PNNL

Abstract

Aqueous organic redox flow batteries hold great promise as a technology for creating economical grid energy storage using sustainable materials. Nonetheless, the solubility limit presents a universal barrier for all redox-active organic molecules. In this paper, we propose and explore a new approach to surpassing the solubility limit by manipulating the solvation structure with polycomplex ion additives. Using the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as an example, we investigate its role in dismantling the rigid supramolecular clusters within the highly concentrated 7,8-dihydroxyphenazine-2-sulfonic acid electrolyte. 1H and 23Na nuclear magnetic resonance spectra and molecular dynamics simulation studies demonstrate that the bi-polar structure of the PIA effectively disrupts the aggregations of DHPS and Na+ ion in the highly concentrated DHPS electrolyte, thus rendering a more flexible solvation structure and less restrictive ion transport, leading to substantially improved solubility, rate capability, and stable cycling stability in an AORFB cell. The DHPS electrolyte with PIA additive achieved 1.6M, ~15% higher than its saturation concentration, and 74.3 Ah L-1 energy capacity, one of the highest demonstrated among all the organic flow batteries. This study introduces a novel approach to overcome the solubility limit of organic active molecules by intentionally manipulating the solvation structure.