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The University of Southampton

Research project: The Soluble Lead Redox Flow Battery (SLFB)

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Redox flow batteries offer many advantages over competing large-scale energy storage technologies: they are mobile, scalable from a few kWs to many MWs, and unlike other battery types, can be customised to suit power specific or energy specific applications, since the energy storage media is dissolved in liquid electrolyte and stored in external reservoirs. A flow battery consists of a stack of single cells through which the electrolyte is circulated using pumps.


The SLFB is one type of redox flow cell which makes use of the variable oxidation states of lead, Pb2+ and Pb4+. In its simplest form, Pb2+ ions are dissolved in an aqueous methanesulfonic acid medium and this electrolyte is then pumped through an undivided electrochemical cell. During charge at the positive electrode, Pb2+ ions are oxidised, leading to a deposit of solid lead dioxide on the electrode. Each ion is stripped of two electrons that flow through an external circuit to the negative electrode. Here, each Pb2+ ion gains two electrons and following reduction, there is a corresponding phase change where solid lead is deposited onto the electrode. The thicknesses of the deposits relate to the energy stored. During discharge, the electrodeposits dissolve back into the solution, releasing the stored energy (Figure 1). Unlike other flow cell chemistries, the SLFB uses an electrolyte common to both electrodes and a membrane is therefore not required. There is only one tank and one set of pipework, which greatly simplifies the design of the system and makes this potentially much cheaper than other flow battery chemistries.

The SLFB flow cell has a typical discharge voltage of 1.5 V. The cell has been shown to operate for 300+ hours with an energy efficiency of 75 % and a storage capacity of 24 Wh Kg-1. All of the electrolyte components are non-volatile liquids that can be contained within a bund should any leaks occur. Furthermore, the supply of materials can be integrated with current lead recycling activities. The system is still at an early stage of development and these results indicate that the system is suitable to be scaled-up. The system is well aligned with industrial and commercial needs, such as having a low maintenance, simple cell design with low internal voltage losses. The intention of the proposed project is to advance the SLFB from lab scale to a 5 kW stack, ensuring the technique and the materials involved are scalable. While the focus of the project is the enablement of the technology for intelligent grid management, it clearly has broad applicability to any industrial sector with an energy storage requirement.

Figure 1 The Soluble Lead Flow Battery. A simplified cell-reservoir loop for the undivided SLFB. A pump is used to circulate electrolyte around the system. During charge, Pb2+ ions are oxidised at the positive electrode to form solid PbO2 and reduced at the negative electrode to form solid Pb. The process is reversed during discharge (figure not to scale).

Project Partners:

The Department of Energy & Climate Change

C-Tech Innovation Ltd

University of Warwick


The Soluble Lead Flow Battery
Figure 1

Related research groups

Energy Technology

Key Publications

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