| Supercapacitor is a new energy storage device, which has many advantages such as safety and no pollution, large capacity, ultrahigh power density, exceptional cycle life, a wide range of operating temperatures, etc. The properties of supercapacitor mainly depend on the performances of the electrode materials. Now main electrode materials are carbon materials(carbon nanotubes, graphene, carbon aerogel, etc.), metal oxide(manganese dioxide, titanium dioxide, vanadium pentoxide, etc.) and conductive polymers(polyaniline, polypyrrole, polythiophene, etc.). This paper used biomass cellulose as raw material and got cellulose nanofibers through chemical purification and mechanical grinding. Then, we used carbon nanotubes, graphene and polyaniline as supercapacitor electrode substrate materials and prepared composite electrode materials via different compound processes and analyzed the surface morphology and the electrochemical properties of the composite electrode materials by some test technologies such as FE-SEM, FTIR, RAMAN, XRD and electrochemical workstation, etc. The concrete research content is as follows:1. Through chemical purification and mechanical grinding, biomass cellulose was made into cellulose nanofibers. After being ultrasonic treated, the grinding fluid was directly pumped into film using vacuum filtration method and tested it on the related performance. Research shows that: after ultrasonic treatment, the diameter distribution of the cellulose nanofibers was more uniform, mainly distributed in 10~30 nm. Cellulose nanofibers film light transmittance could reach 87.5%, and the tensile strength increased from 68.03MPa(the film made from grinding fluid) to 109 MPa.2. After being ultrasonic mixed, different mass ratio of carbon nanotubes and cellulose nanofibers mixed liquor was pumped into a composite film by vacuum suction filter. After dryed the composite film and tested its related performance. Research showed that: The two were cross-wound, which played a role in enhancing their dispersion performance. While the mass ratio was 1: 1, the combined performance of the two got the best. The electrochemical tests found that cellulose nanofibers/carbon nanotubes electrode had excellent capacitance characteristics and cycle stability, specific capacitance could be achieved 35.9F/g at 0.2A/g current density, and specific capacitance could retain 96.8% after 1000 times charge-discharge at the current density of 1A/g.3. Using hydrochloric acid as the doping acid, ammonium persulfate as initiator, we controled different reaction time to fabricate conductive polyaniline via in-situ polymerization method. Made polyaniline and cellulose nanofibers into cellulose nanofibers/polyaniline composite electrode by the layer-by-layer self-assembly method and tested cellulose nanofibers/polyaniline composite electrode on the related performance. Research showed that: polyaniline conductivity would be the best when the polymerization time was 6 hours. The electrochemical tests showed that the cellulose nanofibers/polyaniline electrode had high specific capacitance, could reach 254.7 F/g at the current density of 0.2A/g. The charge transfer resistance was big, and the specific capacitance merely kept 57.6% after 1000 times charge-discharge at the current density of 1 A/g.4. First, the cellulose nanofibers/carbon nanotubes composite film was immersed in an acid solution of aniline, and then dropped the acid solution of ammonium sulfate to initiate polymerization, for polymerizng polyaniline onto the surface even inside of the cellulose nanofibers/carbon nanotubes composite film. After dried the ternary composite film, we got the flexible and foldable cellulose nanofibers/carbon nanotubes/polyaniline composite electrode and tested its related performance. Research showed that: the cellulose nanofibers/carbon nanotubes/polyaniline electrode had not only good cycle stability from carbon nanotubes but also excellent pseudocapacitance properties of polyaniline. Because of this, specific capacitance of the cellulose nanofibers/carbon nanotubes/polyaniline electrode can reach 216.0 F/g at the current density of 0.2A/g and specific capacitance retention rate was 81.7% after 1000 cycles at 1A/g, which suggested that it can be used as flexible and foldable supercapacitor electrode materials.5. Cellulose nanofibers and carbon nanotubes were ultrasonic mixed into mixture, then polyaniline was polymerized via in situ polymerization method in the solution. Polyaniline coated on the surface of the cellulose nanofibers and carbon nanotubes, then the mixture was freeze-dried for the cellulose nanofibers/carbon nanotubes/polyaniline aerogel, last the aerogel was cold-pressed to get the cellulose nanofibers/carbon nanotubes/polyaniline aerogel film electrode and tested its related performance. Research showed that: due to its inherent characteristics of qualitative light and porous, the cellulose nanofibers/carbon nanotubes/polyaniline aerogel film electrode greatly improved the electrolyte diffusion and absorption and the charge transfer resistance was very small. Besides, it had a high specific capacitance of 791F/g at 0.2A/g current density and the cycle stability is also very good, the initial capacity retention ratio was more than 82% though at a high current density of 4A/g discharging 3000 cycles.6. Composite film electrode was prepared using layer self-assembly process, graphene intercalated in the composite material and prepared the cellulose nanofibers/carbon nanotubes/ grapheme/polyaniline composite electrode and then tested its related performance. Research showed that: layer structure of the composite electrode material became looser because of intercalation of graphene, which reduced the internal resistance of the thin film electrode. Due to excellent stability of graphene, cycle stability of the composite electrode was greatly improved, cycled after 1000 times the specific capacity remained 94.3% or more than the initial capacity. And the specific capacitance can reach 623.1F/g at 0.2A/g current density. |
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