Preparation Of High-performance Graphene-based Fibrous Supercapacitors And Investigation Of The Mechanism Of Performance Enhancement

Flexible fibrous supercapacitors are a novel type of flexible energy storage apparatus whose performance is mainly influenced by the electrode materials.Among the common electrode materials,graphene-based materials have attracted much attention due to their high theoretical physical and mechanical properties and electrochemical performance.However,the actual specific surface area of pure graphene fibers is low and there are many defects inside the fibers,resulting in low specific capacitance and conductivity of graphene fibers,and the actual electrochemical properties or mechanical properties need to be improved.The common methods to enhance the electrochemical performance of graphene electrodes are mainly divided into the structural design of the fiber interior and the structural design of the fiber surface.For the internal structural design of fibers,this paper designs a new carbon nanotube/MXene/graphene composite fiber with a three-dimensional bonded cross-linked network structure using graphene as the substrate and MXene and carbon nanotubes as the reinforcement,which improves the mechanical properties of fibers while enhancing the electrochemical properties of fibers.For the design of the fiber surface structure,this paper uses graphene fiber as the substrate,and introduces a porous structure on the fiber surface while constructing a conductive structure coating,thus enhancing the fiber conductivity while improving the fiber specific surface area,which makes the obtained graphene-based fiber electrode have good electrochemical properties.The details of all experiments are as follows:1.Novel carbon nanotube/MXene/graphene composite fibers were prepared by a simple wet spinning method using MXene,carbon nanotubes and graphene oxide as raw materials.By comparing its mechanical properties,electrical conductivity and electrochemical properties with MXene/graphene composite fiber and carbon nanotube/graphene composite fiber,the carbon nanotube/MXene/graphene composite fiber has the maximum tensile strength of 147.07 MPa,the maximum electrical conductivity of 420.42 S·cm^-1 and the maximum area specific capacitance of237.00 m F·cm^-2,which proves The superiority of the carbon nanotube/MXene/graphene composite fiber structure in simultaneously enhancing the mechanical properties and electrochemical properties of the electrode was demonstrated.2.By further analyzing and characterizing the fiber structure,a three-dimensional cross-linked bonding network structural model of carbon nanotube/MXene/graphene composite fibers was proposed to further elucidate the mechanism of MXene and carbon nanotubes synergistically enhancing graphene fiber electrodes.In addition,to investigate the influence of the components within the fiber on this structure,carbon nanotube/MXene/graphene composite fibers with different carbon nanotube contents were prepared and the comparative structural analysis of the properties was performed by changing the ratios of carbon nanotubes and MXene to graphene.When the mass ratio of CNT and MXene/graphene is 1:20,the fiber has the best fiber structure and thus the best combined mechanical and electrochemical properties.Therefore,the supercapacitor assembled with this fiber as electrode has the highest energy density of 5.27μW·h·cm^-2 and good cycling performance（95.60%capacitance retention after 8000charge/discharge cycles）.However,when the mass ratio of CNT and MXene/graphene was 1:10,the fiber had the worst mechanical properties（tensile strength of 81.80 MPa）and capacitance retention of 40.85%due to the agglomeration of CNT that destroyed the internal structure of the fiber.3.Polypyrrole-coated porous graphene fibers were prepared by using graphene fibers prepared by wet spinning as a substrate with high-temperature activation and polypyrrole oxide coating.Due to the high specific surface area and electrical conductivity of 128.25 S·cm^-1,the fibers show the highest area specific capacitance of 31.25 m F·cm^-2,which is 4.81 times higher than that of pure graphene fibers(6.50 m F·cm^-2),reflecting the superiority of polypyrrole-coated porous graphene fibers in terms of structure and performance.