For large-scale energy storage, the rules are very different. Typical rechargeable batteries are unsuitable because it is difficult to get a lot of energy out of them quickly; when the grid is on the verge of crashing, you want an energy infusion now. Ordinary rechargeables also wear out easily. A typical laptop battery will die after a few hundred charge-discharge cycles. In contrast, flow batteries can be charged and discharged many thousands of times.
A vanadium battery generates electricity in a stack,
where electrolytes with different
oxidation states (indicated by the numbers)
are allowed to react via a central membrane,
so that V(+5) becomes V(+4)
and V(+2) becomes V(+3). Bigger tanks
allow more electricity to be stored.
VRB Power Systems
The vanadium battery’s indefatigable nature echoes that of its creator, Skyllas-Kazacos, a single-minded researcher whose no-nonsense manner is frequently punctuated by an unexpected easy laugh. Her path to the vanadium battery began quite by accident in 1978 at Bell Laboratories in Murray Hill, New Jersey, where she was a member of the technical staff. She had applied to work on solar energy. At the time, Bell Labs was developing liquid-junction photovoltaics (a type of solar cell that employs liquid electrolytes), which seemed like a nice fit for her electrochemical training. But the director of the lab’s battery section picked up her job application first and liked what he saw. Much to her surprise, when Skyllas-Kazacos arrived she was assigned to do research on batteries, which she had never worked on before.
Her serendipitous experience in batteries was put to good use five years later after her return to Sydney, where she had grown up after immigrating with her family from Greece in 1954. She took a position at the University of New South Wales. A colleague there asked her to co-supervise a student who wanted to investigate ways of storing solar energy. The project sounded interesting, so she agreed.
Skyllas-Kazacos started her research by building on the foundational work on flow batteries done by NASA in the mid-1970s. The space agency’s scientists recognized that flow batteries could store solar power on a spacecraft, but they gave up on them after hitting a snag known as cross-contamination. When two liquid electrolytes made of different substances are separated by a membrane, sooner or later the membrane is permeated and the two substances mix, rendering the battery useless. The early NASA flow batteries, which used iron and chromium, quickly ran down as a result.
“We thought the way to solve this problem was to find an element that could be used on both sides,” Skyllas-Kazacos says. Technically, cross-contamination would still occur, but with essentially the same substance doing double duty, the problem would be moot. The key was to pick an element that could exist in a variety of electrical, or oxidation, states.
Skyllas-Kazacos chose vanadium, a soft, bright white, relatively abundant metal named for Vanadis, the Scandinavian goddess of beauty and youth. Vanadium has four oxidation states, known as V(+2), V(+3), V(+4), and V(+5); in each state the element carries a different amount of electric charge. Often oxidation states are hard to tell apart, but in this case nature was kind: V(+2) is purple, V(+3) green, V(+4) blue, and V(+5) yellow.
Simply having different oxidation states is not enough to make an element work for a liquid battery. The element has to be soluble, too. NASA had considered and rejected vanadium because the technical literature insisted that the solubility—and hence energy density—of the useful V(+5) form of the element was extremely low. Skyllas-Kazacos recognized, however, that just because something appears in print does not necessarily mean it is true. Previous studies had started by leaving a compound of vanadium, vanadium pentoxide, to dissolve in solution. This was a very slow process that could take days, and it never produced more than a tiny amount of V(+5) in solution. Skyllas-Kazacos approached the problem from a less direct route. “I started off with a highly soluble form, V(+4), then oxidized it up to produce a supersaturated solution of V(+5). I found that I could get much higher concentrations. From then on it became clear that the battery would actually work.”
In 1986 came a major milestone: Her university filed for a patent on the Skyllas-Kazacos vanadium battery. But proving the concept turned out to be the easy part. “We thought we would take the device to a certain level, and then some industry group would come and take it off our hands,” Skyllas-Kazacos says with her laugh. “What we didn’t realize was that the task was enormous. We had to develop the membranes, the conducting plastic for the electrodes, the structures, the materials, the designs, the control systems—everything!” In 1987 Agnew Clough, an Australian vanadium mining company, took out a license on the technology. But nothing came of the deal.
The vanadium battery finally got its first chance to shine in 1991, when Kashima-Kita Electric Power, a Mitsubishi subsidiary located north of Tokyo, took out a new license on the technology. Kashima-Kita powers its generators with Venezuelan pitch, a fuel rich in vanadium. Skyllas-Kazacos’s battery was a perfect fit. Here was a technology that allowed the company to recycle the vanadium from its soot and flatten out fluctuations in demand for its electricity at the same time. The world’s first large-scale vanadium battery went into operation in 1995, able to deliver 200 kilowatts for four hours—enough to power about 100 homes. It was a success, but Kashima-Kita sold the license and didn’t build another.
The buyer, Sumitomo Electric Industries, a giant Osaka-based company, had been working on NASA-style iron-chromium flow batteries since the early 1980s. Things looked up for Skyllas-Kazacos’s invention when Sumitomo switched to vanadium and licensed the technology in 1997. Three years later Sumitomo began selling vanadium batteries, including a 1.5-megawatt model that provides backup power to a Japanese liquid crystal display factory. By maintaining power during blackouts and thus preventing production losses, the battery reportedly paid for itself in six months.
Sumitomo sold a 1.5-megawatt battery that provides backup to a liquid crystal display factory. ?by maintaining power in blackouts and preventing?production losses, it paid for itself in six months.
Sumitomo has since demonstrated vanadium technology in at least 15 other implementations, including a 170-kilowatt battery at a wind farm in Hokkaido. All are located in Japan, their development subsidized by the government. Sumitomo doesn’t sell outside Japan, possibly due to the battery’s high manufacturing cost.
One company is now taking up the vanadium banner worldwide: VRB Power Systems, a Vancouver, British Columbia, start-up that bought most of the early intellectual property rights to the technology. The company is targeting the market for hybrid systems used to power remote, off-grid telecom applications. “In places like Africa, cell phone towers are typically powered by little putt-putt diesel engines that run 24/7,” VRB CEO Tim Hennessy says. By adding a vanadium battery to the system, one can run the diesel generator while charging the battery, turn the diesel off, run the battery, then repeat the cycle nonstop. “The beauty of the battery is that you can cycle it as many times as you like,” Hennessy says. “The electrolyte doesn’t wear out.”
VRB has installed 5-kilowatt batteries at two sites in Kenya. Hennessy claims that these can produce “at least a 50 percent reduction in the burning of diesel fuel, plus the diesels will need less maintenance and last much longer. It promises to make a huge difference to our customers’ operating expenses.” The firm’s other recent sales include a 20-kilowatt system, worth $300,000, that will deliver nine hours of backup power for an undisclosed major telecom company in Sacramento, California. These customers are learning firsthand what Skyllas-Kazacos learned two decades ago. The vanadium battery really works.
