Preparation And Electrochemical Properties Of Flexible Supercapacitors Based On Carbon Nanotube Fibers

As a new type of electrochemical energy storage device,supercapacitors have attracted much attention due to their high-power density,long cycle life and environmental friendliness.Carbon nanotubes（CNT）fibers not only have the unique properties of CNTs but also possess the excellent flexibility and portability of fibers,which makes them very suitable as electrode materials for flexible supercapacitors.However,the low specific capacitance and energy density of pure CNT fiber supercapacitors limits their practical application as electrochemical energy storage devices for flexible wearable electronic devices.In order to improve the electrochemical performances of CNT-based supercapacitors,the composite fiber electrode was prepared by loading other active materials on the surface of CNT fiber by different methods,and then was assembled into high-performance flexible solid supercapacitors.The main results of this paper are as follows:（1）The CNT/GO composite fibers were obtained by loading GO on the surface of CNT fibers using electrophoresis deposition method,and then the CNT/GO composite fibers were reduced by hydroiodic acid to obtain CNT/r GO composite fibers.After that,these composite fibers were assembled into symmetric supercapacitors,respectively.The loading of GO with higher specific surface area provides more active sites for charge at the interface between the electrodes and the electrolyte.The results of electrochemical performance analysis shows that specific capacitance of CNT/GO fiber supercapacitor（43.14 F/cm³）and energy density（0.54m Wh/cm³）is significantly higher than the pure CNT fiber supercapacitor（10.69 F/cm³ and0.238 m Wh/cm³）.In addition,more surface defects will be formed after the chemical reduction of GO,which can improve the specific capacitance and rate capability of CNT/r GO fiber supercapacitor.（2）The CNT/GO-MnO₂composite fibers were prepared by loading MnO₂ on the surface of CNT/GO composite fibers using electrochemical deposition method,with the CNT/Mn O₂composite fibers as control samples that were prepared by electrochemical deposition method on the surface of pure CNT fibers.The CNT/GO-Mn O₂ and CNT/Mn O₂ composite fibers were assembled into symmetric supercapacitors,respectively.CNT fiber as the substrate of Mn O₂has high electrical conductivity,which is conducive to charge transfer.And Mn O₂ has excellent pseudocapacity performance.Finally,the introduction of GO is beneficial to the nucleation of Mn O₂ and makes up for the shortcomings of poor electrical conductivity of Mn O₂.The results of electrochemical performance analysis shows that the specific capacity（244.53 F/cm³）and energy density（5.43 m Wh/cm³）of CNT/GO-Mn O₂ fiber supercapacitor is about 2.4 times higher than those of CNT/MnO₂ fiber supercapacitor and about 22.8 times higher than those of pure CNT fiber supercapacitor.（3）Black phosphorus（BP）is a new two-dimensional energy storage material with good conductivity and high specific surface area.The CNT/Mn O₂-BP composite fibers were obtained using liquid phase method of in-situ reducing of KMn O₄ into Mn O₂ on the pure CNT fibers surface by BP.For comparison,CNT/Mn O₂ composite fibers were prepared by liquid phase method in the absence of BP.After that,the CNT/Mn O₂-BP and CNT/Mn O₂ composite fibers were assembled into symmetric supercapacitors respectively.The results of electrochemical performance analysis shows that the specific capacity（441.79 F/cm³）and energy density（9.82m Wh/cm³）of CNT/Mn O₂-BP fiber supercapacitor are about 2.4 times higher than those of CNT/Mn O₂ fiber supercapacitor,and about 37.9 times higher than those of pure CNT fiber supercapacitor.This is mainly attributed to the excellent pseudocapacitance of Mn O₂ and the colloid stabilized mechanism of H_xPO_y between MnO₂ layers can promote faster ion transport.