Exploring Performance Tradeoffs in Redox-mediated Flow Batteries

Redox-mediated flow batteries (RMFBs), an emerging subclass of redox flow batteries (RFBs), incorporate solid active materials into the tanks to dramatically increase theoretical energy density, albeit currently at the expense of design and operational simplicity. Using physics-based models, we assess the performance tradeoffs inherent to these systems, with an emphasis on understanding what factors most impact accessible power and energy densities and how this new concept compares to conventional RFBs. Through sensitivity analyses and sampling methods, we identify key dimensionless parameters with the greatest influence on system capacity (e.g., Damköhler numbers and dimensionless current) and reveal a “collapsed relationship” that effectively captures the predicted solid utilization. We assess the distinct tradeoffs in cell power, pumping losses, and solid utilization associated with RMFBs, by tuning physical and operating parameters (e.g., particle size and current). Ultimately, we identify favorable property profiles that enable desirable power and energy characteristics. Finally, we reflect on the implications of these analyses, translating the model-based findings into engineering guidance and intuition on the relative merits of single- versus dual-mediator systems, on the general importance of mediator concentration for power density, and on design strategies to balance electrochemical and fluid dynamic performance.