'Air' Batteries Could Energize EVs

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Scientists are pushing to improve charging capabilities of lithium air batteries because they use cheap and lightweight oxygen to generate energy.
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THE GIST

- A critical technique has been developed that allows lithium-air batteries to be recharged many times.

- Lithium-air batteries promise three to five times as much energy as lithium-ion.

- Such a battery would allow a person to talk for a week without charging a cellphone or drive 500 miles in a Chevy Volt.

A benign gas could be the most powerful thing yet tapped to energize your electronic devices: Air. Researchers in the UK say they 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 batteries that we use in our consumer devices and electric vehicles.

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 cellphone or even a take a 500-mile journey in a Chevy Volt, for example, instead of the 100 miles it runs today.

The experiment by Peter G. Bruce, professor of chemistry 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.

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"We have demonstrated that sustainable cycling is possible," said 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, Bruce said, 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 Berkeley, Calif., based firm that is building advanced lithium-sulfur, lithium-seawater and lithium-air batteries.

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Bruce "is the first to get reversible cycling, which is exciting," Visco said. "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 said 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," Bruce said. "What we've done demonstrates the importance of basic scientific studies in this area. If you rush out and try to make a battery in with knowledge that currently existed you would be unlikely to succeed."