Development of membrane separators is important to decrease cross-over and enhance efficiency and durability of non-aqueous redox flow batteries. Desired properties of the membranes for the application include (a) selective ion permeability, (b) high conductivity and (c) good chemical and mechanical stability in operating conditions of redox flow batteries. Our approach to satisfy these criteria is synthesizing cation-functionalized nitrile-containing polyaromatics, poly(arylene ether benzonitrile)s, for membrane separators. While these membranes exhibited good performances in an aqueous vanadium redox flow battery (VRFB) system, in non-aqueous systems where acetonitrile is used as electrolytes, the membranes could not be utilized due to their limited mechanical strength. To endure the harsh operating condition of non-aqueous VRFB, we developed crosslinked quaternized poly(arylene ether benzonitrile)s. A series of high molecular weight polymers with tertiary amine groups were synthesized via aromatic nucleophilic substitution polycondensation followed by the simultaneous quaternization and crosslinking reactions. In this presentation we will discuss the membrane properties and the electrochemical performance of these membranes in terms of cycling efficiencies, vanadium permeation and membrane durability. The applicability of crosslinked quaternized poly(arylene ether benzonitrile) membranes in non-aqueous VRFB systems will be summarized.

Acknowledgement

This work is fully supported by Laboratory Directed Research & Development, Los Alamos National Laboratory.

The submission of the manuscript is approved by LANL (LA-UR-19-23557)