Handbook of Energy Storage for Transmission or ... - W2agz.com

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Overall, the reactions that take place at the electrodes are given by the following
equations:
ch arg
⎯⎯⎯
e
Positive Electrode: V 4+ ⎯⎯
→
←⎯
⎯
disch arg e
ch arg
⎯⎯⎯
e
Negative Electrode: V 3+ ⎯⎯
→
←⎯
⎯
disch arg e
V 5+ + e -
V 2+ + e -
Electrolyte is made up of a vanadium and sulfuric acid mixture at approximately the same
acidity level as that found in a lead-acid battery. It is stored in external tanks and pumped
as needed to the cells. Electrolyte concentration changes according to the state of charge.
The cell is divided into two “half-cells” by a proton exchange membrane (PEM). This
membrane separates the two different vanadium-based electrolyte solutions – the anolyte
and the catholyte – and allows for the flow of ionic charge (protons, or H+ ions) to
complete the electrical circuit.
Cells have a nominal voltage of about 1.2 V (DC) as defined by the electrochemical
properties. To achieve useful voltages (such as those used as inputs to a DC-to-AC
power conversion system), cells are combined (“stacked”) electrically in series. In most
constructions, “cell stacks” are fed by distributing electrolyte through a manifold to each
cell. Figure 3 illustrates a typical parallel-feed cell-stack design that combines electrodes,
membranes, and frames.
Vanadium Redox Battery 9