Organic redox flow batteries (RFB) are possible alternatives to aqueous redox flow systems for large scale energy storage. The advantages of organic based RFB’s over aqueous systems are increased solubility of redox couple and a larger voltage operating window. A sodium based system is of interest due to sodium’s low cost and natural abundance. One major obstacle for organic RFB’s is the lack of available membranes that can withstand the harsh conditions of the system. A membrane for RFB needs to possess sufficient mechanical strength, high conductivity, ion selectivity and excellent chemical resistance. In this project, mechanically robust, chemically resistant, crosslinked membranes have been fabricated via thermal curing or UV curing. In one system, crosslinked poly(ethylene oxide)-based membranes containing 10 wt% to 40 wt% sodium triflate have been characterized as dry and plasticized samples. Membranes are free standing, flexible and robust with and without plasticizer. Specific ionic conductivity is governed by the polymer’s segmental dynamics and coordination of the anion and cation. Specific ionic conductivity for dry membranes ranges from 1.5 x 10-8 S/cm to 3.0 x 10 -6 S/cm at 20°C. Infrared and Ramen spectroscopy indicates formation of ion-aggregates and ion pairs when the sodium triflate concentration exceeds 24 wt%, elucidating the trend of the ionic conductivity. Glass transition temperature (Tg) increases from -40 °C to -6 °C as sodium triflate content increases from 10 wt% to 40 wt%, while Tg of plasticized membranes were almost constant around -55 °C. Furthermore, our efforts on the synthesis and characterization of sodium sulfonate functionalized crosslinked membranes will also be discussed.
Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.