Redox flow batteries have been considered as one of the most promising grid energy storage technologies. The unique cell architecture leads to an important advantage of decoupled energy and power, which offers very flexible designs and excellent scalability to meet different grid applications. State-of-the-art flow batteries based on inorganic redox-active materials (e.g. vanadium) have gained significant momentum and even commercialization offerings. However, the broad market penetration is hampered by limited energy density and/or high cost. This has driven the search for electrochemically active, cost-effective aqueous soluble organics (ASO) to enable competitive flow battery systems. Organic compounds have other advantages of molecular diversity and structural tailorability to enable high solubilities and desirable cell voltages.

Here we report the new development of high-performance ASO flow batteries at Pacific Northwest National Laboratory.¹Materials discovery efforts have led to identification of promising ASO candidates, followed by structural tailoring to improve the solubilities, redox activity, and chemical stability. Electrolyte engineering was also carried out to improve the rate performance and cyclability of the ASO flow batteries. Finally, systematic spectroscopic analysis has revealed the mechanisms of capacity fading observed in these ASO flow batteries.

References

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

Figure 1. The ASO flow battery based on methyl viologen (MV) and 4-hydroxy-TEMPO (TEMPOL). The mechanistic studies of capacity fading will be discussed.