Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources. With the goal of cost-effective, safe, and scalable stationary electricity storage systems, AORFBs could eclipse Li-ion batteries due to their inherent non-flammability, lack of materials scarcity fluctuations, and intrinsic decoupling of energy and power capacities. We have previously demonstrated that calendar life, rather than cycle life, limits molecular lifetimes in AORFBs due to various molecular instabilities that lead to side reactions, thus inhibiting performance [1]. The continued synthetic effort to produce stable redox-active organics has improved molecular design strategies to the point that the most stable chemistries now degrade at less than 1% per year [2].

With further lifetime increases, the measurement of lower capacity fade rates now necessitates higher precision coulometry methods [3] and the use of thermally accelerated decomposition protocols [4,5] to determine which stabilizing approaches are most effective without waiting for multi-month cycling tests to quantify capacity fade.

In this presentation, I highlight a high-throughput setup we have recently developed for the electrochemical screening of candidate molecules in AORFBs. We demonstrate the effect that cycling protocols can have on measured capacity fade rates and propose figures of merit for cell-to-cell variability. Finally, we explore accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime AORFBs, which may enable massive grid penetration of intermittent renewable energy.

[1] M.-A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods,” Journal of The Electrochemical Society, 165, A1466 (2018).

[2] M. Wu, Y. Jing, A. A. Wong, E. M. Fell, S. Jin, Z. Tang, R. G. Gordon, M. J. Aziz, “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors,” Chem, 6, 1432 (2020).

[3] T. M. Bond, J. C. Burns, D. A. Stevens, H. M. Dahn, and J. R. Dahn, "Improving Precision and Accuracy in Coulombic Efficiency Measurements of Li-Ion Batteries,” Journal of The Electrochemical Society, 160, A521 (2013).

[4] D. G. Kwabi, K. Lin, Y. Ji, E. F. Kerr, M.-A. Goulet, D. De Porcellinis, D. P. Tabor, D. A. Pollack, A. Aspuru-Guzik, R. G. Gordon, and M. J. Aziz, “Alkaline Quinone Flow Battery with Long Lifetime at pH 12,” Joule, 2, 1894 (2018).

[5] D. A. Stevens, R. Y. Ying, R. Fathi, J. N. Reimers, J. E. Harlow, and J. R. Dahn, "Using High Precision Coulometry Measurements to Compare the Degradation Mechanisms of NMC/LMO and NMC-Only Automotive Scale Pouch Cells,” Journal of The Electrochemical Society, 161, A1364 (2014).