Preparation And Study On Lithium Storage Properties Of Iron Oxide/3D Graphene Composites

With the rapid development of portable electronic devices and electric vehicles industry,lithium ion batteries with higher energy and power density,better cycling stability and safety are in great demand.Anode materials as one of the important factors to improve the performance of lithium ion batteries,have attracted extensive research by many researchers at home and abroad.Iron oxides have attracted tremendous attention owing to its high theoretical capacity(926 mAh g^-1 of Fe₃O₄,1007 mAh g^-1 of Fe₂O₃),natural abundance,low-cost and environmental friendliness.However,iron oxides suffer from poor electronic conductivity and severe volume change in charging and discharging,which seriously affects the cycling stability and the rate performance of lithium ion batteries.In this paper,N-doped 3D porous graphene encapsulated FeO_x spheres composites?FeO_x@N-3DG?and carbon and graphene double-shell confined hollow Fe₃O₄ spheres composites?Fe₃O₄@N-C@rGO?with excellent electrochemical properties were prepared by simple methods with reasonable design of structure.Hierarchical porous FeO_x@N-3DG composites were prepared by a simple hydrothermally assisted in-situ electrostatic self-assembly method and thermal treatment.The different ratio of reactants and hydrothermal reaction time were investigated for the structure formation and the electrochemical properties of FeO_x@N-3DG composites.And the results show that the as-prepared FeO_x@N-3DG composites that the mass ratio of precursor FeOOH and GO is 1:1 and the hydrothermal reaction time is12 h exhibite best structure and electrochemical performance for lithium storage.The specific capacity of FeO_x@N-3DG is as high as 1102 mAh g^-1 at the current density of 0.1 A g^-1 and the specific capacity of 753 mAh g^-1 remains with the capacity retention rate of 81.6%after1000 cycles at 1 A g^-1Hollow Fe₃O₄ nanospheres composed of many particles about 10 nm were prepared by a hydrothermal method,and then carbon and graphene double-shell confined hollow Fe₃O₄ spheres composites were obtained by dopamine polymerization coating and electrostatic attraction coating of graphene.Besides,the effect of graphene encapsulation and carbon-coating on improving the electrochemical performance of hollow Fe₃O₄nanospheres was explored by contrastive analysis.Carbon-coating improves the structure and electrochemical stability of hollow Fe₃O₄ nanospheres.The tight coating of rGO also limits the structure change of Fe₃O₄@N-C in some way and the interconnected rGO layer structure provides a continuous conductive network for the whole electrode,which promotes the reaction kinetics and improves the electrochemical properties of the composite materials.Fe₃O₄@N-C@rGO electrode delivers high reversible specific capacity of 986.2 mAh g^-1 at the current density of 0.1 A g^-1;the specific capacity is up to947.7 mAh g^-1 at 0.5 A g^-1 after 300 cycles;the specific capacity can still be maintained at503.7 mAh g^-1 after 500 cycles under the current density of 1 A g^-1.