(307f) Establishing Design Principles for Redox Flow Batteries with Suspension-Based Electrolytes

Redox flow batteries (RFBs) are an electrochemical platform that may further global decarbonization efforts by offsetting the intermittency of electricity generation from renewable energy resources. The system possesses several enabling features, including independent scaling of power and energy, long operational lifetimes, and simplified manufacturing which together offer a pathway to cost-effective grid-scale energy storage. In conventional RFBs, charge is stored using redox couples dissolved in liquid electrolytes and circulated between an electrochemical reactor and storage tanks. Active species solubility limits the energy density for this architecture. The introduction of suspended solid particles for charge storage and conduction is an emerging trend that may enable increased energy density (smaller system footprint) and higher volumetric surface area for faradaic reactions (high power). However, suspension-based electrolytes exhibit complex rheological and electrochemical behavior under flow, which challenge the design and operation of high-performance RFBs. Further, the interplay between electrochemistry, transport, and rheology within these electrolytes is poorly understood, especially under the dynamic conditions associated with flow-based electrochemical devices.^[1-4]

In this talk, we present a one-dimensional model integrating electrochemistry, charge transport, and non-Newtonian rheology to establish design principles for RFBs with suspension-based electrolytes. Specifically, this model combines Butler-Volmer reaction kinetics at the particle-electrolyte interfaces, Ohm’s law for the electronic and ionic phases, charge conservation in the bulk, mass transport descriptions across the boundary layers around the suspension particles, and non-Newtonian rheological models to form a compact set of governing equations. We then derive key dimensionless groups whose relative magnitudes determine the impact of different physical processes on cell behavior. We solve the model for different dynamic and geometric constraints to identify operating regimes, to compute tradeoffs between cell power output and suspension pumping power input, and, ultimately, to establish favorable materials sets and operating envelopes. More broadly, the general modeling framework presented here will aid in establishing design rules for electrochemical systems with suspension-based electrolytes that extend beyond RFBs (e.g., separation, desalination, electrosynthesis).

Acknowledgments

This work was funded by the Skoltech – MIT Next Generation Program.

References

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