Construction Of Niobium Pentaoxide/reduced Graphene Oxide Composite Fiber And Applicaiton Of Flexible Sodium Ion Capacitor

Flexible energy storage equipment has attracted extensive attention from researchers because of its great development potential.Therefore,the development of flexible energy storage equipment with high capacity,high stability and good safety is the main development direction at present.Sodium ion capacitors(NIC)have the advantages of both supercapacitors and metal ion batteries,and sodium is abundant and low in cost.Therefore,NIC is expected to be an ideal energy storage device.However,in NIC,high speed adsorption/desorption reaction occurs in the active carbon usually used as the positive electrode,so the high reaction rate of the negative electrode material is required to match it.Niobium pentaoxide(Nb₂O₅)is a kind of intercalated pseudocapacitive material with high reaction rate,but its low conductivity greatly limits its electrochemical performance.In this paper,the carbon coating of niobium pentaoxide(T-Nb₂O₅)and the composite with reduced graphene oxide(rGO)were carried out.The prepared T-Nb₂O₅ composite was filled into the rGO skeleton to form the self-supporting fiber by restricted hydrothermal freeze-drying molding.The electrochemical properties of the T-Nb₂O₅ composite were studied as the flexible anode material of NIC.The main research work and results are as follows:(1)Investigation on the molding and electrochemical properties of niobium pentaoxide/reduced graphene oxide composite fiber:T-Nb₂O₅ nanoparticles were prepared by solvothermal combined calcination and mixed with GO.T-Nb₂O₅/rGO composite fibers with different structures were prepared by wet spinning drying and restricted hydrothermal freeze-drying,respectively and by hydrazine hydrate steam reduction.Electrochemical results show that the capacities of W-T-Nb₂O₅/rGO and C-T-Nb₂O₅/rGO fibers are 59 m Ah/g and 85 m Ah/g,respectively,after 100 charge and discharge cycles at current density of 0.1 A/g.In conclusion,compared with the fibers prepared by wet spinning drying,the fibers prepared by restricted hydrothermal freeze-drying have better electrochemical properties.(2)Restricted hydrothermal freeze-drying of niobium pentaoxide composite carbon material/reduced graphene oxide fiber and its electrochemical properties:The rGO composite T-Nb₂O₅(T-Nb₂O₅-rGO)and carbon-coated T-Nb₂O₅(T-Nb₂O₅-C)were prepared by solvent-heating and calcination of Niobium chloride(Nb Cl₅)mixed with GO and glucose respectively.T-Nb₂O₅-rGO/rGO and T-Nb₂O₅-C/rGO composite fibers with porous structure were prepared by the restricted hydrothermal freeze-drying process described in the previous chapter.The electrochemical properties showed that the discharge capacities of T-Nb₂O₅-rGO/rGO and T-Nb₂O₅-C/rGO fibers were 125 m Ah/g and 120 m Ah/g,respectively.Compared with the capacity(85 m Ah/g)of C-T-Nb₂O₅/rGO fiber prepared by the direct combination of T-Nb₂O₅ and GO in the previous chapter,the electrochemical performance is significantly improved.(3)Preparation of carbon-coated niobium pentaoxide composite reduction graphene oxide/rGO fiber and its flexible sodium ion capacitor performance:In order to further improve the electrochemical performance,T-Nb₂O₅-C-rGO/rGO composite fiber was prepared by carbon coating and rGO composite of T-Nb₂O₅-C-rGO.Then,T-Nb₂O₅-C-rGO/rGO composite fiber was filled into the rGO skeleton by limited hydrothermal freeze-drying,and the porous structure T-Nb₂O₅-C-rGO/rGO composite fiber was constructed.Electrochemical tests of the button cell showed the fiber capacity of 182 m Ah/g after 100 charge and discharge cycles at current density of0.1 A/g.The flexible sodium ion capacitor is assembled by T-Nb₂O₅-C-rGO/rGO fiber as the negative electrode and activated carbon/rGO(AC/rGO)fiber as the positive electrode,which not only had good energy density(40 Wh/kg)and power density(436 W/kg),but also has a capacity retention rate of 70%after 2000 charge discharge cycles at current density of 1 A/g.The composite fiber with porous structure provides a kind of high performance anode material for flexible sodium ion capacitors.