Pentablock Copolymer Membranes for Non-Aqueous Redox Flow Batteries

Abstract

Long duration energy storage devices, such as redox flow batteries, are needed to enable smart grids and widespread adoption of renewable energy sources. Sodium based electrochemical energy storage is of interest for large-scale applications due to sodium’s low cost and high abundance compared to lithium and vanadium. The membrane plays a critical role in flow batteries by providing counterion transport while separating the catholyte and anolyte. Considering that the membrane is a significant source of internal resistance and capacity fade (e.g., due to crossover) in an operating battery, developing membranes with controlled swelling, high ionic conductivity, and low active species crossover is imperative. In this work, we studied electrolyte uptake and ion transport in cation exchange pentablock copolymer membranes with sodium sulfonate and sodium trifluoromethanesulfonimide (TFSI) functionality for nonaqueous flow battery applications. The TFSI Na membranes exhibit an ionic conductivity of 7.2 x 10-5 S/cm at room temperature and a cation transport number of 0.75 in 0.5 M sodium triflate/tetraethylene glycol dimethyl ether (TEGDME) electrolyte. Methods improve the ionic conductivity and limit electrolyte uptake of the membranes, such as crosslinking will be discussed. Acknowledgements This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program in the Office of Electricity.