Preparation And Performance Of Carbon Nanotube Composite Flexible Electrode And Its Super-capacitor Application

Carbon materials such as activated carbon,carbon nanotubes and graphene have emerged as research hotspot in energy storage area on account of their superior electrical conductivity,colossal specific surface area and chemical stability.Among these carbon materials,carbon nanotubes(CNTs),served as one-dimensional materials,have a diversity of macroscopic assemblies.They can be divided into three kinds according to the dimensionality of the assemblies.First are one-dimensional fibers and ribbons.Second are two-dimensional carbon cloth,carbon paper made by wet process and carbon nanotube films collected through floating chemical vapor deposition.The last are wet synthesized carbon gel,socks and foams prepared by floating chemical vapor deposition and vertical aligned carbon nanotube arrays growth on silicon substrate.At present,an important develop direction in energy storage area is to exploit soft,even elastic energy storage devices.Here,flexible substrate and structure design of the electrode are where the shoe pinches.Besides,many efforts have been made around how to improve the specific energy density and power density of the devices.For this purpose,this dissertation has compared the mainstream aqueous dispersants and optimized the dispersing process to prepare a stable dispersed single-walled carbon nanotube aqueous dispersions.Then,using the as prepared carbon nanotube dispersions to prepare flexible composite carbon nanotube papers,that comprised of large-diameter carbon nanotubes and single-walled carbon nanotubes.Next,polyaniline has been deposited on these composite papers and cloth as active materials to fabricate symmetric capacitor.Afterwards,the electrochemical charging and discharging mechanism of the polyaniline symmetric capacitor was studied based on the carbon nanotube/polyaniline composite papers and cloth.Last,a new system of the asymmetric capacitor structure has been designed in order to further expand the working potential window of the capacitor and improve the energy density of the device.The main research content and innovation of this dissertation are stating as follows:Using commercial single-walled carbon nanotubes as raw materials and matching with different dispersants quantitatively analyzed the dispersion effect of different dispersants according to the hanging level and the residual quality of the supernatant after ultrasonic dispersion and high-speed centrifugation.Thereinto,Sodium dodecylbenzene sulfonate(SDBS)has the best comprehensive performance.Therefore,a dispersed and stable aqueous single-walled carbon nanotube dispersion has been prepared with SDBS as dispersant.Using highly dispersed and stable single-walled carbon nanotubes dispersions and large diameter carbon nanotube dispersions as raw materials,composite carbon nanotube paper with excellent flexibility have been prepared using vacuum filtration method.Because of its synergistic multilevel structure,it shows excellent properties that common commercial carbon nanotube paper and pure single-walled carbon nanotube paper do not possess,such as:1,excellent tensile strength(27 MPa)and flexibility;2,the specific capacitance is as high as 159 F g~-11 because of the utilization of single-walled carbon nanotubes is greatly increased.After furthering electrodeposition of polyaniline on the surface of the composite carbon nanotube paper,the specific capacitance of the composite membrane is even bigger than the pure single-walled carbon nanotube film and saves the cost due to the use of expensive single-walled carbon nanotubes has been reduced.The carbon nanotube/polyaniline composite films are used as the electrode material to form a symmetric capacitor.A standard electrode is chosen as reference and voltage change of the symmetrical capacitor is recorded by voltmeter to explore the charging and discharging mechanism of the polyaniline symmetrical capacitor.It is find that the working voltage range of the two poles is narrow and the active material is not fully charged and discharged at the two poles,which leads to the low energy density of the devices.In order to obtain capacitors with high energy density,we turn our eyes to asymmetrical supercapacitors,which can broaden the working potential window and thus increasing the energy density.The charging and discharging mechanism of the asymmetric capacitor system is also explored.