Connecting material properties and redox flow cell cycling performance through analytical zero-dimensional models

Improvements in redox flow battery (RFB) performance and durability can be achieved through the development of new active materials, electrolytes, and membranes. While a rich design space exists for emerging materials, complex tradeoffs challenge the articulation of unambiguous target criteria, as the relationships between component selection and cycling performance are multifaceted. Here, we derive analytical solutions for zero-dimensional galvanostatic cell cycling models, enabling direct connections between material / electrolyte properties, cell operating conditions, and resulting performance metrics (e.g., energy efficiency, capacity fade). To demonstrate the utility of this modeling framework, we highlight several representative considerations for RFB design, including upper bound estimation, active species decay, and membrane / separator conductivity-selectivity tradeoffs. We also discuss modalities for extending this analytical framework to incorporate kinetic losses, distributed ohmic losses, and multiple spatial domains. Importantly, because the model is derived analytically, hundreds of cycles can be simulated in seconds, potentially facilitating detailed parametric sweeps, system optimization, and parameter estimation from cycling experiments. More broadly, this approach provides a means for assessing the impact of cell components that simultaneously influence multiple performance-defining processes, aiding in the elucidation of key descriptors and the identification of favorable materials combinations for specific applications.