Full-cycle oxygen-tolerant organic flow batteries

Y.F. Liu, K. Wan, Z.P. Xiang, Z.Y. Fu, Y. Li, M.B. Huang*, Y.C. Lu*, S.D Jiang, Z.X. Liang*

Aqueous organic redox flow batteries (AORFBs) have emerged as a promising candidate for safe and sustainable long-duration energy storage technology. However, the reduced-state species in the negolyte is highly sensitive to oxygen, leading to significant deterioration in both coulombic efficiency and operational stability of AORFBs. Herein, we develop a kinetic strategy to achieve the full-cycle oxygen tolerance of negolyte via the construction of folda-dimer. The folded conformation weakens the electronic coupling between the reduced-state molecule and oxygen, and thus, lowers the observed rate constant by two orders of magnitude compared to monomeric analogues. More importantly, this folded structure formed by intramolecular dimerization endows the system with concentration-independent characteristic, yielding the full-cycle oxygen tolerance. As a demonstration, the flow battery with 1.0 M bis-viologen electrolyte shows a high capacity of 46.5 Ah L^-1, high coulombic efficiency of 99.9% and superior cyclability (capacity retention rate of 99.998% per cycle or 99.96% per day) at 40 mA cm^-2 under air. This study establishes a kinetic stabilization paradigm for developing oxygen-tolerant electroactive organics of the AORFBs.