Assessing and Modifying Selective Transport for Nonaqueous Flow Battery Membranes

Abstract

Membranes are a critical component for redox flow battery (RFB) systems. An ideal membrane must be stable in the RFB solvent and process environment, and to obtain desirable electrochemical performance must facilitate transport of the charge compensating ion while minimizing crossover of the dissolved electroactive species (e.g., redox shuttles). For more established aqueous RFB systems commercial membranes, such as sulfonated fluoropolymers, have been used to successfully facilitate development of RFB power stacks at industrial scales.Recently, there has been interest in developing nonaqueous, or organic, RFB systems. A potential advantage of a nonaqueous RFB is the accessibility of higher voltages per cell, which would result in higher energy density for the RFB system. Membrane materials for nonaqueous RFBs are not well established, and thus the composition and processing for these membranes is an open area for further research.In this talk, efforts towards the understanding and development of a nonaqueous RFB membrane material will be described. Assessment of the conductivity and crossover of the membrane material system will be discussed, as well as efforts to improve electrochemical properties and membrane stability. Initial results suggest that the interactions between the redox shuttles and the membrane are in many cases fundamentally very different for nonaqueous RFB membranes compared to aqueous RFB membranes, providing possibilities for different routes to design nonaqueous RFB membrane materials.