Low Cost and Highly Selective Composite Membrane for Redox Flow Batteries

Redox flow batteries (RFB) hold great promise for large scale electrochemical energy storage that will be required for intermittent renewable energy sources like solar or wind. A critical component of the RFB is the membrane which separates anode and cathode compartments. Currently, this is primarily Nafion, but Nafion is not only too expensive, but also lacks in selectivity, permitting leakage between anode and cathode electrolyte compartments. EIC Laboratories proposes the development of a new composite membrane for RFB applications. The membranes will be based on inexpensive feedstocks providing an economical alternative to Nafion and other perfluorinated copolymers, with additional improved selectivity properties. Furthermore, the membrane is to be solvent castable, providing an economical pathway for large scale production. The Phase I results successfully met the stated goals of the Phase I proposal, which were to develop and synthesize a composite membrane using a novel amphiphilic block copolymer, demonstrate a membrane casting technology, and demonstrate the advantages of the new membrane system in a laboratory scale vanadium redox battery (VRB). The new separator is shown to be stronger than Nafion with similar conductivity and stability, yet with much reduced self-discharge and meeting the proposed cost objectives for large scale manufacture. The Phase II program will assess the tradeoff and optimization of membrane properties, including selectivity and conductivity as a function of polymer structure variation, mechanical strength, and long term chemical stability in the VRB cell environment. The cost of materials and processing will be further optimized to bring the total membrane cost to & lt;$50 per square meter. The new membranes will be further characterized and optimized for their performance in experimental VRB cells of increasing scale in order to provide a transition to Phase III. Membrane samples totaling 1 m2 will be delivered to DOE for evaluation, including 100 cm2 by the end of year 1. Commercial Application and Other Benefits: The energy storage applications of RFBs may offer the benefits of improving transmission grid reliability and increase effective transmission capacity. They also provide great benefits for load leveling from variable renewable sources such as wind and solar power.