Prospect of Modeling Industrial Scale Flow Batteries – from Experimental Data to Accurate Overpotential Indentification
55 Pages Posted: 15 Mar 2022
Abstract
A vast literature exists on modelling of small-scale single-cell experiments for flow batteries, but very few reports have been published on large stacks, consisting of tens of cells, each with an active area of hundred square centimetres. In this report, a large set of measurements taken on the kW-class vanadium test facility is used to develop an accurate ad-hoc physical model. Experimental data consists of polarization curves at a broad range of states of charge and electrolyte flow rates and electrochemical impedance spectra. The developed model is capable to decouple three main sources of voltage losses: activation, ohmic and concentration overpotentials. In addition, a new approach for determinating the main parameters of the internal processes related to electrochemical kinetics and mass-transport limitations has been proposed. The approach uses numerical identification procedures of the model parameters. To the best of our knowledge, this is the first time a model for voltage losses analyses was developed and fitted to the data from a large-scale VRFB by means of an identification procedure, being validated with a sensitivity analysis study. Investigations showed that activation losses play an important role in every operating condition and not only at the low current density, as usually reported, so that they must be included in a reliable model. This work also highlights that, in the investigated case, activation losses are likely to be attributed to the positive electrode rather than to the negative one. The obtained results may support the simulation and design of advanced flow battery stacks.
Keywords: Redox-flow battery, Performance model, Polarization curve, Model identification, Electrochemical kinetics, Numerical modelling
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