New Micro-Supercapacitors

August 17, 2010

I’ve written here a number of times about new developments in energy storage technology.  Improvements in this area are of great importance, both to facilitate the use of renewable energy sources (because the wind does not always blow, nor does the sun always shine), and to improve the performance and range of electric vehicles.

Recent articles, at the and Ars Technica, describe a new super-capacitor technology developed by a research team from the US and France.   The team’s work is described in a letter published in the journal Nature Nanotechnology [abstract].  As you may recall from physics class, the most basic capacitor is just two conductive plates separated by an insulator.  The larger the area of the plates, the larger the electrical charge that can be stored.  For this reason, activated carbon is sometimes used in supercapacitors, because it has a very high ratio of surface area to volume.  The research team took a slightly different approach, and used “onion-like carbon” [OLC] as an electrode material; in OLC, the individual particles of the material are made up of concentric spheres of carbon atoms, giving a total particle size of 6-7 nm.  The particles are deposited on an electrode substrate by electrophoresis.

The team found that activated carbon supercapacitors had higher capacitance than the new-deisgn “micro supercapacitors” of the same electrode size, by a modest amount.  But the new devices had a discharge rate (= energy delivery rate) about ten times higher (at about 200 volts/second), and a power density about 100 times as great as the activated carbon devices.  The devices could easily find an application niche:

Compared to a thin film lithium battery, its energy per volume is an order of magnitude lower, but its power is over 10,000 times higher. In the paper’s final graph, which compares these two measures, the authors show that the device is the only one with this sort of performance, which means that OLC could find a home for applications that require large bursts of power, long lifetimes, and a decent storage capacity.

There are still improvements that can be made with these devices, but it is a hopeful sign that significant progress can be made.

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