As our society becomes increasingly mobile, while at the same time getting more and more connected, batteries are becoming more widespread and more important. Two years ago, Americans purchased close to three billion batteries a year. With the explosive growth of iPod and cell phones markets, the demand is far higher now. It’s a good thing that many of those devices use rechargeable batteries, otherwise we’d probably be buying ten billion batteries a year, many of which would end up in landfills.
Most of the rechargeables in use today are lithium ion, which took over from nickel metal hydride, which took over from nickel cadmium. This has allowed us to carry smaller and smaller devices that can still run a full day or longer between charges. So what would an even better battery allow us to do?
That’s a question that the folks at ReVolt Technology are very interested in. They have been working on zinc-air batteries which can potentially hold lots more energy for their size than any other battery. You might wonder if cell phones got any smaller, if you’d even be able to hold them, or dial them, or, heaven forbid, text on them. But then you might be missing the point.
The ultimate planetary payoff for battery technology is not smaller cell phones but to replace fossil fuel applications, like cars, for instance, with electric bicycles, or eventually electric cars. Because electricity, unlike fossil fuel,or even bio-fuel, can be produced and consumed using renewable, carbon-free methods; this appears to be the cleanest possible road.
Zinc-air batteries have been around for a long time. They are commonly used for hearing aids and watches, as well as for remote applications for telecoms or railway signaling and for electric fencing. They have long been considered one of the most promising battery types due to their very high energy density, which could enable them to store up to ten times the energy of a comparably sized lithium ion. This could have huge potential for automobile applications. IBM has been actively involved in researching these batteries at their Almaden Research Center in San Jose. The current state-of-the-art lithium battery can allow the Chevy Volt to travel 40 miles before requiring a charge. According to IBM’s Chandrasekhar Narayan, “To really make an impact on transportation and on the grid, you need higher energy density than that.” Revolt’s goal is to produce a battery that will allow an electric family sedan to travel 500 miles without a charge.
The reason zinc-air batteries have not had a bigger presence in the market in the past, is because it has been difficult to make them rechargeable. Because this battery has to be open to the atmosphere in order to react with the air, it can dry out, which will deplete its charge. It can also become contaminated by humidity, or the zinc electrode could form branch-like structures called dendrites that could eventually form an electrical short circuit. But ReVolt, working with technology originally developed at the SINTEF research institute in Norway, has developed a battery that controls the shape of the zinc electrode and the humidity within the cell.
ReVolt’s electric vehicle battery resembles a fuel cell. One electrode will be a liquid- zinc slurry. The air electrodes will be comprised of tubes. The zinc slurry, will be pumped through the tubes where it will oxidize, releasing electrons in the process. The resulting zinc oxide accumulates in a separate compartment. As the battery is recharged, the zinc oxide flows back through the air electrode, releasing the oxygen, and forming zinc once again.
ReVolt’s CEO James McDougall claims these batteries could last for as many as 2,000 to 10,000 cycles. Additionally, the battery is designed so that the electrodes can be replaced separately when they wear out, reducing cost and waste. Another advantage of using zinc over lithium is that zinc is more plentiful and accessible.
The company recently received a $5 million award from DOE’s ARPA-E program. These funds will allow it to accelerate its implementation plan for a U.S. headquarters and development facility in Portland, Oregon, where it will work on advanced zinc-air battery technology for use in electric vehicles.
RP Siegel is the co-author of the novel Vapor Trails, the first volume of a sustainability trilogy about energy, food, and water.
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