Vanadium Redox Flow Battery-SECONDARY BATTERIES – FLOW SYSTEMS | Overview


Vanadium Redox Flow Battery

SECONDARY BATTERIES – FLOW SYSTEMS Overview

from M.J. Watt-Smith, … F.C. Walsh, in Encyclopedia of Electrochemical Power Sources

The vanadium–vanadium redox flow battery (VRB) was largely pioneered by M. Skyllas-Kazacos and coworkers in 1983 at the University of New South Wales, Australia. The technology is now being developed by several organizations including E-Fuel Technology Ltd in the United Kingdom and VRB Power Systems Inc. in Canada. A particular feature of the VRB is that it employs the same chemical element in both the anode and the cathode electrolytes. The VRB utilizes the four oxidation states of vanadium, and ideally there is one redox couple of vanadium in each half-cell. The V(II)–(III) and V(IV)–(V) couples are used in the negative and positive half-cells, respectively. Typically, the supporting electrolyte is sulfuric acid (∼2–4 mol dm−3) and the vanadium concentration is in the range of 1–2 mol dm−3.

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The charge–discharge reactions in the VRB are shown in reactions [I]–[III]. During operation, the open-circuit voltage is typically 1.4 V at 50% state-of-charge and 1.6 V at 100% state-of-charge. The electrodes used in VRBs are usually carbon felts or other porous, three-dimensional forms of carbon. Batteries of lower power have employed carbon–polymer composite electrodes.

A major advantage of the VRB is that the use of the same element in both half-cells helps to avoid problems associated with cross-contamination of the two half-cell electrolytes during long-term usage. The electrolyte has a long lifetime and waste disposal issues are minimized. The VRB also offers high energy efficiency (<90% in large installations), low cost for large storage capabilities, upgradability of existing systems, and long cycle life. Possible limitations include the relatively high capital cost of vanadium-based electrolytes together with the cost and limited lifetime of the ion-exchange membrane.