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March 16, 2009
Volume 87, Number 11
p. 6

Materials science

Faster-Charging Batteries

Method creates lithium-ion battery that charges and discharges in seconds

Elizabeth K. Wilson

Lithium ions (blue) can easily diffuse across a specially prepared coating on the surface of LiFePO<sub>4</sub> (Fe is brown; P is lilac; O is red). Courtesy of Tim Mueller
Room to diffuse Lithium ions (blue) can easily diffuse across a specially prepared coating on the surface of LiFePO4 (Fe is brown; P is lilac; O is red).

BY MERELY TWEAKING a synthetic strategy for making a popular lithium-ion battery material, scientists have produced a battery that charges and discharges in a matter of seconds, rather than the minutes needed for typical lithium-ion batteries.

Used in cell phones, laptops, and other devices, Li-ion batteries are attractive because they can hold a lot of charge, yet they're relatively slow to put it out or take it up. The new battery's swift charging and discharging could help make possible the use of Li-ion batteries in applications such as electric cars.

To build the battery, materials science professor Gerbrand Ceder and graduate student Byoungwoo Kang at MIT synthesized a popular modern Li-ion battery material, LiFePO4 (Nature 2009, 458, 190).

The group used standard starting materials for preparing LiFePO4, but in slightly different amounts than usual. This method produced 50-nm-sized LiFePO4 particles, each coated with a glassy substance that's slightly depleted in iron and phosphorus atoms relative to the LiFePO4 bulk material.

Recent theoretical and experimental studies from several labs have shown that lithium ions travel speedily through battery material itself, but that the ions' ability to move across a surface—which depends on the arrangement of atoms on the surface—and into the bulk material may be the bottleneck.

The coating on their material, Ceder and Kang believe, solves that problem: The configurations of Li, O, and P atoms on the material's surface provide ready pathways for Li to migrate in and out of the surface rapidly.

"This is an important development because it provides a simple and inexpensive synthetic route to a high-quality active material for a well-established electrode system," says Thomas Richardson, a chemist and battery researcher at Lawrence Berkeley National Laboratory.

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Chemical & Engineering News
ISSN 0009-2347
Copyright © 2009 American Chemical Society


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