Development of Supercapacitor Slurry Cathode in Aqueous Sodium-Air Batteries using Mussel-Inspired Binder

Abstract

Seawater batteries (SWBs) which are considered as a promising energy storage system because of its cost-effective and eco-friendly characteristics. As a source for sodium ion, SWBs use naturally abundant seawater, which can dramatically reduce the cost of cathode. However, improvement of the SWBs performance is still a challenge due to the extremely slow kinetics of the cathode reaction (i.e. oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)). Even though it is known that the supercapacitor slurry cathode using activated carbon powder (ACP) with large surface area can noticeably improve the OER/ORR kinetics, the commercial binders (e.g. Polyvinylidene fluoride (PvdF)) cannot be used due to the poor water wettability. Herein, we synthesized a novel catechol-based random copolymer (DPA642) through thermal copolymerization using two monomers: i) dopamine methacrylate (DMA), which exhibits antioxidative and underwater adhesive properties, and ii) poly(ethylene glycol) (PEG), which is hydrophilic in nature. Using the synthesized polymer binder, we fabricated a slurry cathode which is made from hydrophilic activated carbon powder (ACP). The SWBs with ACP-DPA642 composite cathode showed reduced voltage gap (0.62 V) and higher energy efficiency (94.5%) compared to activated carbon cloth (ACC) (1.74 V, 64.8%) and ACP-PvdF cathode (1.48 V, 84.5 %) after 100 cycles in a charge-discharge cycle test carried out at a current density of 0.13 mA cm-2 for 5 h.