Sintered Electrospun Fibrous Electrodes via Compression and Laser Perforation for Redox Flow Battery

Abstract

The principal sources of new renewable energy, such as solar and wind power, depend strongly on the weather conditions, leading to the unstable electric power supply. Energy storage systems (ESS) has been developed to address this problem. One of the most promising technologies for energy storage device is redox flow batteries due to its high capacity and design flexibility. In particular, the vanadium redox flow battery is considered as a next-generation battery because of its safety and high efficiency, but not yet widely deployed owing to its low power density. The carbonized electrospun fibrous materials have been utilized as electrodes to overcome the flaw, because of their high specific surface area for reaction, high porosity to support flow and diffusion, and good electrical conductivity through the interconnected fibers. Typically, smaller fiber is preferential due to the exponential increase of surface area, but the small pores among the fibers reduce the permeability, limiting the electrolyte transportation or increasing parasitic pumping costs. In this study, flow battery electrodes made of electrospun carbon fibers were synthesized by applying compression during the stabilization stage. The objective was to create flow battery electrodes with higher volumetric surface area to support the electrochemical reaction while retaining the permeability. A porosity reduction of 12% was attained by this method, yielding a 50% increase of volumetric surface area, while the in-plane permeability and tortuosity were found to remain consistent. In addition, the holes perforated by a carbon dioxide laser addressed the issue of low through-plane permeability caused by the compacted fibers. All electrospun samples outperformed commercial carbon mats in flow cell tests. The compressed samples showed markedly better performance in the activation region but showed serious mass transport polarization at higher current density. The laser perforations significantly eliminated this flaw, yielding the best performance over the entire range of current density. Figure 1