| Supercapacitor is an energy storage device between lithium ion battery and traditional capacitor.It has the advantages of long cycle life,high power density and environmental friendliness.It has broad application prospects in new energy technology and electric vehicle field.Electrode materials are critical to the performance of supercapacitors,so a great deal of research effort is devoted to designing advanced electrodes.Graphene is a promising supercapacitor electrode material due to its unique structure and excellent physical and chemical properties.The oxygen functional groups,nanopores and their edge structures on the surface of graphene have important effects on their electrochemical properties,but the specific mechanism of influence is still unclear,and the extremely low bulk density of graphene hinders its application.Therefore,this paper studies the influence of the defect structure on the surface of graphene on the electrochemical properties.Simultaneously,by regulating the edge defects of graphene,a new method for preparing high density graphene electrode materials with defects is proposed,which effectively improves the volumetric energy density of graphene.The main research contents and results are as follows:1.Firstly,graphene materials G-200,G-400 and G-800 with different structural parameters were prepared by annealing graphene oxide at different temperatures?200°C,400°C,800°C?.The effects of parameters such as defect type,quantity and specific surface area on electrochemical performance were systematically studied.The results show that the content and type of oxygen functional groups are important factors affecting the electrochemical performance of graphene supercapacitors.As the annealing temperature increases,the oxygen functional groups of graphene materials decrease,and the specific capacitances of the material also decrease,the specific capacitances of G-200,G-400 and G-800 are 203,155 and 35 F g-1,respectively.In addition,oxidation and pore-forming treatment of graphene G-800 annealed at 800°C were also performed.After oxidation treatment,the specific capacitance of G-800 can be increased to 139 F g-1,but its specific capacitance is only 38 F g-1after pore-forming treatment.The above results indicate that the oxygen functional group plays an important role in the electrochemical performance of the graphene supercapacitor.2.A novel strategy for preparing high density graphene with rich defects for high-performance supercapacitors was proposed.Utilizing the evaporation self-assembly characteristic of graphene oxide,a graphene oxide film was prepared by blade-coating method,and then thermally reduced to a graphene film,and the graphene film was shredded into small flakes to prepare high density graphene.The shredded process interrupts the continuity of the graphene film and maintains its dense structure.The reduction of the size of the graphene sheet increases the boundary defects,and can simultaneously achieve high bulk density and rapid electron and ion transport.High density graphene exhibits high gravimetric capacitance(237 F g-1)and volumetric capacitance(261 F cm-3),as well as excellent cycle stability and capacity retention rate after 10000 cycles is98%.Moreover,the symmetrical supercapacitor using high density graphene as the electrode materials can obtain energy density of up to 16 Wh L-1 at a power density of 88 W L-1 in the aqueous system.This strategy provides a new way to design high volumetric energy density supercapacitors for energy storage applications in the future. |
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