Lasted edited by Andrew Munsey, updated on June 14, 2016 at 9:23 pm.
: For a list of resources, see Directory:Vanadium Redox Batteries
The vanadium redox battery (or redox flow battery) exploits the ability of vanadium to exist in 4 different oxidation states, and uses this to make a battery that has just one chemical electrolyte instead of two.
The battery was first patented by the University of New South Wales in Australia in 1986. It is a type of rechargeable battery that was originally suggested by NASA researchers and by Albero Pellegri and Placido Spaziante, in 1978, but the first successful demonstration and commercial development was by Maria Skyllas-Kazacos and co-workers at the University of New South Wales in 1984.
The main advantages of the vanadium redox battery is that it can offer almost unlimited capacity simply by using larger and larger storage tanks, it can be left completely discharged for long periods with no ill effects, it can be recharged simply by replacing the electrolyte if no power source is available to charge it, and if the electrolytes are accidentally mixed the battery suffers no permanent damage. The main disadvantages with Vanadium redox technology are a relatively poor energy-to-volume ratio, and the difficulty in storing and handling large volumes of the (somewhat corrosive) liquid electrolytes.
A Vanadium redox battery consists of a power cell in which two electrolytes are kept separated by an ion exchange membrane, somewhat confusingly, both electrolytes are vanadium based. The electrolyte in the positive half-cell contains VO2+ and VO2+ ions, the electrolyte in the negative half-cell, V3+ and V2+ ions. This electrolyte is typically prepared by electrolytically dissolving vanadium pentoxide (V2O5) in sulphuric acid (H2SO4) and the solution remains strongly acidic in use.
It should be noted that National Power in the UK have also developed a redox flow battery, but one that is based on the use of two very different solutions, one of sodium sulphide and one of sodium bromide. While this system appears to give a higher power density it does carry additional problems as cross-contamination of the electrolytes is destructive to the battery.
In vanadium flow batteries, both half-cells are additionally connected to storage tanks and pumps so that very large volumes of the electrolytes can be circulated through the cell. This circulation of liquid electrolytes is somewhat cumbersome and does restrict the use of vanadium flow batteries in mobile applications, effectively confining them to large fixed installations, although there is one company focusing on electric vehicle applications, where rapid replacement of electrolyte is used to refuel the battery.
When the vanadium battery is charged, the VO2+ ions in the positive half-cell are converted to VO2+ ions when electrons are removed from the positive terminal of the battery. Similarly in the negative half-cell, electrons are introduced converting the V3+ ions into V2+. During discharge this process is reversed and results in a typical open-circuit voltage of 1.40 V at 25 °C.
Other useful properties of Vanadium flow batteries are their very fast response to changing loads and their extremely large overload capacities. Studies by the University of New South Wales have shown that they can achieve a response time of under half a millisecond for a 100% load change, and allowed overloads of as much as 400% for 10 seconds.
The extremely large capacities possible from vanadium redox batteries make them well suited to use in large power storage applications such as helping to average out the production of highly variable generation sources such as wind or solar power, or to help generators cope with large surges in demand. Their extremely rapid response times also make them superbly well suited to UPS type applications, where they can be used to replace Lead-acid batteries and even diesel generators.
Currently installed vanadium batteries include:
A 1.5MW UPS system in a semiconductor fabrication plant in Japan
A 275 kW output balancer in use on a wind power project in the Tomari Wind Hills of Hokkaido
A 200 kW, 800kWh output leveler in use at the Huxley Hill Wind Farm on King Island, Tasmania
A 250 kW, 2MWh load leveler in use at Castle Valley, Utah
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Vanadium Redox-Flow Battery (VRB) for a Variety of Applications. Presentation paper from the IEEE summer 2001 conference, SUMITOMO ELECTRIC INDUSTRIES, Ltd.
The Vanadium Redox Battery. The University of New South Wales.
vanadium redox batteries and fuel cell for large scale energy storage. 19th World Energy Congress, September 2004. (Sydney, Australia)
Wikipedia contributors. Vanadium redox battery. Wikipedia, The Free Encyclopedia. July 6, 2006.