Catholyte Development for Non-Aqueous Redox Flow Batteries

Non-aqueous redox flow battery is a promising large scale stationary energy storage technology. Unlike traditional battery systems, the active energy storage material is in mobile phase and stored in external tanks. The energy and power of RFBs thus can be decoupled and independently scaled, which offers remarkable design flexibility for applications with various energy-to-power ratios.

Material development for this technology is crucial for practical implementation. Molecular engineer of organic redox active molecules could lead to tunable physical and electrochemical properties, including solubility in organic solvents, molecular mobility, redox potential, and electrochemical reversibility, which are key factors to energy storage applications. The dimethoxybenzene based catholyte molecules have been systematically developed and evaluated towards various purposes. For instance, ANL-8, ANL-9 and ANL-10 molecules were developed by incorporation of PEO chains with different lengths on one or both sides of the dimethoxy-di-tert-butyl-benzene based redox structure in order to afford higher solubility. Another category of the molecules, including JH-100 and JH-200, were developed by striping down the non-essential structures, such as tert-butyl groups and ether chains, in order to boost the intrinsic capacities. While many of these molecules can afford electrochemically reversible behavior, some new promising features are discovered. ANL-8 and ANL-9 molecules are found to be liquid at room temperature, which was hoped to function as co-solvent for NRFBs, thus leading to much improved energy density. JH-100 and JH-200 molecules, on the other hand, offer much enhanced intrinsic capacity (nearly two times as big as DBBB), which also is believed to be a key to further improve the energy density and lower the cost of NRFBs.