Robust Simulation of Coupled Reactions and Transport in Redox Flow Batteries Using Tailored Numerical Schemes

Abstract

Redox flow batteries (RFBs) are attractive energy storage solutions for the grid, the simulation of which enables system and material optimization. In this article, we introduce tailored numerical schemes to model coupling between the transport of dissolved species, electrons, and fluid with redox reaction kinetics within RFBs in a robust way. The macro-scale transport of species (including advection, migration, and hydrodynamic dispersion) is coupled with the volume-averaged pore-scale processes of reaction kinetics, and mass transport, while the Poisson equation is used to model Donnan exclusion across ion exchange membranes that limit capacity fade due to the crossover of redox-active species. The governing equations are discretized using the finite volume method with a Newton-Raphson iteration scheme to resolve non-linearity. We introduce several numerical schemes to increase solver robustness, including reaction rate damping and logarithmic transform of concentration fields. Based on fixed-point iteration convergence criteria we also show that the mechanistic Marcus-Hush-Chidsey (MHC) redox kinetics model can tolerate larger time steps than the empirical Butler-Volmer (BV) kinetics model. The numerical schemes presented in this article can also find application in other electrochemical systems, including desalination devices, fuel cells, and electrodialysis.