This series of papers will describe the chemistry, electrochemistry and performance of a flow battery with no separator and a single electrolyte, lead(II) in methanesulfonic acid. Voltammetry at rotating disc electrodes is used to define the conditions for the high rate deposition and dissolution of lead and lead dioxide in aqueous methanesulfonic acid. The determination of lead methanesulfonate solubility and solution conductivity as a function of lead methanesulfonate and methanesulfonic acid concentrations was carried out in order to aid the selection of the electrolyte for the battery.

The design and performance of a small redox flow battery is described; it is based on a single undivided, parallel plate cell with carbon electrodes and an acidic lead methanesulfonate electrolyte. It is shown that the cell operates as a secondary battery at charge/discharge current densities of 10–60 mA cm⁻². Typically, the voltage during discharge is ∼1.55 V, Coulombic efficiency >85% and the energy efficiency ∼65%.

In this paper, a mathematical model for the all-vanadium battery is presented and analytical solutions are derived. The model is based on the principles of mass and charge conservation, incorporating the major resistances, the electrochemical reactions and recirculation of the electrolyte through external reservoirs. Comparisons between the model results and experimental data show good agreement over practical ranges of the vanadium concentrations and the flow rate. The model is designed to provide accurate, rapid solutions at the unit-cell scale, which can be used for control and monitoring purposes. Crucially, the model relates the process time and process conditions to the state of charge via vanadium concentrations.