Liquid Nitrobenzene-Based Anolyte Materials for High-Current and -Energy-Density Nonaqueous Redox Flow Batteries

Nonaqueous redox flow batteries (NARFBs) are a potential candidate for high-energy-density storage systems because of their wider electrochemical windows than that of the aqueous systems. However, their further development is hindered by the low solubility of organic redox-active materials and poor high-current operations. Herein, we report a liquid anolyte material, 3-nitrotoluene (3-NT), which demonstrates high chemical stability and mass- and charge-transfer kinetics. The NARFB based on 2,5-di-tert-butyl-1-methoxy-4-[2'-methoxyethoxy]benzene/3-NT exhibits an energy efficiency of 71.8% even at a relatively high current density of 60 mA cm^-2. Benefiting from the high miscibility of the redox species, an ultra-high volumetric energy density of 37.8 W h L^-1 can be achieved at 1.0 M. This work provides a viable method to build an NARFB with both high operational current density and energy density for next-generation, low-cost, and high-energy storage systems.