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More Powerful Batteries

A new, fast-charging battery will make drills and hybrid cars more powerful.
November 21, 2005

Lithium ion batteries have been powering cell phones and laptops for years. But they were not used for more power-hungry machines like power tools and hybrid vehicles, mainly because of their high cost, their inability to provide adequate current, and safety issues.*

All this has now changed, though, according to A123 Systems. This month the Watertown, MA startup announced a new lithium ion battery, based on research done at MIT, that’s suitable for applications requiring high power output. The battery’s high power density – a measure of the watts of power it can produce per kilogram – means it’s also lighter than conventional batteries of similar size. The battery will get a chance to prove itself soon: it’s being incorporated into a new line of power tools, scheduled to reach store shelves next spring, that can outperform plug-in drills and saws.

“The first customer is a power tool company, but the cell can be used in many types of applications, such as automotive environments or medical devices – anything that needs high power,” says Ric Fulop, A123’s co-founder and vice president of business development.

Yet-Ming Chiang, whose work as an MIT professor of materials science led him to co-found A123 with Fulop, says “this is a battery system that could have significant impact on hybrid electric vehicles.”

At about the same weight as an 18-volt drill battery, the new battery can deliver 36 volts, according to Baltimore MD toolmaker DeWalt, which is producing a new line of seven products that use the battery. Chiang says A123’s batteries can produce 3,000 watts of peak power, twice as much as a drill or saw designed to be plugged into a wall outlet.

That means that when the blade of a circular saw starts to bind up, the saw can power through it. “Having this high peak power capability allows you to do a great deal more work because you don’t get bogged down,” says Chiang.

The new batteries are based on an advance by Chiang in his lab at MIT’s department of materials science and engineering. He was working with a material, lithium iron phosphate, that promised high capacities for batteries. But it had a significant problem: an inability to handle large currents.

Chiang found that doping the material gave it very high conductivity. His success in the lab led him to found a startup to commercialize the technology. Chiang declines to give details of A123’s current battery, including whether or not it uses iron, but does say it uses an inexpensive lithium metal phosphate in the battery’s cathode, the electrode that receives electrons during discharge.

Eventually, according to Chiang, batteries based on the technology could replace those in hybrid vehicles, at one-fifth of the weight, potentially leading to either better gas mileage or higher battery performance for the same weight. The company has been talking to auto manufacturers, and the U.S. Department of Energy is currently evaluating the batteries to see if they meet the benchmarks for cycle life (the number of times a battery can be recharged) and power for hybrid vehicles. Chiang also suggests that the batteries could be used in power lawn mowers, vacuum cleaners, and electric scooters.

The company says the batteries can withstand ten times more rechargings than other lithium ion batteries, can be charged to 90% capacity in just five minutes, and can be fully charged in less that 15 minutes.

Another advantage of using lithium iron phosphate is its lower cost. Right now, lithium ion batteries use cobalt instead of iron in the cathode. Cobalt is far more expensive than iron.

“What the world needs is not another battery,” says MIT electrochemist Donald Sadoway. “What the world needs is a high-performance, cheap battery. If people can build a high-performance battery that relies on iron, that’s a big step forward.”

The new batteries also address a major concern with powerful lithium ion batteries: safety. According to Chiang his new material is “chemically so stable” that it results in a battery that is much less likely to leak or explode.

* The original version of the story read: “But they’ve never been used for more power-hungry machines like power tools and hybrid vehicles, mainly because of their high cost, their inability to provide adequate current, and safety questions.” The phrase “never been used” was changed because E-One Moli Energy Ltd., Maple Ridge, B.C., Canada, has produced a version of a lithium ion battery that was introduced for use in power tools at the beginning of this year.

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