NB: sul NYT nel 2011…
vedere anche ScienceDirect.
Source : New York Times
Batteries That Can Multitask
THERE’S more than meets the eye in the battery-powered model car sitting in Emile Greenhalgh’s laboratory at Imperial College London.
The model has been modified by the researcher’s team to increase the amount of electrical energy it can store — but not by installing a bigger battery. Instead, the team added body components that double as capacitors, devices that hold an electrical charge until they are tapped.
“Although the energies they provide are fairly modest,” Dr. Greenhalgh, a composites expert, said, “they have shown that our material could be used to smooth the demands on the battery, thus enhancing its life.”
Designers of full-scale electric vehicles are working toward the same goal: battery reserves need to be extended because today’s technology typically delivers only enough power for about 100 miles of driving. Larger batteries are not necessarily the solution, either. Even the most advanced designs weigh hundreds of pounds, reducing the vehicle’s range.
To help cut weight and increase driving distances, engineers are developing car frames and bodies made of carbon fiber-reinforced composites, plastic materials that can be 50 percent lighter than steel but provide superior strength and rigidity. Although used in a handful of exotic sports cars, carbon composites remain too costly for mass-market cars.
One potential solution is to build autos with carbon composites that can also serve as batteries. The dual-function materials could make E.V.’s and hybrid vehicles lighter as they simultaneously provide extra electricity.
“Structural power technology combines mechanical structure and energy storage capabilities,” said Dr. Greenhalgh, who heads a group at the college working on the concept. “This could allow us to have our cake and eat it too.”
To enable the composite materials to store electricity, the resin that binds the carbon fibers is laced with lithium ions; the fibers serve as conductive electrodes for this type of charge-holding capacitor.
It is different from a battery, which produces electricity from a chemical reaction. Another research group, at the Swedish Institute of Composites, is working on a structural battery.
Dr. Greenhalgh also leads a wider European Union project, which includes Volvo Cars, to study the innovative materials. “Volvo says that structural power technology will be key to the E.V.’s they’re developing,” he said.
One of the project’s goals is to test a prototype E.V. with a trunk floor that provides electricity. “We’re expecting a 15 percent weight savings compared to the standard battery in a conventional structure,” said Per-Ivar Sellergren, an engineer at the Volvo Cars Materials Center in Gothenburg, Sweden.
“Even though the panel will not be large enough to power the entire car, it could provide enough power to switch the engine off and on when the car is stopped at a traffic light,” he said.
Mr. Sellergren said that if future composite battery structures could store energy as efficiently as lithium-ion batteries, an E.V. would require only the roof, hood and trunk lid to be made of such materials to achieve an 80-mile range.