| Supercapacitors are new energy storage components between batteries and electrostatic capacitors, which have higher power density and longer cycle life than batteries, and can be charged within a short time. They can be used as driving system of electric vehicles with batteries.The specific capacity of the exiting supercapacitors is still low, and the cost is high. This limits its wide application. The key words are the choice and optimization of the electrode materials. Nowadays there are activated carbon, carbon jell, metal oxide, carbon nanotube, etc. as carbon materials of effective electrode. However due to the high resistance, complicated technology, low capacity, high cost and hard processing, it is impossible to achive the industrial production.Because the resistance of activated carbon fibre is low, and its processing is easy, also it is suitable for working under high power and it can work for a long time, ACF could overcome those shortcomings of electrode materials. However the problems of its low intensity and low electrode capacity prohibit the wide and multi-variety application of ACF. But the intensity of present ACF is low, which limits the application in supercapacitor and other fields where require properties of both adsorption and intensity. However the study on ACF which from the angles of improving its intensity and electrod capacity is very few now.The aim of the thesis is to improve intensity of activated carbon fiber in order to expand the application in the super electric capacity apparatus material. We have chosen different precursors of ACF: Polynosic-based fibre, graphite-based fibre and Viscose-based fibre cloth. High-strength activated carbon fiber was prepared by optimizing the processing technology. And the electric property of activated carbon fiber was studied in detail.The results of study indicated that Polynosic-based fiber could be utilized as raw material to prepare activated carbon fiber. With the increase of phosphate solution concentration, phosphate solution content of the Polynosic fiber increases. The yield of activated carbon fiber is proportional to the phosphate solution content at all level of preparation. When the phosphate solution content is increasing, the surface areas of activated carbon fiber raise gradually, hit a maximum and then reduce; the intensity and the phosphate solution content of activated carbon fiber has the same relationship. Finally, a proper processing condition was found: Polynosic fiber infused in 10% phosphate solution firstly is pre-oxidized when the temperature increases gradually to 250℃, carbonized on 850℃, activated on 900℃. The prepared activated carbon fiber has larger surface area and higher intensity. Under the same condition, different precursor fibers were used to prepare activated carbon fiber separately. The results indicated that: Polynosic-based activated carbon fiber has relatively higher intensity and yield; the activated carbon fiber based on industrial rayon fiber has larger surface area but lower yield and intensity; rayon-based activated carbon fiber with high intensity has general properties.To prepare activated carbon fiber using graphite fiber has a more complicated processing. The activated carbon fiber with more 1400m~2/g surface area was prepared under the following condition: higher activation temperature (900℃), longer activation time(120 minutes) and vapor actibation. With the increase of activation time, the carbon content of activated carbon fiber reduced, hydrogen and nitrogen content increased, which may result from the increase of the other content.The electrical testing showed that the super capacitor prepared from Polynosic-and graphite-based activated carbon fiber exhibit better reversible performance. A series of super capacitors were prepared from Polynosic-based activated carbon fiber with different surface area as electrode material. The specific capacity of those super capacitors is proportional to the surface area. When it hit the maximum, such relationship disappeared. The activated carbon fiber can be prepared from high intensity graphite-based carbon fiber. The surface area increases gradually with longer activation time. They can be used as electrode material of high power super capacitor which exhibit better electrical performance.All in all, graphite-based ACF has better intensity and lower specific capacity; Polynosi-based ACF has higher intensity than others and higher specific capacity. Viscose-based ACF cloth has better intensity and wide application in high power super capacity. |
