Preparation And Properties Of Flexible Supercapacitors Based On Carbon Nanotube Fiber

With the continuous development of science and technology,portable wearable electronic products such as smart clothing,smart watches and activity trackers have been widely used,which has dramatically changed the human lifestyle.However,these smart electronic products require more suitable storage devices to match.Nowadays,electrochemical energy storage devices are playing an increasingly significant role since the oil crisis and environmental problems become more serious.The supercapacitor developed in the 20th century is a kind of effective electrochemical energy storage product.Due to fast charge/discharge rate,long cycle life,wide temperature range and non-pollution,supercapacitors have achieved extensive attention of the researchers at home and abroad.In particular,fiber-based supercapacitors can be implanted into wearable electronic devices thanks to their light weight,small size,high flexibility and stitchability,which has great commercial application prospects.However,the current researches on fiber supercapacitors have the following problems:（1）low energy density limits its practical application,（2）with poor mechanical stability,supercapacitors cannot maintain high electrochemical performance under mechanical deformation,and（3）complex preparation strategies or long cycle are not conducive to industrial production.In consideration of the above problems,the carbon nanotube fiber,possessing excellent conductivity and high flexibility,was used as a substrate,with a simple and efficient method to modify the fiber electrode in order to prepare fiber supercapacitors with high performance and excellent mechanical stability in our work.The strategies demonstrated in this paper are low-cost,highly efficient and easily operated,which enable it to be promising as reference for preparing high-performance fiber supercapacitors to meet the requirements for portable energy storage devices and wearable electronics.The specific research content of this paper is as follows:（1）Three-dimensional porous carbon nanotubes（CNTs）network structure was prepared on the surface of carbon nanotube fibers（CNF）by low-potential electrophoretic deposition method and further electrochemically depositing polyaniline（PANI）to obtain CNF/CNTs/PANI double core-sheathed structure.The fiber electrodes were attached to the surface of the flexible polydimethylsiloxane film in parallel,and the flexible supercapacitor was acquired by covering with PVA-H₃PO₄ gel electrolyte.The electrochemical performance and mechanical stability of the as-prepared supercapacitor were studied.The experimental results show that the all-solid-state supercapacitor with a double core-sheath structure has a high specific capacitance of 67.31 mF cm^-2 at a current density of 0.5 mA cm^-2.After 5000charge/discharge cycles,the specific capacitance loss is less than 10%.In addition,the supercapacitor also has high mechanical stability and the capacitance hardly changes under different deformations.In addition,the capacitance of 99.8%can still be maintained after 500cycles repeated bending from 0°to 180°.（2）Three-dimensional porous carbon nanotubes/polypyrrole（CNTs/PPy）and reduced graphene oxide（rGO）were respectively deposited on the surface of carbon nanotube fibers by electrochemical deposition to form a core-sheathed structure.An all-solid-state asymmetric fiber-shaped supercapacitor was assembled by wrapping the PVA-H₃PO₄ gel electrolyte coated negative CNF/rGO electrode along the positive CNF/CNTs/PPy electrode.The effects of deposition time（50s,100s,200s,300s）on the performance of the CNF/CNTs/PPy electrodes and the electrochemical performance,cycle stability and mechanical stability of asymmetric supercapacitors were investigated.The experimental results show that the CNF/CNTs/PPy electrode has the highest areal specific capacitance with the deposition time of 200 s,reaching to 184.5 mF cm^-2.The potential window of the asymmetric supercapacitor is widened to 1.6 V,the areal specific capacitance is 58.82 mF cm^-2,with the power density of 6.4 mW cm^-2 and the areal energy density of 20.91μWh cm^-2 at the current density of 0.5 mA cm^-2.Moreover,the capacitance of the supercapacitor remains substantially unchanged under any bending states.After undergoing 200 reciprocating bending cycles,an initial capacitance of 98.6%can still be maintained,exhibiting excellent mechanical stability.In addition,the supercapacitor was testified by 90%capacity retention after 10000 times of galvanostatic charge-discharge process.