Physics‐Based Transmission Line Model for Explanation of Electrochemical Impedance Spectroscopy Spectra of Vanadium‐Based Flow Batteries

Existing models describing the impedance response of vanadium flow batteries typically use a bottom‐up approach, incrementally adding complexity to simple mathematical descriptions to account for missing transport processes. In this study, we present a reverse, top‐down approach by developing a physics‐based transmission line model that is general, customizable, and that can be ultimately simplified to a single equation for the studied electrochemical system. The model incorporates transport through the ion‐selective membrane, electrolyte‐filled pores, and diffusion layer, as well as the reaction at the electrode interface, electronic conductivity of the carbon felt, and contact resistances. This model enables a universal description of flow battery impedance response, which can help identify bottleneck processes and guide improvements in next‐generation battery design.