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Saturday, May 8, 2010

Will Lithium-Air Battery Rescue Electric Car Drivers From 'Range Anxiety'?

Twenty miles southwest of Chicago, government researchers are pursuing the automotive version of Mr. Right. He's powerful. He has endurance. He isn't too expensive to have around. And he never, ever explodes.

That's one way to think of the perfect car battery, which will have to balance many different factors to lure the American masses to the electric car. For the moment, though, Mr. Right is just a set of equations in a notebook.

"Theoretically, it works on paper," said Don Hillebrand, who directs the Center for Transportation Research at Argonne National Laboratory.

At Argonne National Laboratory and elsewhere, researchers are just beginning to crack the basic science behind a promising technology: lithium-air batteries. If their theories are right, these batteries will have five to 10 times the energy of lithium-ion batteries, the big battery pack that's powering the first wave of electric-drive cars.

"Lithium-air is where we're going," Hillebrand said. "You can't foresee the future, but right now, that's the place where I think we see the endpoint, the end solution for ... the battery. The battery everybody's looking for."

But as engineers get closer to perfecting the lithium-ion variety, lithium-air has a long journey to replace the batteries of yesteryear.

A good idea that's still en route

"Nickel-metal hydride's an adult. Lithium-ion is a developing adolescent. And lithium-air, we're just looking at the ultrasounds," Hillebrand said.

Some say lithium-air will only carry triple the energy of lithium-ion; others project a hundredfold increase. Regardless of the estimates, all agree that lithium-ion could use a tuneup.

The reason has to do with "battery chemistry," a term that describes what makes the device go.

Batteries have an anode and a cathode, two materials that exchange ions -- in this case, lithium ions. When the ions go one way, the battery charges up; when they go the other way, the battery releases its charge.

Different materials for the anode and cathode, of course, affect this back-and-forth movement. For example, they can speed it up, move a larger number of ions, or reduce the number of times the battery can repeat the exchange -- that is, shorten the battery's life.

Lithium-ion chemistry is considered an improvement over past efforts to power electric cars. Previous options were so large and heavy that they were just barely economical to lug around. Lithium-ion packed so much more energy into less space and weight that major automakers christened it for their latest lineup of electric and hybrid cars, including Toyota's Prius, General Motors' Volt, and Nissan's Leaf.

The change came at a price, though. Today, lithium-ion batteries are commonplace and commercialized for laptops and cell phones. But the larger batteries needed for cars remain their most expensive component -- and the one deemed most essential to helping millions reach the road.

In the coming years, many expect these costs to decline. Even so, plenty in the battery field foresee the day that lithium-ion, so essential to the present day, will face retirement.

A battery that could challenge petroleum

"Let's say we want to electrify the entire fleet of vehicles in the world," said Jeffrey Chamberlain, head of Argonne's Energy Storage Major Initiative and one of the lab's leading battery chemists. "Lithium-ion batteries will get us partway there. But in reality, they're not quite high enough in energy density or quite low enough in cost."

He called lithium-air a "dream-type battery": Look at the periodic table, he said, and the only element that carries more energy than lithium, for its weight, is hydrogen. If the models are right, lithium-air could get to that energy far better than lithium-ion, approaching the limit of what a battery can do. It could even rival the energy density of petroleum -- one of the most energy-packed substances on earth.

That would tectonically shift the economics of electric cars. Right now, carmakers face "range anxiety": They worry Americans will hesitate to buy an electric car that can only go a few dozen miles.

Chamberlain said lithium-air could banish that fear. "You really imagine instead of going 40 miles between charges, you could go 200 or 400 miles," he said.

The key to lithium-air is weight loss. Yang Shao-Horn, an associate professor of chemistry at the Massachusetts Institute of Technology, said lithium-ion batteries stuff lithium into a compound with metal and oxygen to keep it stable and play pingpong with the lithium ions.

Trading heavy metal for a battery that 'breathes'

A lithium-air battery, by contrast, skips the metal and attaches lithium to oxygen alone. On the other side of the battery, there's a porous material that "breathes" in oxygen and can play the other side of the pingpong table. Without the extra metal, Shao-Horn said, the battery gets much lighter, but without compromising the ability to hold energy.

But before the technology goes commercial, researchers have to pass a gantlet of scientific challenges. A material may "breathe" oxygen into the battery excellently, but it has little commercial potential if it's platinum or gold. Lithium in the anode reacts explosively with even a little water, so it must be sheltered with a stable and, yes, cheap substance.

Argonne guesses lithium-air could be 10 to 20 years from commercial readiness; Shao-Horn of MIT has said 10 years is probably too optimistic.

Part of the reason is that scientific work takes a long time to percolate to auto showrooms. Ronn Jamieson, General Motors' director of global battery systems, explained how every new battery idea has to undergo a vetting process that doesn't exactly zoom.

At any given moment, he said, GM knows of over a hundred ideas for battery chemistries being proposed by universities, laboratories and other companies.

He said GM doesn't dismiss any of these out of hand, but the first step is to check the science textbooks: "Is it physically possible? Does it defy the laws of physics or thermodynamics or anything else?"

If it passes that test, GM does what Argonne and everyone else do: They find one and beat it up.

Some researchers stick a battery cell in an oven for a year, gradually turning up the heat to 113 degrees and then 131 degrees Fahrenheit. Others dunk it in a swimming pool. Others short the battery and see if it blows up. One Department of Energy researcher shot a battery with a nail gun.

These aren't likely situations for electric cars, but battery developers want to be sure. They say just one high-profile mishap could spell doom for the technology. And so, Jamieson said, GM subjects every new battery technology to a year or more of tests.

In the labs, the U.S. may be leading the race

"Theoretically, if it can happen, you've got to at least assess and understand what will happen," he said.

If lithium-air is the "silver bullet" of the future, there are a host of lead bullets poised to come sooner. GM said it's working on lithium-air, next-generation lithium-ion, and other chemistries. Nissan and Toyota representatives didn't specifically mention lithium-air, but they said their advanced battery labs -- partnering with Japanese companies NEC and Panasonic -- are examining various chemistries.

The White House is looking to nudge the process, as indicated by DOE grants last week. The Advanced Research Projects Agency-Energy program awarded $34 million last week for breakthrough research in auto batteries. Two grants went to lithium-air proposals, but other ideas varied, from magnesium-ion to zinc-air to an "all electron" battery from Stanford University and Honda.

If they and other researchers make progress on the technology, the United States may be poised to grab the global lead. In an e-mail, Hillebrand said lithium-air is too young for any country to have cornered the technology, but "the U.S. and Japan have both recognized the potential, and the U.S. is probably ahead."

In an interview, he said Tokyo is funding labs that focus on lithium-air, among other chemistries. He hadn't heard of the technology developing in China or Korea: "I'd be surprised if it wasn't, though."

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1 comment:

chicago auto car dealerships said...

I certainly respect Nissan and any of the other companies that have to make a decision — hopefully a short-term decision,” said Carl Galeana, cochair of the Detroit show. “It’s tough for everyone right now.

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