Grid-scale battery storage devices have garnered increased attention for their ability to balance the intermittency of ever-expanding renewable energy deployment and to mediate periods of peak power demand. The redox flow battery has emerged as a viable alternative to traditional solid state batteries. With decoupled electrode and electrolyte storage vessels, the redox flow battery offers design flexibility where capacity and power may be independently tuned. The current state-of-the-art flow battery systems utilize vanadium-based electrolytes, however, the high cost of vanadium has hindered wide-scale deployment.¹ The use of organic molecules as electrolyte materials has emerged as a potentially lower cost alternative.^2,3

Presented will be our recent efforts in developing aqueous-soluble organic molecules as electrolyte materials for redox flow batteries. Structurally related molecules have undergone rational design to affect solubility and redox potential via the introduction of varying substituents on the parent molecule. Promising candidates have been incorporated into a full flow cell and undergone flow cell optimization. An exemplary candidate, when coupled with the benchmark ferri/ferrocyanide catholyte, delivers an OCV of 1.35 V at 50% SOC and achieves stable cycling over extended periods (Figure 1).

References

1. Zhang, M.; Moore, M.; Watson, J.S.; Zawodzinski, T.A.; Counce, R.M. J. Electrochem. Soc. 2012, 159, A1183.
2. Park, M.; Ryu, J.; Wang, W.; Cho, J. Nat. Rev. Mater. 2016, 2, 16080.
3. Soloveichik, G.L. Chem. Rev. 2015, 115, 11533.