Nonaqueous redox flow batteries are often limited by the solubility of the redox active species, constraining the maximum energy density. One route to increasing the energy density is through chemical mediation of solid energy-storing materials, such as common Li-ion battery anodes and cathodes. These solid energy-storing materials can be contained in canisters through which an electrolyte with redox active species (mediators) is flowed in typical flow battery fashion. The redox potentials of the flowing species are chosen to mediate the chemical reduction and oxidation of the solid energy-storing materials. Afterwards, the mediators are recharged in the electrochemical cell. This strategy is advantageous in that it allows for independent optimization of the flowing electrolyte (e.g. for low viscosity, high discharging rates) and the solid energy-storing media (e.g. for high energy density). We demonstrate application of this strategy to some common Li-ion battery materials and show how choice of membrane and mediator influences overall cell performance in terms of efficiencies and capacity fade. Optimization of this mediated system’s parameters promises flexible, high density energy storage for nonaqueous redox flow battery systems.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.