Synthesis And Lithium-storage Performance Of Fe-based Oxides/Graphene Nanocomposites

Lithium-ion batteries have been widely applied in portable consumer electronics,electric vehicles and hybrid vehicles,renewable energy and so on.However,the current commercial graphite anode suffers from a low theoretical capacity(372 mA h g^-1),which is insufficient to meet the market demand.Therefore,it's urgent to exploit alternative anode materials with large capacity and long cycling life.Fe-based oxide anodes based on conversion mechanism exhibit the advantage of high theoretical capacity,low cost,and environmental benignity,indicating great promise as anode materials.In this paper,Fe-based oxides/graphene nanocomposites were investigated by constructing reasonable composite structure and adjusting compositions to improve the lithium storage performance.?1?Graphene-wrapped mesoporous Fe₂O₃ nanoparticles has been constructed through a self-assembled process.The introduced graphene oxidation?GO?transforms Fe₃O₄ with nonuniform morphology and size into mesoporous Fe₂O₃ with uniform morphology and size.The volume change and agglomeration of Fe₂O₃ are effectively inhibited due to the wrapped structure of Fe₂O₃/graphene nanocomposite;meanwhile,the mesoporous structure of Fe₂O₃ nanoparticles shortens the transport distances of lithium ions and electrons,enhances the contact area between the electrode and electrolyte,and also provides extra space to accommodate the volume change during cycling processes.Benefiting from this rational architecture,Fe₂O₃/graphene electrode delivers a large reversible capacity of 1098 mA h g^-1 at1000 mA g^-1 after 500 cycles,exhibiting excellent electrochemical performance and great promise as anode for lithium ion batteries.?2?A facile and direct strategy is developed to prepare Fe₃O₄/graphene nanocomposites by annealing GO-Fe precursor.The controlled morphology and size of Fe₃O₄ nanoparticles anchored on graphene are achieved by adjusting the annealing temperature.The sample with small-size Fe₃O₄ nanoparticles exhibits preferable reversible capacity of 1060 mA h g^-1 at 100 mA g^-1 after 100 cycles.This is related to Fe₃O₄ nanoparticles with small size,which provides more lithium storage sites,shorten the transport distances of lithium ions and electrons,and effectively buffers the volume changes during cycling processes compared with large-size ones.?3?N₂H₄·H₂O-assisted synthesis strategy is adopted to inhibit the oxidation of Mn²⁺ions under alkaline aqueous solution,thus providing a viable solution to hydrothermal synthesis of MnFe₂O₄/graphene nanocomposite.More importantly,the resultant MnFe₂O₄ nanoparticles with small size of 5-30 nm are homogeneously anchored on graphene.Electrochemical measurements reveal that MnFe₂O₄/graphene electrode displays large reversible capacity and cycling stability with 773 mA h g^-1 at1000 m A g^-1 after 210 cycles.?4?CoFe₂O₄ nanocube/graphene nanocomposite has been synthesized via a hydrothermal strategy.The formed CoFe₂O₄ nanocubes depend on the synergy effect of GO and N₂H₄·H₂O during the synthesis process.More importantly,the intimate interfacial contact between nanocubic CoFe₂O₄ and graphene promotes the dispersion of CoFe₂O₄ nanocubes on graphene and facilitates fast transport of lithium ions and electrons through the interface.Thus,the structure stability and electrochemical kinetics of electrode are improved.When served as anode material,this electrode demonstrates a large reversible capacity of 835 mA h g^-1 at 1000 m A g^-1 after 200cycles.?5?Zn_0.25Co_0.75Fe₂O₄ nanocube/graphene nanocomposite has been developed through Zn doping on the basis of CoFe₂O₄ nanocube/graphene nanocomposite.Zn_0.25Co_0.75Fe₂O₄ completely inherits the nanocubic morphology;meanwhile,Zn doping further improves the electron and lithium ion transport of electrode.As a result,the prepared electrode displays a large reversible capacity of 1029 mA h g^-1 at 1000m A g^-1 after 200 cycles.