Preparation And Properties Of Flexible Solid-state Supercapacitors Base On Carbon Nanotube Yarns

In a variety of energy storage devices,the supercapacitor is one of the most widely used new electrochemical energy storage devices.Carbon nanotube(CNT)yarns are ideal electrode materials for linear flexible solid-state supercapacitors.But their poor capacitance and energy density limit their use as energy storage device of wearable smart textiles.In this paper,carbon nanotube yarns serve as the substrate.The performances of yarn supercapacitors are improved by changing the compositions and structure of the electrode materials as well as the electrolyte,resulting in flexible solid-state supercapacitors with high capacitance and high energy.The main points of this thesis are as follows:(1)The nanoparticles Co3O4 and NiO are deposited on the surface of two carbon nanotube yarns by electrodeposition to prepare carbon nanotubes/nanoparticles composite yarn electrodes,and then they are assembled into two kinds of supercapacitors(CNT/Co3O4 and CNT/NiO).The CNT yarn with larger surface area and porous structure provides a depositional space for the nanoparticles,and the transition metal oxides provide high pseudocapacitance,so that the resulting supercapacitors have higher specific capacitance,energy density and good mechanical properties.The CNT/Co3O4 yarn supercapacitor has the highest specific capacitance(42.47 F/cm3)and the energy density(0.94 mWh/cm3)among all samples,which are 2.82 times and 2.84 times as high as that of pure CNT yarn supercapacitor respectively.(2)The transition metal oxide particles Co3O4 and NiO are simultaneously deposited on a carbon nanotube yarn by electrodeposition.Then the obtained yarn is immersed in the graphene ink to obtain a three-layer composite yarn(carbon nanotube yarn/ nanoparticles/ graphene),which is assembled into a symmetrical supercapacitor(CNT/Co3O4@NiO/GN)with good mechanical properties.Its specific capacitance(263.34 F/cm3)and energy density(5.86 mWh/cm3)are about 23 times that of pure CNT yarn supercapacitor respectively,and about 6 times that of above-mentioned CNT/Co3O4 yarn supercapacitor.It can be attributed to the large surface area and high conductivity of the graphene.(3)A carbon nanotube/stainless steel monofilament(CNT/SS)core-spun yarn is obtained by introducing a stainless steel monofilament into the CNT yarn as the current collector.Supercapacitor based on CNT/SS core-spun yarn and CNT yarn electrodes are prepared by using ionic liquids gel electrolyte(CNT@IL and CNT/SS@IL),respectively.Compared with the supercapacitors based on PVA-KOH electrolyte,the CNT/SS@IL is a solid-state supercapacitor with higher electrochemical performances and good mechanical properties.Its specific capacitance(263.31 F/cm3)and energy density(66.65 mWh/cm3)are about 17 times and 200 times that of CNT/SS@PVA-KOH yarn supercapacitor,respectively.The CNT/SS@IL supercapacitor shows higher electrochemical performances on account of the high conductivity of stainless steel wire and the wider voltage window caused by ionic liquid electrolyte.In addition,the addition of stainless steel wire also facilitates the expansion of the length of the supercapacitor so that it is suitable for power sources of larger wearabale electronic devices.(4)Supercapacitors(Co3O4 /CNT/SS and MnOx/CNT/SS)are based on composite yarn eletrodes,which are prepared by electrodeposition of the nanoparticles Co3O4 and MnOx on two different CNT/SS core-spun yarns.The MnOx/CNT/SS yarn supercapacitor is flexbile and robuts enough and exhibits the best electrochemical performance and mechanical properties.Its specific capacitance(217.61 F/cm3)and the energy density(4.84 mWh/cm3),are all about 7.5 times as high as that of CNT/SS yarn supercapacitor.Because of these,the MnOx/CNT/SS yarn supercapacitor can be used as textile electronic devices.