Modelling electrolyte transport and crossover within redox flow batteries

Renewable energy sources, such as wind and solar, generally suffer from intermittency issues. This necessitates systems that store energy whilst supply is high and demand is low. Many prospective technologies are electrochemical and store energy by converting reactants within an electrolyte at the surface of an electrode.

This includes redox flow batteries, whose novelty lies in the fact that the electrolyte is pumped into the reaction chamber - raising questions about the influence of a flowing electrolyte on the transport of mass within the chamber. Furthermore, flow batteries are limited by a phenomenon called species crossover, whereby reactants permeate the membrane that separates the two reaction chambers.

This can lead to poor coulombic efficiency (for symmetric chemistries) and even capacity loss (for asymmetric chemistries). A better understanding of the relationship between flow and crossover is needed to identify reactor designs or control schemes that mitigate this unwanted process.

For this project, our aim is to conduct a rigorous theoretical investigation into electrolyte transport within multi-component electrochemical systems, and, in particular, explore the effects of advection, which are overlooked in most standard battery models (for example of the Doyle-Fuller-Newman type). Solving this problem in a flow battery presents an especially complex challenge and for that reason, we propose to first establish a framework that can solve electrolyte transport within simpler systems.

This will still provide a novel research challenge, as current models neglect phenomena like 'faradaic convection' (flow induced by interfacial electrochemical reactions) and viscous flow driven by electrolyte-density gradients. Finite-element methods will likely be required to approach this challenge. A thorough theoretical understanding of the physics dictating transport within electrochemical systems would be a valuable tool for a variety of energy storage industries (electrolyzers etc.) and provide a solid foundation to model more complex systems, such as the redox flow battery.

This may also lead to the identification of optimal flow field designs (the geometry of the channels in which the electrolyte is pumped through the chamber), which is a component of the battery ripe for innovation. There is presently very little theoretical understanding of how the design of these channels affects transport within a flow-battery reaction chamber.

This project falls within the EPSRC Energy Storage area.