The Application Of Electrospun Micro-nanofiber Yarns In Supercapacitor

At present,with the increasing popularization of wearable and portable electronic devices such as Apple mobile phones and Google glasses,flexible wearable devices(such as smart clothes)have become the focus of researchers.Energy storage devices(supercapacitors,lithium batteries,etc.)are the integral part of smart apparel.Among them,flexible one-dimensional structure supercapacitors have been extensively studied due to their high power density,long cycle life and integration with smart clothes.Electrospun nanomaterials are used in supercapacitor electrode materials due to their large specific surface area,small size and light weight.However,there is less research on one-dimensional electrospun nanofiber yarns in supercapacitors.Therefore,in this paper,we will use the electrospun micro-nanofiber yarns as the carrier,a series of one-dimensional supercapacitor electrode materials with different structures are designed and the properties of the electrode materials will also be investigated.Firstly,small amount of PANI was coated on the surface of non-conductive PAN nanofibers to explore PANI layer morphology of the conductive properties by using vapor-phase polymerization method.PAN micro-nanofiber yarns were prepared by using the yarn spinning machine developed by our research group as the core material.Then the vapor-phase polymerization method was used to coat PANI on the surface of PAN micro-nanofiber yarns to form the PAN/PANI composites nanofiber yarns.The influence of various parameters on the morphology and electrical properties of PANI on the surface of composite yarn was investigated by single factor experiment.The experimental results showed that when the concentration of oxidant was 0.375mol/L,the polymerization time was 5h,the concentration of hydrochloric acid was 1mol/L,the polymerization temperature was 20 ?,the morphology of the PANI coated was the most uniform and continuous.The conductivity of the composite yarns reached to(3.15±0.19)S/m;The supercapacitor properties of the PAN/PANI yarns were tested under the conditions of a current density of 0.1 m A/cm2,the areal specific capacitance of the PAN/PANI yarn was 39.2 m F/cm2.Secondly,since PAN is a non-conductive polymer,its own resistance is very large and it is not suitable for the preparation of electrode materials,conductive carbon nanofiber yarn(CNY)is selected as the core material.Due to the high carbon content of PAN,PAN micro-nanofiber yarns are carbonized to obtain carbon nanofiber yarns.Scanning electron microscopy(SEM),infrared spectroscopy(FTIR),thermogravimetry(TG)and Raman spectroscopy(Raman)and electrochemical workstation were used to characterize the structure and performance of CNY.The experimental results show that the nanofibers still have high orientation in CNY,the stratified graphite structure still exists in CNY.The conductivity of the CNY is about one order of magnitude higher than PAN/PANI so the conductivity is improved;The areal specific capacitance of the carbon nanofibers was 4.22 m F/cm2 and 4.96 m F/cm2,respectively,at a scanning speed of 5 m V/s and a current density of 0.1 m A /cm2.Due to the limitation of energy storage in the electric double layer capacitor of the carbon-based material and the further improvement of the areal specific capacitance of the electrode material,conductive polymer polyaniline was introduced into the surface of the core carbon nanofiber yarns,PANI was successfully coated on the surface of CNY by the means of aniline dilute solution in-situ polymerization to obtain CNY/PANI composite yarn electrodes.The supercapacitor performance of the CNY/PANI composite yarn electrode materials prepared at different concentrations of ANI.The experimental results showed that the other conditions remain unchanged,when the aniline concentration is 0.02 M,CNY/PANI composite yarn has the highest areal specific capacitance,The areal specific capacitance is 99.8m F/cm2 at the scanning rate of 5m V/s and the specific capacitance is 116 m F/cm2 at the current density of 0.1m A/cm2,compared with pure CNY yarn,the supercapacitor performance has been obviously increased.Combined with the FESEM image,the growing processing of PANI with different morphologies on the CNY and the reasons for the formation of the morphological features were also preliminarily discussed.Finally,in order to further enhance the mechanical strength and electrochemical performance of the yarn electrode and make it more widely used in the processing and weaving of smart textiles,in this paper,a new kind of core-spun yarn was designed.Carbon fiber with high conductivity and mechanical strength as the core layer and micro-nanofiber yarns as the shell layer were carbonized and polyaniline treated to produce carbon fiber/carbon nanofiber yarn/polyaniline(CFs/CNYs/PANI)composite yarn electrode material.The structural performance of CFs/CNYs /PANI was tested by FESEM,TG,Land battery test system and other testing instruments.The results showed that when the other conditions were not changed,the specific capacitance of the CFs/CNYs/PANI composite yarn electrode was the highest when the concentration of aniline was 0.02 M,at the current density of 0.1m A/cm2,the maximum areal specific capacitance was 234 m F/cm2 and the energy density can reach 5.2?Wh/cm2 at a power density of 0.2W/m2.After 8000 cycles,The areal specific capacitance of CFs/CNYs/PANI composite electrode materials remained about 89% of the original,showing the excellent cycling stability.