Electrospun Carbon Fibers Replace Metals as a Current Collector in Supercapacitors

The final step toward a completely metal-free electrochemical energy device requires the replacement of the metal current collector with conductive carbon. This article describes the use of carbon fibers derived from electrospun poly(ionic liquid) as the current collector. Fibers were stabilized by ionic cross-linking with a small organic acid, followed by heating to 950 degrees C under N-2 to create a conductive and free-standing carbon fleece. The resultant carbon fibers were utilized as current collectors in EDLCs in both aqueous (1 M Na2SO4 in water) and organic (1 M tetraethylammonium tetrafluoroborate in acetonitrile) electrolytes. In both cases, carbon fibers outperformed the established carbon-coated aluminum foil and showed performances comparable to platinum. They operated at current densities of up to 40 A g(-1) without significant signs of resistivity. We found that both the nanostructure resulting from spinning and the use of PIL as a carbon precursor are crucial in obtaining this performance. These carbon fibers are only 2-10% the weight of the aluminum current collector and thus increase the gravimetric energy density of the whole cell. PIL-derived carbon fibers could be a promising inexpensive and metal-free alternative for future electric double-layer capacitor applications.