Research On Preparation And Properties Of Carbon Material/iron Oxide Composites For Supercapacitors

Supercapacitor is a new type of energy storage devices,with attractive properties including high power density,long cycle life,safety,reliability and no pollution.Electrode material is an important part for supercapacitor,playing a decisive role for the electrochemical performance of supercapacitor.Iron oxide is an ideal anode material for supercapacitor.However,using pure iron oxide as electrode material of supercapacitor has some disadvantages,such as poor electrical conductivity and poor cycle stability and so on.In this thesis,we studied the synthesis of iron oxide composites with graphene and carbon nanotubes for high performance by simple method.The main contents are as follows:(1)The graphene/iron oxide composites were prepared by chemical bath method under constant temperature.The effect of the Fe Cl2 ratio and the reaction temperature on the electrochemical properties of graphene/iron oxide composites as supercapacitor was studied in this paper.The results show that the graphene/iron oxide composites prepared with 100 mg Fe Cl2 and 90°C reaction temperature exhibits the best supercapacitor performance.Specific capacitance of 727F/g could be delivered at a current density of 2A/g.The capacitance could remain 31.69% after 5000 charging and discharging cycles at a current density of 4A/g.(2)The carbon nanotubes/iron oxide composites were also prepared by chemical bath method under constant temperature.The effect of the Fe Cl2,the reaction temperature,magnetic stirring speed and reaction time on the microstructures and properties of carbon nanotubes/iron oxide composites was studied.The results show that the carbon nanotubes/iron oxide composite prepared with 100 mg Fe Cl2,90°C reaction temperature,300 r/min magnetic stirring speed and 2h reaction time exhibits the best supercapacitor performance.The specific capacitance 942F/g could be delivered at a current density of 2A/g,and 645F/g could be remained at a current density of 15A/g,indicating a good rate performance.The capacitance retention is 15.5% after 5000 charging and discharging cycles at a current density of 4A/g.Heat treatment could improve cycling and rate performance of composite due to the enhancement of the contact force between the iron oxide nanoparticles and the carbon nanotubes.However,heat treatment of the carbon nanotubes/iron oxide composite would induce the aggregation of iron oxide nanoparticles,resulting in the increased size of iron oxide nanoparticles and the reduced initial specific capacitance at low current densities.