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A Better Battery? The Lithium Ion Cell Gets Supercharged

A new technique could pave the way for improving the workhorse lithium ion battery used in automobiles, cell phones and other devices so that it can recharge in seconds



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A new twist on the familiar lithium ion battery has yielded a type of power-storing material that charges and discharges at lightning speed. The finding could offer a boost for plug-in hybrid and electric vehicles and possibly allow cell phone batteries to regain a full charge in seconds rather than hours.

Scientists at the Massachusetts Institute of Technology (M.I.T.) report in Nature today that they devised a way for lithium ions in a battery to zip in and out about 100 times faster than previously demonstrated. "We took a basically great material called lithium iron phosphate [LiFePO4] and we tried to improve it further," says study author Byoungwoo Kang, a graduate student in M.I.T.'s Department of Materials Science and Engineering.

Rechargeable lithium ion batteries are small and light, yet can store copious amounts of energy, making them ideal for use in everyday electronic devices such as iPods and laptops. This valuable property, called energy density, can be scaled up for hybrid cars as well as for the all-electric Roadster built by Tesla Motors that relies on lithium ion batteries (6,831 individual cells) and the similarly powered Chevy Volt plug-in electric, about to hit the market.

One downside: lithium ion batteries do not dispense their charge—carried by lithium ions and electrons, hence the power source's name—very quickly compared with some other types of storage batteries. Like a huge auditorium that only has a few doors, getting a large volume of patrons (lithium ions) in and out is a drawn-out affair. This phenomenon explains why some electric vehicles (the rip-roaring $109,000 Tesla Roadster with its massive battery pack excluded) can reach high speeds, but they suffer from poor acceleration compared with the propulsive force unleashed by the rapid succession of mini explosions in an internal combustion engine. The slow exchange of ions also means lithium ion batteries recharge slowly—just think of how long you have to charge your tiny cell phone.
 
In an attempt to pick up the pace, the M.I.T. researchers coated the lithium iron phosphate material with an ion conductor, which in this case was a layer of glasslike lithium phosphate. Sure enough, the charge-carrying ions traveled much faster from their storage medium; a prototype battery the scientists built completely charged in about 10 to 20 seconds.

The results have impressed some battery experts. "I think this work is a really exciting breakthrough with clear commercial applications," says Yi Cui, an assistant professor of materials science and engineering at Stanford University.

Two companies have already licensed the technology, according to Kang.  Researchers are not sure how much these batteries will cost when they hit the market, but Kang says they should be reasonably priced, given that it should be relatively cheap to produce them.

The study notes that residences cannot draw enough energy from the electrical grid to quickly charge a hybrid car's battery containing the new material, though smaller batteries for gadgets and perhaps power tools should not have that catch. But future roadside plug-in stations (service stations selling electricity instead of gasoline) with greater power pull could do the trick for vehicles, Kang says.

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