Design,Preparation And Asymmetric Supercapacitor Performances Research Of Carbon Nanofiber Composite Electrodes

With the development of high-performance practical energy storage devices,supercapacitors with high power density,fast charging/discharging process and long service life have attracted much attention in the field of energy storage.However,the low energy density limits the wide application of supercapacitors.In this paper,the carbon nanofiber-based binder-free electrode materials were constructed and systematically characterized and the properties of materials are improved by optimizing the preparation process and modification measures.Firstly,Fe₂O₃@carbon nanofiber composite electrode was constructed by using Fe Cl₃ as the iron source,carbon nanofiber cloth as the support,and graphene as the carbon source through hydrothermal reaction and heat treatment.The effect of Iron concentration on morphology,structure and electrochemical performance were systematically studied.Finally,the optimal concentration process parameters were determined.After that,Fe OOH@CNFs was coated with graphene by a simple and efficient coating method,and the influence of oven drying and freeze-drying coating methods on morphology,structure,specific and electrochemical properties were investigated.The graphene protective layer can improve the electrical conductivity of the active material,alleviate the volume expansion and contraction of the electrode material during the process of charging and discharging.Thereby ensuring its high specific capacity and excellent cyclic stability.It was found that Fe₂O₃@CNFs-r GO-f(freeze-drying coating)has ideal graphene protective layer,good porous structure and high conductivity,thus exhibiting a superior electrochemical performance:a large potential range of 1.2 V,an ultrahigh specific capacitance of 488 F g^-1at a current density of 2 A g^-1 and excellent rate capability(194 F g^-1at 20 A g^-1).Finally,in order to construct asymmetric supercapacitors,the cathode materials are studied.Ni-Co LDH@carbon nanofibers with graphene coating(Ni-Co LDH@CNFs-r GO)composites as a binder-free positive electrode of supercapacitors were prepared by hydrothermal reaction method.The ultrathin layered structure of Ni-Co LDH nanosheets promotes the fast electrochemical reactions and increases the utilization of active electrode materials.The composite material exhibits a high specific capacity of 932 F g^-1 at 2 A g^-1 in a three-electrode system and excellent rate capability of 366 F g^-1at 20 A g^-1.Asymmetric supercapacitors were constructed using Ni-Co LDH@CNFs-r GO-5 and Fe₂O₃@CNFs-r GO-f as the positive and negative electrode,respectively.In the asymmetric system,it exhibits a high specific capacity of 144 F g^-1at 2 A g^-1 and excellent rate performance.The prepared asymmetric device shows an energy density of 45 W h kg^-1 at power density of 1528 W kg^-1.The preparation method of electrode materials proposed in this paper effectively improves the electrochemical performance of carbon nanofiber composite,and provides a new idea for the preparation of high-performance carbon based materials.