The soluble lead flow battery: numerical modelling for enhanced design of cell architecture

Abstract

This thesis describes a two-dimensional numerical model, based on the conservation of mass, charge, momentum and energy, and the main electrode reactions and a single simplified side reaction and their kinetics for the soluble lead flow battery (SLFB). The model is developed to include a change in morphology as solid deposits form at the electrode, on both flat planar electrodes and porous carbon foam electrodes, and to include a framework for modelling the anion- cation-exchange membrane and separator divided SLFB along with a semi-empirical method to predict electrolyte conductivity at different electrolyte concentrations. All models are validated against experimental work presented in this thesis or from the literature. The change in morphology on flat electrodes leads to a significant decrease in distance between the electrode surfaces causing a reduction in cell resistance and a decrease in volumetric electrolyte flow. This approach could be easily adapted for any battery with a metal/metal ion electrode reaction. Anion exchange membranes were found to have a reduced potential drop at low states of charge but an increased potential drop at high states of charge when compared to cation exchange membranes. Porous separators were found to have an order of magnitude lower potential drops for separators of the same thickness. However, they do not provide any selectivity for electrolyte additives. A method of manipulating computed tomography images of reticulated vitreous carbon electrodes (RVC), using a voxel dilation technique to simulate the deposition of Pb and PbO2 at various states of charge are converted to homogeneous electrode domains for use in the numerical model of the SLFB. It is shown that the current distribution in the domain varies at different states of charge both perpendicular and parallel to the electrodes. However, adding a porous separator in place of a free electrolyte domain to divide the electrode domains mitigates this variation, especially along the length of the electrodes. An improved voltage efficiency of over 80 % is seen when RVC electrodes are used.

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Identifiers

ORCID for Ewan, Joseph Fraser: orcid.org/0000-0001-9592-9071

ORCID for Richard Wills: orcid.org/0000-0002-4805-7589

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