Develop Low-cost Membranes for non-aqueous Redox-flow Batteries

G. Yang, M. Lehmann, E. Self, R. Sacci, T. Saito, J. Nanda
Oak Ridge National Laboratory,
United States

Keywords: redox flow battery, membrane, long-duration energy storage


Develop Low-cost Membranes for non-aqueous Redox-flow Batteries Guang Yang1, Michelle Lehmann1, Ethan Self1, Robert Sacci1, Tomonori Saito1, and Jagjit Nanda2 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States Abstract Penetration of intermittent energy storage requires developing long-duration energy storage (LDES) systems, such as solar and wind into the electric grid. DOE’s Long Duration Storage Shot establishes an ambitious target to reduce the cost of grid-scale energy storage by 90% for systems with durations of >10 hours. Non-aqueous redox-flow batteries (nRFB) using earth-abundant materials (such as sodium and sulfur) are promising to fulfill this target. However, a key bottleneck to keeping RFB from market penetration is the lack of high-performance and cost-effective membranes. Membranes represent the most critical component in non-aqueous RFB, and they play a decisive role in cell stack performance and overall cost. Herein, we present recent progress on the membrane development for the non-aqueous flow batteries. The ionic conductivity - mechanical strength tradeoff is a long-standing challenge for all polymer electrolyte development. In a redox flow battery, solvent uptake promotes membrane ionic conductivity but decreases its storage modulus due to the increased polymer chain relaxation. Two strategies are found effective to alleviate such tradeoff i) selective plasticization of the ion-conductive block in a block copolymer membrane, such as poly(ethylene oxide) (PEO) in a polystyrene (PS)− PEO−PS block copolymer (SEO) electroconductivity by an ether type solvent, and ii) enhancement of the membrane mechanical strength by creating hydrogen and ionic bonds between the polymer matrix and the inorganic scaffold. Mitigating redox-active species crossover poses another challenge in membrane design. We show that the cation-exchanged single ion conducting membrane can effectively decrease the crossover of the polysulfide species in a Na metal – polysulfide hybrid flow battery, which promotes the RFB capacity retention, Columbia efficiency, and cycle life benchmarked to a commercial porous membrane. Acknowledgment This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy and is sponsored by the U.S. Department of Energy in the Office of Electricity through the Energy Storage Research Program, managed by Dr. Imre Gyuk.