Toward High-Voltage, Energy-Dense, and Durable Aqueous Organic Redox Flow Batteries: Role of the Supporting Electrolytes

Sustainable energy supply from renewable sources requires highly efficient and economically competitive energy-storage technologies. With flexible design, high energy-storage efficiency, and long-term cyclability, redox flow batteries are superior candidates for peak shaving and load leveling for smart grids in the energy generation, storage and distribution networks. With natural abundance, structural diversity and tunability, redox-active organic species as valuable alternatives to the traditional inorganic-based materials are promising to tackle the resource and performance limitations. To design aqueous organic redox flow batteries toward energy-dense, high-rate performance and durability, in this Review, strategies to maximize the cell voltage, effective concentration of organic species, and operating current density are discussed. Besides the inherent nature of the organic molecules, suitable solvents and supporting ions can affect their solvation behavior and promote their chemical stability.