Science
5:09 pm
Fri January 18, 2013

Powerful But Fragile: The Challenge Of Lithium Batteries

Originally published on Fri January 18, 2013 7:58 pm

Boeing announced late Friday that it is postponing deliveries of its new 787 Dreamliner because of problems with its big batteries. Aviation authorities in the U.S. and abroad grounded the new jetliners after those batteries failed in two planes operated by Japanese airlines, including one battery that burned while the plane was on the ground.

These lithium-ion batteries are new to jetliners. They're powerful and lightweight, and, unfortunately, they're also fragile.

"Everyone's carrying a lithium-ion battery in their pocket today," says chemical engineer Vince Battaglia at Lawrence Berkeley Lab in Berkeley, Calif. They're in cellphones, laptops, cameras — small electrical devices thrive on them. "And there's not a big issue" about them going up in flames now and then.

Lithium-ion batteries produce twice the voltage traditional batteries do. And when they go bad, that power turns into heat. The reason it's not such a big deal, Battaglia says, is that the batteries are usually smaller than a pinkie. "The energy is small. It's easy to get the heat out of that little battery"

A small battery loses its heat quickly. But if you supersize that battery, up to, say, the size of a big suitcase, it's harder to get rid of the heat.

"When you go to these bigger cells, you've got all the heat in one cell," Battaglia says. "You've got to get it out."

You do that by using fans or circulating a coolant around the battery. That works fine so long as the battery is intact. But chemical engineers know that lithium-ion batteries have an Achilles' heel for two reasons.

One is the fluid inside the battery, called the electrolyte. Positive and negative ions flow back and forth through the electrolyte, which creates electricity. In normal batteries the electrolyte is an acidic water. In lithium-ion batteries, it's a flammable organic compound.

Donald Sadoway, an engineer with MIT, notes that "if you do get up to temperature, you've got fuel there. It'll burn."

And you can get high temperature because of the second weakness. It's a thin membrane inside the battery that it regulates the flow of ions in that electrolyte fluid. If that membrane breaks, the flow of ions gets out of control and the fluid heats up.

"You breach that membrane," says Sadoway, "and now you've got two compounds that want to react with each other violently, and there's nothing to prevent them from doing so."

If it gets hot enough, the electrolyte fluid vaporizes and escapes. Think of that brandy you pour into a hot skillet and light up for a little flambe.

Laptop batteries sometimes burn like this. And one of Chevrolet's Volt electric cars did. After a controlled crash test, the battery's electrolyte got loose and burned the car to a crisp.

Berkeley's Battaglia says these batteries are pretty delicate. He says he'd drive a car with lithium-ion battery, but he worries about what happens when that internal membrane gets damaged. "If I got into an accident, I wouldn't take it into my garage and plug it in," he says.

But Sadoway at MIT says these batteries certainly can be used safely. "We know what the possible failure modes are, and they are defendable," he says. "You can make these lithium-ion batteries absolutely bulletproof, safe and everything else, but the question is, what's your price point?" Who's willing to pay the cost, compared to other batteries?

That price point may be too high for the auto industry. John Hanson, Toyota's environmental and safety manager, says the company uses them in its all-electric vehicles. The company trusts them. But Toyota is looking for alternatives.

"The only thing we have against lithium is that in order to go to the next step in developing vehicles that the mass market will buy," he says, "they have to be less expensive and they have to deliver more range, and we can't get that from lithium."

Their future in airplanes, however, likely hangs on what engineers learn from the two incidents on the Dreamliner.

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Transcript

ROBERT SIEGEL, HOST:

Boeing announced late today that it's postponing deliveries of its new 787 Dreamliner because of problems with the aircraft's big batteries. Aviation authorities in the U.S. and abroad grounded the new plane this week after those batteries failed, possibly overheating, on two planes operated by Japanese airlines. One battery burned while the plane was on the ground. These lithium-ion batteries are new to jetliners.

As NPR's Christopher Joyce reports, they are powerful, lightweight and fragile.

CHRISTOPHER JOYCE, BYLINE: Lithium-ion batteries are all around us.

VINCE BATTAGLIA: Everyone's carrying a lithium ion battery in their pocket today and there's not a big issue.

JOYCE: Vince Battaglia is a chemical engineer at Lawrence Berkeley Lab in California. The batteries are in cell phones, laptops, cameras. They produce twice the voltage traditional batteries do. And when they go bad, that power turns into heat. Battaglia says this is not a big issue because the batteries usually are smaller than your pinkie.

BATTAGLIA: The energy is small. It's easy to get the heat out of that little battery.

JOYCE: A small battery loses its heat quickly. But if you supersize that battery, up to, say, the size of a big suitcase...

BATTAGLIA: When you go to these bigger cells, you've got all the heat in one cell. You've got to get it out.

JOYCE: You do that with fans or circulating a coolant around the battery. That works fine so long as the battery is intact. But chemical engineers know that lithium-ion batteries have an Achilles' heel. Well, more like an Achilles' ankle than heel, two weak spots. One is the fluid inside the battery called the electrolyte. Positive and negative ions flow back and forth through the electrolyte, creating electricity. In normal batteries, the electrolyte is an acidic water. In lithium-ion batteries, it's a flammable organic compound. Donald Sadoway is an engineer with MIT.

DONALD SADOWAY: And so if you do get up to temperature, you've got fuel there. It'll burn.

JOYCE: And you can get high temperature because of the second weakness. It's a thin membrane inside the battery. It regulates the flow of ions in that electrolyte fluid. But if that membrane breaks, the fluid heats up.

SADOWAY: You breach that membrane and now you've got two compounds that want to react with each other violently, and there's nothing to prevent them from doing so.

JOYCE: If it gets hot enough, the electrolyte fluid vaporizes and escapes. Think of that brandy you pour into a hot skillet and light up for a little flambe. Laptop batteries sometimes burn like this. And one of Chevrolet's Volt electric cars did. After a controlled crash test, the battery's electrolyte got loose and burned the car to a crisp. Berkeley's Vince Battaglia says these batteries are pretty delicate. He says he'd drive a car with a lithium-ion battery, but he worries about what happens when the internal membrane gets damaged.

BATTAGLIA: If I got in an accident, I wouldn't take it into my garage and plug it in.

JOYCE: But Sadoway at MIT says these batteries certainly can be used safely.

SADOWAY: You know, we know what the possible failure modes are, and they are defendable. You can make these lithium-ion batteries absolutely bulletproof, safe and everything else. But, you know, the question is what's your price point?

JOYCE: That price point may be too high for the auto industry. John Hanson, Toyota's environment and safety manager, says the company uses them in its all-electric vehicles and trusts them. But Toyota is looking for alternatives.

JOHN HANSON: The only thing that we have against lithium is that in order to go to the next step in developing vehicles that the mass market will buy, they have to be less expensive and they have to deliver more range. And we can't get that from lithium.

JOYCE: Their future in airplanes, however, likely hangs on what engineers learn from the two incidents on the Dreamliner. Christopher Joyce, NPR News.

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