Designing Ionic Polymer Membranes for Large-Scale Flow Battery Energy Storage

New polymer membranes are needed to advance energy storage and conversion technologies for distributed and grid-scale applications. We have designed, characterized, and demonstrated ion-conducting polymer membranes that have achieved excellent performance and long-lifetime stability in vanadium redox flow batteries, a leading candidate for integration with renewable power networks and grid-scale energy storage systems with sizes ranging from 10s to 100s of megawatts. By tuning the nanophase self-assembly of the ionic domains in the polymers, we are able to increase the cycle life of the device by impeding vanadium ion transport through the membrane while facilitating high conductivity in the electrolyte. The tradeoff between transport properties, such as permeability and conductivity can be quantified by a figure of merit to help select the most desirable candidate membrane chemistries. We have shown that decreasing the vanadium permeability of the membrane by a factor of two, doubles the cycle lifetime of the device, which provides significant life-cycle cost savings. We have also demonstrated membranes with nearly zero vanadium permeability that show 100 % coulombic efficiency in flow battery charge-discharge cycling tests. Currently, we are working on demonstrating these membranes over 100s of charge-discharge cycles. In this talk, transport of ions, water, and active redox species through ion-containing polymer membranes and the design principles for new membranes will be discussed.