Understanding Characteristic Electrochemical Impedance Spectra of Redox Flow Batteries with Multiphysics Modelling

Abstract Electrochemical impedance spectroscopy (EIS) is a non-destructive technique for analyzing electrochemical systems (such as redox flow batteries – RFBs). Battery researchers widely adopt equivalent circuit models (ECMs) to analyze EIS spectra of RFBs and attempt to use the circuit to deduce prevalent transport and kinetic properties [1]. Straightforward adoption of these ECMs suffers from some setbacks which need rectifying. There is a major issue of poor or inconsistent physical interpretation of the different circuit elements. ECMs of batteries are commonly used in real-time applications due to their simplicity and importance for determining properties like state-of-charge. However, prediction performance in low state-of-charge areas has to be improved [2], which reinforces the need to relate recorded spectra to the physical properties of cell components. Using an experimentally validated full Multiphysics model of single-cell vanadium RFB analyzed in the frequency domain, we approach understanding the EIS spectra characteristics based on the influence of cell features and operating parameters. To achieve our analyses, we investigate the effects of different cell properties and operating parameters on the Multiphysics model produced EIS spectra and the resulting ECM circuit element parameters that fit the spectra. Five different values for each cell property or operating parameter are considered for the following components: Electrode: Electrical conductivity, porosity vis a vie specific surface area and hydraulic permeability, reaction rate constants for the positive and negative sides. Membrane: Ionic conductivity, fixed charge concentration, porosity, and hydraulic permeability. Electrolyte: State-of-charge, Composition vis a vie bulk diffusion coefficients of species, density, and viscosity. References [1] A.K. Tripathi, D. Choudhury, M.E. Joy, M.J.J.o.T.E.S. Neergat, Electrochemical Impedance Spectroscopic Investigation of Vanadium Redox Flow Battery, 169 (2022) 050513. [2] Y.A. Gandomi, D. Aaron, T. Zawodzinski, M.J.J.o.T.E.S. Mench, In situ potential distribution measurement and validated model for all-vanadium redox flow battery, 163 (2015) A5188.