Structural effects of anion exchange composite membranes in non-aqueous redox flow batteries

In this study, two different structured poly(diallyldimethylammonium chloride) (PDDA)/urushi composite membranes on porous supports were prepared, and their effects on the efficiency of non-aqueous Fe-Ni redox flow batteries (RFBs) were investigated. Chemically/mechanically stable urushi, which was thermally polymerized from urushiol, was chosen as the matrix, and PDDA was used as the anion-exchange material. A thin-layered composite membrane was fabricated by coating a PDDA/urushiol solution on top of the porous support. Moreover, a charged-porous structure was prepared by the penetration of a DDA/urushiol solution into the pores of the porous support, followed by thermal polymerization. The composite membranes exhibited reduced permeabilities; however, their ion conductivities were of the same order as that of the commercial FAP450 membrane. The coulombic efficiency (CE) and energy efficiency (EE) of the RFBs with charged-porous composite membranes were 90.7% and 76.2%, respectively; the CE and EE values were 79.0% and 68.7% for the nonaqueous Fe-Ni RFBs with thin-layered composite membranes, at a current density of 0.5 mA cm(-2), which are higher than those obtained with a commercial FAP450 membrane. These results indicate that controlled porosity in an anion-exchange material on a chemically and dimensionally stable porous membrane contribute to the successful application of RFBs in energy storage systems.