Better rechargeable batteries inmaking

Better rechargeable batteries in the making

12:53 AM, 15th November 2011
Better rechargeable batteries in the making

EVANSTON, US: Imagine a cellphone battery that stayed charged for more than a week and recharged in just 15 minutes. That dream battery could be closer to reality thanks to Northwestern University research.

A team of engineers has created an electrode for lithium-ion batteries - rechargeable batteries such as those found in cellphones and iPods - that allows the batteries to hold a charge up to 10 times greater than current technology. Batteries with the new electrode also can charge 10 times faster than current batteries. The researchers combined two chemical engineering approaches to address two major battery limitations - energy capacity and charge rate - in one fell swoop. The technology could pave the way for more efficient, smaller batteries for electric cars. The technology could be seen in the marketplace in the next three to five years, the researchers said.

A paper describing the research is published by the journal Advanced Energy Materials.“We have found a way to extend a new lithium-ion battery’s charge life by 10 times,” said Harold H Kung, Lead Author of the paper. “Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium-ion batteries on the market today.” Kung is Professor of chemical and biological engineering in McCormick School of Engineering and Applied Science.

Currently, the performance of a lithium-ion battery is limited in two ways - energy capacity and battery’s charge rate. In rechargeable batteries, the anode - made of layer upon layer of carbon-based graphene sheets - can only accommodate one lithium atom for every six carbon atoms.

Presently, the speed of a battery’s charge rate is hindered by the shape of graphene sheets: they are extremely thin, but very long. Lithium ion takes long to travel to the middle, creating a sort of ionic traffic jam around edges of the material.

Kung’s research team has combined two techniques to combat both these problems. First, they sandwiched clusters of silicon between the graphene sheets. This allowed for a greater number of lithium atoms in the electrode while utilizing flexibility of graphene sheets to accommodate silicon volume changes.

“We have much higher energy density because of silicon and sandwiching reduces capacity loss caused by silicon expanding and contracting. Even if silicon clusters break up, silicon won’t be lost,” said Kung.

Kung’s team also created miniscule holes (10 to 20 nanometre) in the graphene sheets, termed “in-plane defects.” This reduced time it takes the battery to recharge by up to 10 times.

This research was all focused on the anode; next, the researchers will begin studying changes in cathode. They will also look into developing an electrolyte system that will allow the battery to automatically and reversibly shut off at high temperatures.

The Energy Frontier Research Center program of the US Department of Energy, Basic Energy Sciences, supported the research. Other authors of the paper are Xin Zhao, Cary Hayner and Mayfair Kung, all from Northwestern.

(C) Northwestern University News

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