DEVELOPMENT AND FABRICATION OF A 1.5 F - 5 V SOLID ELECTROLYTE SUPERCAPACITOR

This paper deals with the fabrication of a prototype of supercapacitor based on activated carbon and solid polymer electrolyte. The supercapacitor named ITAECAP-1 has been entirely developed at CNR-ITAE of Messina, is formed by five stacked cells and has capacitance 1.5F and working voltage 5V. The prototype has been realized using Nafion polymer (Du Pont) both as electrolyte membrane separating the electrodes and as binder/electrolyte in the electrodes. All the electrodes of prototype have the same carbon and Nafion loading. The electrode has been prepared by a casting procedure that consists in spreading with a film applicator the ink, obtained by mixing activated carbon, Nafion ionomer electrolyte, graphite fibers and solvents, on a glass plate. After the evaporation of the solvents, the formed film (electrode) is thermally treated and purified in sulfuric acid solution. Then several rinsing with hot distilled water are made before the electrode is assembled with the electrolyte membrane by a hot pressing procedure. The activated carbon material has been furnished by Norit Italia S.p.A. (Ravenna, Italy) and has surface area 1500 m2/g. Graphite fibers are cut from a carbon fabric (Avcarb 1071) furnished by Ballard Material Products (MA, USA). The introduction of the graphite fibers in the final electrode allows to obtain a more robust and conductive layer. Nafion ionomer, introduced in the electrode, has both the functions of binding agent of carbon particles and fibers, and of proton conductor. The latter function is very important for the performance of the final capacitor because the presence of electrolyte inside the layer greatly extends the active interface between the ionic and electronic components of the electrodes. Nafion 115 membrane, with 1100 equivalent weight and thickness 150 micron, has been used as ionic conductive material between the electrodes. The five single cells stacked in the supercapacitor were separated by four bipolar plates of carbon fiber paper (AvCarb P50T by Ballard Material Products). Two end monopolar plates of carbon fiber paper made the contact between the external cells and the metallic external plates. The latter consists of titanium foil of thickness 250 micron fixed on more robust aluminum plate (thickness 2 mm). The aluminum plate was used to keep the titanium plate flat in the prototype.