Highly Stable and Flexible Nanoporous Membranes for Non-aqueous Redox Flow Batteries

Non-aqueous redox flow batteries (RFBs) have a number of desirable properties and have the potential to achieve significantly higher energy densities than aqueous systems. However, currently the separators used in non-aqueous RFBs are mainly commercial membranes, which are originally designed for other applications. Therefore, many problems appeared when they are applied in non-aqueous RFBs directly. Development of highly ion-selective membranes that resist swelling and are mechanically robust in the non-aqueous electrolyte environment could greatly accelerate the development and commercialization of non-aqueous RFBs. This Small Business Innovation Research Phase I project aims to develop a novel nanoporous polymer- inorganic composite membrane with high flexibility and controllable sizes of nanopores. This membrane will offer high resistance to swelling, high fouling resistance, high mechanical robustness, high ionic conductivity, and ion selectivity enabled by pore-size exclusion, thus is suitable for application in non-aqueous RFBs. The Phase I work will involve preparation and optimization of the novel nanoporous membrane, and evaluation of the membrane for application in non-aqueous RFBs. The membrane will be systematically characterized in terms of microstructure, chemical stability, swelling resistance, fouling resistance, mechanical durability, and relevant electrochemical properties including ionic conductivity and crossover resistance to redox species. Based on the characterization results, process-structure-property relations will be developed to guide future development. The optimized membrane will be evaluated by non-aqueous RFB performance at the full cell level, including charge-discharge characteristics, cyclability, voltage efficiency, energy efficiency, and lifetime at expected operation conditions. The expected product of the present effort is a low-cost, highly stable, highly ion-selective flexible nanoporous membrane for non-aqueous RFBs. Successful development of this new type of membranes will promote commercialization of non-aqueous RFBs, which will benefit large power storage and high output applications such as for transmission grid operations, in helping to average out the production of highly variable generation sources such as wind or solar power, or in helping generators cope with large surges in demand.