oxide with Fe. By XRD, FT-IR, SEM, we find graphene nanofilm and Fe3O4/graphene--Fe composite material are obtainedsimultaneously; FeC2O4H2O is added to graphene oxide colloid,obtained Fe3O4/graphene composites.(4) Fe3O4/graphene-Fe composite materials and Fe3O4/graphenecomposites as working electrode were assembled into LIBsrespectively, in the voltage range of0.01-3.0V, current density of100mA g-1, the first discharging specific capacity of LIBs were801.7mAh g-1,718.7mAh g-1; Coulomb efficiency is69.4%,63.3%respectively.After20cycles, discharge specific capacity were398.5mAh g-1,312mAh g-1, reversible capacity retention rate were49.7%,43.4%. ACimpedance show that,by contrast, solid electrolyte film (SEI) andcharge transfer resistance is small for the Fe3O4/graphene-Fecomposite, while lithium ion diffusion degree of Fe3O4/graphenecomposites is higher.