Redox flow batteries have special advantages for grid energy storage applications because of the unique cell architecture that can decouple the stored energy and power. This has offered excellent scalability and design flexibility to meet different grid requirements. Traditional inorganics-based flow batteries such as all-vanadium are at near-commercialization stage. However, the high chemical cost has led to considerable capital cost that great limits their broad market penetration. On the other hand, some redox-active aqueous soluble organic (ASO) materials can offer significant cost and performance merits and enable competitive flow battery systems.^1,2Facile molecular diversity and structural tailorability also gain benefits in achieving high solubilities and cell voltages for flow batteries.

Here we report our materials developmental accomplishments in pursuing high-performance ASO flow batteries.³A variety of promising ASO candidates have been identified with desirable redox potentials and kinetics. Our strategies to improve the solubilities, chemical stabilities, and system performance of these ASO materials will be discussed. We also have gained fundamental understandings of the key performance-limiting factors in determining chemical stability of these redox species and capacity degradation of flow systems. These insights can effectively guide future ASO materials development and improvement.

References

1. Winsberg, J.; Hagemann, T.; Janoschka, T.; Hager, M. D.; Schubert, U. S. Angew. Chem. Int. Ed. 2017, 56, 686 –711.

2. Park, M.; Ryu, J.; Wang, W.; Cho, J. Nat. Rev. Mater. 2016, 2, 16080.

3. Liu, T.; Wei, X.; Nie, Z.; Sprenkle, V.; Wang, W. Adv. Energy Mater. 2016, 6, 1501449.

Figure 1. The stable cycling efficiencies and capacities of an ASO flow battery.