News in Science

'Air' batteries could energize EVs

Electric jumpstart UK researchers have made a key step in development of a lithium-air battery, a device that promises three to five times as much energy per unit mass as the existing lithium-ion.

Once built, such a battery could allow you to fly cross-country flights with a functioning laptop, or talk for a week without charging your mobile phone or even a take a 800-kilometre journey in an electric car.

The experiment by Professor Peter G Bruce at the University of St. Andrew's in Scotland, and colleagues was published today in online journal Science Express. It describes a chemical reaction that allows the battery to be recharged without degradation of the battery's electrode.

"We have demonstrated that sustainable cycling is possible," says Bruce. "That is the real step here. We haven't solved all the practical problems and it's not a solution, but it does demonstrate this critical reaction can be sustained and cycled."

Scientists are pushing to develop a lithium air battery because they use air as the cathode and lithium metal as the anode. Oxygen is both cheap and light. It doesn't require the battery to be built with heavy casing to contain the electrodes.

In existing batteries, lithium ions move from the cathode to the anode through an electrolyte, or a chemical solution. When you use the battery, the process is reversed and the flow of ions produce an electric current.

In a lithium-air battery, oxygen enters the cathode and combines with lithium ions to produce lithium peroxide, which accumulates as the battery is discharged.

The Scottish team was able to produce this chemical reaction over and over again without decomposition, says Bruce, using a thin film of porous gold as an electrode.

That may be the battery's Achilles heel, says Steve Visco, president and CEO of Polyplus, a California-based firm that is building advanced lithium-sulfur, lithium-seawater and lithium-air batteries.

Bruce "is the first to get reversible cycling, which is exciting," says Visco. "Hopefully it's not only gold that does it, which would not be practical unless you are sending it into space where cost doesn't matter. It certainly wouldn't work for electric vehicles."

Bruce says that his experiment is one of many that have to be successful before this Holy Grail of advanced battery technology is built.

"It's still a long way off," says Bruce. "What we've done demonstrates the importance of basic scientific studies in this area. If you rush out and try to make a battery with the knowledge that currently existed you would be unlikely to succeed."