Improvements to the soluble lead redox flow battery

Abstract

Redox flow batteries are energy storage devices that have successfully been commercialised and demonstrated on the MW/MWh scale for various power applications, such as renewables capacity firming. The vanadium and zinc-bromine systems, having been developed over several decades, are currently the most advanced. However, their respective limitations have invited research into other chemistries. Soluble lead is one such alternative, in which both electrode reactions involve just one active species, Pb²⁺. The electrolyte is inherently safer than many other systems, and proof-of-concept studies have highlighted its suitability for scale-up. In this thesis, the next stage of this process is reported. Fundamental gaps in electrolyte properties, such as conductivity and viscosity, are explored before extensive charge/discharge cycling experiments are carried out in order to optimise the electrolyte, which includes a novel combination of additives. Traditional soluble lead flow cells did not require a separator, which greatly reduced the cost and complexity of the system. However, by inserting a separator and exploring both a standard division and a novel semi-divided configuration, significant improvements to cell efficiency and lifetime are achieved compared to the literature. A flow cell with 100 cm² electrodes is used to investigate the cell power at different states of charge, peaking at 12.5 W. The results also infer that higher currents on discharge can be drawn than from other well-established chemistries. A method of regenerating a failed cell is also shown, where a series of maintenance cycles brings the system close to its initial conditions. The improvements in this project are used to model a flow battery stack, using another commercial device as a benchmark. Unaddressed gaps in the research for the next stage of scaling-up are also discussed.

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

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