An Open Circuit Voltage and Overpotential Model for an All Vanadium Redox Flow Battery Derived from Several Years of Operating Data

Abstract

One essential part in the simulation of electrochemical storage systems like redox flow batteries is the voltage on cell level. In this study, a model is derived for the open circuit voltage and the overpotentials of an all Vanadium system, based on the operation data of three commercial batteries over an extended period. The high amount of observations, especially the combination of a wide range of electrolyte temperatures and currents at different states of charge, allows for the correct identification and modelling of the relations between voltage and the measured variables. Different variants of Nernst equations are evaluated and it is found that considering temperature dependent standard electrode potentials and the inclusion of proton concentration in the catholyte are vital. Three types of overpotentials are modelled and respective parameters defining mass and charge transport are derived from the experimental data. Keywords—all Vanadium redox flow, electrochemical storage, simulation, voltage model, open circuit voltage, overpotential