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Small Step on Nano Energy
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Written by Erik F. Hart   
Tuesday, 14 July 2009
In the assessment of the health of General Motors produced by the Obama administration in March, the company's investment in electric vehicles received a failing mark. "While the [Chevrolet] Volt holds promise," the report read, "it is currently projected to be much more expensive than its gasoline fueled peers and will likely need substantial reductions in cost in order to become commercially viable."

Electric vehicles have been hard pressed to compete with gasoline fueled cars thanks to one simple metric: energy density. The energy stored in 10 gallons of gasoline is equal to about 350 kWh. To hold that much energy in a standard lead acid battery would require 14 metric tons of storage. And while batteries using lithium chemistry are more energy dense, they are far more expensive.

In a result that might one day upend that arithmetic, researchers at the University of Maryland's NanoCenter have developed a way to store electric charge using nanoscale technology that can circumvent the limits of batteries. The promise of the breakthrough is that it can enable electricity to be stored and released as quickly and easily as gasoline, and at a comparable price.

Instead of a battery, which holds electricity in electrochemical form, the Maryland researchers have developed a new type of capacitor, which stores energy in the form of electric charge on a pair of opposing plates. Because the charge can be tapped directly, rather than through a chemical change, capacitors are able to supply large jolts of power, but for a limited time. In fact, the energy density of capacitors is lower than that of batteries.

To cram more energy into the same space, the research team started with a micrometer thick slice of aluminum riddled with even smaller pores. Over that porous surface, the researchers deposited an ultrathin layer of an insulating material and then covered that with another layer of metal. The result was a contorted sandwich that could hold as much as 10 times the electric charge of conventional metal insulator metal capacitors.

The research team, led by Gary Rubloff director of the Maryland NanoCenter, published their results in Nature Nanoteclmology.

The experimental device has a power density of 1 MW per kilogram, which ought to be sufficient to give an electric vehicle enough zip to be attractive. The reported energy density about 0.7 Wh per kilogram still trails far, far behind that of gasoline. But, the researchers write, "it should be possible to scale devices fabricated with this approach to make viable energy storage systems that provide both high energy density and high power density."

Whether this can be done quickly enough to save the Chevy Volt or let alone GM remains to be seen.
Last Updated ( Tuesday, 14 July 2009 )