Strategies for Improving Solubility of Redox-Active Organic Species in Aqueous Redox Flow Batteries: A Review

Redox flow batteries (RFB) have emerged as one of the most promising technologies for large-scale energy storage owing to their high safety, long operation life, and decoupled design of energy and power. However, the problems of high cost and low energy density restrict their further development. The cost merit and tunable structure of organic redox-active materials have prompted the development of organic RFBs. The solubility of the redoxmer is recognized as a parameter that contributes directly to the energy density. Herein, we focus on strategies for enhancing the solubility of organic redoxmers in aqueous RFBs. The effects of incorporating different hydrophilic functional groups on the solubility of the redoxmer and its effect on the performance of other batteries are systematically and exhaustively described. Other strategies, such as molecular symmetry tuning and employing more soluble counterions and cosolvents, are also summarized. The development trends and prospects for organic RFBs are also discussed.

Automated summary

Redox flow batteries (RFB) are considered as one of the most promising technologies for large-scale energy storage due to their high safety, long life and decoupled energy and power design. However, the high cost and low energy density limit further development. The development of organic RFBs is driven by the cost advantage and tunable structure of organic redox-active materials. Solubility is recognized as one of the parameters that directly affect energy density.