KES6-0433
Next-generation Organic Redox Flow Batteries for Grid Integration
Topic
S6. Emerging Polymer and Hybrid Materials for Advanced Energy Storage and Conversion
When and Where
Sep 30, 2026
15:25 - 15:50
Room 311 & 312
Session Chairs
Wonho LEE
Presenter(s)
Kenichi Oyaizu (Waseda University)
Co-Author(s)
Abstract
An organic redox flow battery uses organic redox-active molecules dissolved or dispersed in aqueous electrolyte solutions, stored in tanks and pumped to a cell equipped with a current collector and a separator. In addition to low-molecular-weight organic molecules, organic polymers are also investigated taking advantage of their inherent properties such as suppressed crossover across lower-cost nanoporous separators than the expensive ionic exchange membranes currently used. Two challenges have emerged thus far: increasing the polymer concentration to boost energy density also increases viscosity, resulting in higher flow energy losses; and the solubility of the polymer in the aqueous electrolyte solution limits volumetric energy density. We found that a novel redox polyelectrolyte approach could solve these issues and lead to a flow battery with higher energy density and excellent cycle performance. A typical example of the redox polyelectrolyte is poly(N-(3-acrylamidopropyl)-N,N,2,2,6,6-hexamethylpiperidinyloxy-4-aminium) bearing an ammonium group to bind TEMPO and acrylamide within each repeating unit. The polyelectrolyte dissolved in a 1 M NaCl solution at more than 54 Ah/L while maintaining flowability. The permeability of the polyelectrolyte (Mn = ca. 20000) across a porous dialysis membrane with MWCO = 3500 was less than 1/1000 that of the monomeric analog, 4-trimethylammonio-TEMPO chloride, suggesting that the polyelectrolyte is a candidate for the catholyte with the conventional vanadium-class high capacity. Interestingly, the polyelectrolyte exhibited a decrease in intrinsic viscosity when oxidized (or charged) to the oxoammonium-substituted polymer. The molecular weight dependence of the intrinsic viscosity revealed that the reduction in viscosity is primarily due to the contraction in volume of the hydration shell, rather than the effect of increased rigidity resulting from the oxidized polyelectrolyte's increased charge.
