Achieving Consistency in Redox Flow Battery Power Characterization: Methodologic Insights

Power characterization of redox flow batteries (RFBs) is predominantly conducted in scientific literature using polarization curve analysis.The characteristics of RFBs necessitate a consistent methodology for RFB cell/stack power characterization and rating, facilitating direct performance comparisons across different systems.This work explores constant-current polarization and constant-power methods for assessing RFB power in literature and relevant industrial standards.Unfortunately, there are vast differences in published literature towards measurement of the same metric (RFB cell/stack power), which hinder comparison.We apply numerical and Multiphysics modeling to define a recommended polarization step duration corresponding to prevalent time constants where RFB test cells/stacks attain quasi-steady-state response of potential and outflow state-of-charge (SOC) under constant-current polarization.Although the recommended duration is defined with an idealized tank system, this time constant can also be imposed on real tank systems, provided the half-cell volume to total electrolyte volume ratio (per side) is low enough (like 1:25), while ensuring proper tank stirring.Our experimental validations with a kW-scale commercial stack reinforce the validity of the models, simulation framework, and accompanying simplifying assumptions.We subsequently outline a proposed protocol to ensure consistency and standardized net power characterization/rating using constant-current discharge polarization tests on RFB cells/stacks.