Preparation and Characterization of Electric Double-Layer Capacitors Having a 3D Stainless-Steel Fiber Sheet as the Current Collector.

Abstract

One strategy to improve the performance of electric double-layer capacitors (EDLCs) is changing the current collector material. In this study, a three-dimensional porous current collector comprising stainless-steel fibers is fabricated using a relatively simple method. Capacitor properties of the EDLC using this unique current collector are characterized by cyclic voltammetry and charge–discharge tests. The voltammograms of the EDLC develop a more butterfly shape and an increased specific capacity at higher electrolyte concentrations. It shows reversible charge–discharge potential profiles, little capacity degradation (∼98% of the initial capacity at 1000th cycle), and a good rate performance at higher electrolyte concentrations (90% capacity retention for 2.5 times increase in discharge current). Its capacitance values (95–99 F g–1) are roughly twice the specific capacitance of an EDLC using the flat stainless-steel plate current collector (51 F g–1) without any performance degradation even at a higher loading of electrode active materials. Based on the AC impedance analysis, these good properties are attributed to the reduction in several resistances compared to the case of a flat stainless-steel plate: (i) the contact resistance between the electrode active material and the current collector, (ii) the resistance of the electrolyte in the finely branched space formed by the fibers and the active material, and (iii) the resistance in the diffusion layer. Increasing the electrolyte concentration further reduces the latter two resistances and the bulk electrolyte resistance, resulting in higher performance of the EDLC using the stainless-steel fiber sheet current collector.