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Carbon nanotube and polypyrrole supercapacitors Izadi-Najafabadi, Ali

Abstract

Supercapacitors are electrochemical devices intended to combine the high power density of conventional capacitors with the high energy density of batteries. They can store energy electrostatically at the interface between a metal electrode and an electrolyte (double layer capacitance) and/or Faradaic energy storage through reversible successive redox processes (pseudocapacitance). The amount of accessible surface area of the electrode to the electrolyte and the amount of time required for electronic charges and ionic charges to reach the electrode/electrolyte interface are the performance determining factors. 15 electrolytes are evaluated for their ionic conductivity and potential operating range. Among organic electrolytes NaPF6 dissolved in acetonitrile is determined to have the highest conductivity at 4.65 S/m. The operating voltage range of all electrolytes are limited due to impurities. Different types of polypyrrole, a conducting polymer, exhibiting double layer capacitance and pseudocapacitance are examined under different operating conditions. Among the ten different types of polypyrrole films evaluated, the best film achieves a maximum discharge energy density of 16.6 (J/g) and a maximum discharge power density of 1.15(W/g) according to single electrode measurements. To improve the performance of the polypyrrole films, composite electrodes based on electrodepositing polypyrrole on carbon fiber paper are produced. A cell based on these electrodes achieves a maximum discharge energy density of 12.5 (J/g) and a maximum discharge power density of 0.0134 (W/g) based on the mass of both electrodes. A novel carbon nanotube film fabrication method is employed to assemble supercapacitor cells with carbon nanotube electrodes. The best performing cell achieves a maximum discharge energy density of 4.79 (J/g) and a maximum discharge power density of 1.6 (W/g).

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