Pore-Filling Anion Exchange Membranes for Non-Aqueous Redox Flow Batteries (RFBs)

Redox flow batteries (RFBs) utilizing the oxidation and reduction of two soluble electroactive species for charging and discharging are promising energy storage devices. Most flow batteries are based on aqueous electrochemistry and are limited to low-voltage, inefficient systems. The voltage limit for aqueous electrolytes is 1.23 V because the cell potential must lie within the potential range where the solvent and electrolyte components are electrochemically stable. To overcome this limitation, non-aqueous RFB systems have been investigated.  Non-aqueous electrolytes can offer the possibility of wider stable potential windows and higher energy and power densities compared to those of aqueous electrolytes. Ion exchange membranes (IEMs) are one of the most important components for RFBs. A conventional IEM for a redox flow battery is mainly used to selectively separate ions in an aqueous system, and accordingly, ion mobility characteristics and film properties are optimized for the use in aqueous solution.  However, the characterization of IEMs for a RFBs using non-aqueous electrolyte solution has not been sufficiently studied yet. We have developed pore-filling type polymer membranes for non-aqueous RFB applications. In this work, we have systematically investigated the ion mobility characteristics through the membranes and film properties in a non-aqueous system to optimize the membrane performances. In addition, the characteristics of novel non-aqueous RFB system employing dual complexes as redox couples and lab-made pore-filling anion-exchange membranes have been evaluated. We conducted flow battery test employing above-mentioned pore-filling type polymer membrane with non-aqueous electrolyte system. In order to increase performance we introduced new metal foam electrode with carbon coated on surface. Especially our non-aqueous electrolyte system showed above 80% energy efficiency.

This work was supported by the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Ministry of Knowledge Economy, Republic of Korea (No. 2011201010007A)