| With the rapid development of flexible wearable electronic devices,it is urgent to develop a matching energy storage device.Because of its unique one-dimensional structure,fibrous energy storage devices are light in weight and can be woven,so it is very suitable to be combined with traditional textile technology and applied to the field of wearable electronic energy supply.The new graphene-like two-dimensional nano-sheet,MXene,has shown great development potential in the fields of conductive sensing fiber and energy storage fiber electrode.The key of pure spinning fiber forming technology lies in regulating the directional and orderly arrangement of MXene layers,constructing a complete ion transmission channel between nano-sheets,and balancing the contradiction between interlayer bonding and transition stacking of nano-sheets.Theoretically,the pure spinning structure has higher conductivity,but due to the harsh etching process,the actually prepared nanoplatelets have smaller and different sizes,which is not conducive to the construction of fiber grain boundaries.At present,the selection of suitable polymer materials for blending and spinning is more operable,and at the same time,the fiber-forming performance of the fiber is more designable.Therefore,the selection of suitable polymer materials and structural design are the key to prepare high-efficiency fiber electrodes.Therefore,in this paper,MXene nanosheets and polyacrylonitrile were selected as raw materials,and different fiber electrodes were prepared by wet spinning method,high-temperature carbonization treatment and grafting modification,by changing the fiber combination mode and fiber internal macro-micro structure design,and the electrochemical properties of fiber electrodes and supercapacitors were investigated.This study not only expands the application of metal carbide or nitride in fiber electrode,but also provides a new idea for the development of flexible energy storage materials.The specific research contents are as follows:Firstly,by preparing different concentrations of polyacrylonitrile spinning solution,the spinnability of polyacrylonitrile material and the structure and performance characteristics of the constructed fiber were studied,and the appropriate concentration was selected for compounding with MXene.During the exploration of PAN/MXene composite fiber,the effects of different MXene content on the microstructure,electrical conductivity,mechanical and electrochemical properties of the composite fiber were investigated,which provided basic data for further exploration of fiber electrodes with superior comprehensive electrochemical properties.The results show that PAN spinning solution can be prepared into several meters of continuous fibers by wet spinning,and then it can be pre-oxidized and carbonized into high-strength conductive PAN carbon fibers.The introduction of different contents of MXene can alleviate the skin-core phenomenon in the fiber solidification process to a certain extent,and form more folds on the fiber surface,which is beneficial to the infiltration and diffusion of electrolyte.When the content of MXene is 25 wt%,the comprehensive performance of the fiber electrode is the best.The strength,conductivity and specific capacitance can reach 13.24 MPa,696.37 S/m and 112.13 F/g,and the capacitance retention rate can reach 95.83% after1000 GCD cycles.In order to further balance the mechanical and electrical properties of fiber electrode,the performance of fiber electrode can be optimized by reasonable structural design.Firstly,the influence of pore structure on the performance of PAN electrode was explored,and the pore-forming agent PMMA was selected.The influence of PMMA ratio on fiber strength and electrochemical performance in PAN/PMMA blended spinning system was systematically investigated.Secondly,PAN/PMMA and PAN/MXene were used as core or shell spinning solutions for coaxial wet spinning,and the effects of different sheath-core material configurations on the mechanical,electrical and electrochemical properties of coaxial fibers were discussed.The results show that when the mass ratio of PAN:PMMA is 9:1,the porous PAN carbon fiber presents the best comprehensive performance.A variety of coaxial fibers were successfully prepared by coaxial wet spinning process,among which PAN/MXene@PAN/PMMA coaxial fibers showed the best comprehensive properties,reaching the balance between mechanical properties and electrochemical properties.The tensile strength,electrical conductivity and specific capacitance reached 14.4 MPa,322.7 S/m and 113.18 F/g,respectively.On the basis of the first two chapters,PM25 and PAN/MXene@PAN/PMMA coaxial fibers with good comprehensive properties were selected as electrode materials to assemble symmetrical supercapacitors and their electrochemical properties were tested.In order to further improve the energy density of supercapacitor,an asymmetric supercapacitor was designed.PM25 fiber was selected as the matrix,and its surface was grafted with polyaniline.The effects of growth time and aniline concentration on the comprehensive properties of the modified fiber were investigated.Finally,the modified fiber and PAN/MXene@PAN/PMMA coaxial fiber were assembled into an asymmetric supercapacitor,and its electrochemical performance was tested.The results show that when the reaction time is 80 minutes and the aniline concentration is 100 m M,continuous and uniform polyaniline can be formed on the fiber surface,and the specific capacitance of the modified fiber electrode can reach 225.1 F/g at 0.25 A/g current density.Symmetrical supercapacitors composed of different fibers show good electrochemical performance.The specific capacitance and cycle stability of PM25,coaxial fiber and modified supercapacitor are 14.4 F/g and 80%,12 F/g and 82.8%,25.13F/g and 77.2% respectively.The specific capacitance and cycle stability of the asymmetric supercapacitor assembled by modified fiber and coaxial fiber are 22.5 F/g and 75.5%respectively.At last,when PM25,coaxial fiber,PP80 fiber and asymmetric supercapacitor are applied to different working voltage windows,they can reach 1.4 V,1.4V,0.9 V and 1.7 V respectively,and their energy densities can reach 3.13 Wh/kg,3.35 Wh/kg,2.97 Wh/kg and4.36 Wh/kg respectively.To sum up,the fiber electrode prepared in this study has good mechanical and electrochemical properties,long cycle life and good application prospects. |
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