Realization of an Asymmetric Non‐Aqueous Redox Flow Battery through Molecular Design to Minimize Active Species Crossover and Decomposition
Anuska Shrestha, Koen H. Hendriks, Mathew S. Sigman, Shelley D. Minteer, Melanie S. Sanford
Abstract
This communication presents a mechanism-based approach to identify organic electrolytes for non-aqueous redox flow batteries (RFBs). Symmetrical flow cell cycling of a pyridinium anolyte and a cyclopropenium catholyte resulted in extensive capacity fade due to competing decomposition of the pyridinium species. Characterization of this decomposition pathway enabled the rational design of next-generation anolyte/catholyte pairs with dramatically enhanced cycling performance. Three factors were identified as critical for slowing capacity fade: (1) separating the anolyte-catholyte in an asymmetric flow cell using an anion exchange membrane (AEM); (2) moving from monomeric to oligomeric electrolytes to limit crossover through the AEM; and (3) removing the basic carbonyl moiety from the anolyte to slow the protonation-induced decomposition pathway. Ultimately, these modifications led to a novel anolyte-catholyte pair that can be cycled in an AEM-separated asymmetric RFB for 96 h with >95 % capacity retention at an open circuit voltage of 1.57 V.