The energy density of conventional redox flow batteries (RFBs) is dictated by their capacity (which is directly related to the solubility of the redox species in the electrolyte) and operating potential. RFBs have low operating potentials ca. 1.5 V, resulting in poor energy densities (25 – 30 Wh/kg for an all vanadium RFB), whereas systems containing organic electrolytes with wider electrochemical windows can potentially have moderately higher energy densities. A new approach to improve the performance of nonaqueous redox flow batteries (RFBs) through electrochemically-mediated reactions is demonstrated. Soluble anion radical species (biphenyl and pyrene) mediate reversible sodium storage in a red phosphorus anode located in an external plug flow reactor in the absence of binders or conductive additives. Because the anion radical species can be recycled several times throughout the cell stack during a single charge/discharge cycle, a mediated RFB effectively decouples the battery’s energy density from the redox species’ solubility in the electrolyte. Furthermore, this technology offers inherently safe operation and is unaffected by the large volume changes of red P (>300%) due to the use of an external plug flow reactor. This presentation will describe the mechanism of a mediated RFB and discuss important design considerations (e.g., selection of appropriate electrolyte, mediators, active materials, etc.). Results showing electrochemically mediated sodiation and desodiation of a phosphorus anode in a redox flow configuration will be presented

This work is supported by Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy and The Office of Electricity Delivery and Reliability, U. S. Department of Energy.