Parametric Modelling of a Non-Aqueous Redox Flow Battery with Solid Booster Materials
Authors: Hoene Henning , Cappillino Patrick J. , Agar Ertan , Jin Xinfang 
Published: September 2023

With an increasing use of renewable energy resources, such as wind and solar, one of the major challenges that need to be addressed is the energy reliability associated with the intermittent nature of these resources. Redox flow batteries (RFBs), which are considered as a promising large-scale energy storage technology, have the potential to address this issue due to their enhanced capacity retention, ease of scalability, and cost-effectiveness in long-duration energy storage [1]. Despite the promise, the widespread implementation of RFBs is currently hindered by their lower energy density compared to lithium-ion batteries and hydrogen energy storage [2].

Non-aqueous redox flow batteries (NRFBs) offer volumetric energy density improvement by increasing the electrochemical potential window. While the idea of non-aqueous systems is not new in concept, they have become more prevalent and very few models have been described in literature [3]. In this study, a mathematical model of a NRFB using a bio-inspired active material, vanadium(iv/v) bis-hydroxyiminodiacetate (VBH) [4] is developed. To further increase the energy density of the system, a solid capacity booster material, cobalt hexacyanoferrate, is introduced into the electrolyte tanks. The solid booster increases the electrolyte capacity by chemically reacting with the redox active material in the tank [5]. Since the inclusion of solid booster materials is a relatively novel concept for RFBs, few resources are available, and to the best of our knowledge, no model has yet to be presented for a solid booster system [6].

The mathematical model is developed with charge and species conservation using the Nernst-Planck equation. Then, the model is validated with an experimental charge/discharge curve without solid booster material. The solid booster concept is included by incorporating the shrinking core model and Gibbs free energy [7]. Using the model developed, sensitivity and correlation analyses are conducted to identify independent parameters associated with the solid booster material. Lastly, the charge/discharge experimental data with the solid booster material is fitted to the model prediction to identify the thermodynamic and kinetic parameters of the indirect chemical reaction that occurs in the tanks. The development of this model can provide insights for future studies utilizing solid boosters in redox flow batteries and help identify key parameters affecting the performance of these systems.

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