Micro-Supercapacitors Will Power Electronic Devices

Published on Thursday April 22, 2010

Energy storage devices developed by Drexel University researchers may one day greatly improve the longevity of mobile phones, laptop computers, and other battery-powered devices.

A paper in the April 23, 2010 issue of Science magazine[1] by John Chmiola (MSE Ph.D. 2009), his advisor Yury Gogotsi, and their collaborators in France, describes a new method of producing supercapacitors that doubles their performance over similar devices reported so far. 

Supercapacitors, also called electric double layer capacitors or ultracapacitors, store energy through reversible ion adsorption at high surface area electrodes usually made of carbon, in contrast with batteries, which store electrical energy in chemical bonds in a bulk material.  This difference allows supercapacitors to charge and discharge faster, recharge a near infinite number of times, and operate at a wider temperature range with high efficiency.  Supercapacitors are built of environmentally friendly materials, such as carbon, aluminum and polymers. 

Chmiola and his co-authors use an electrode material called carbide-derived carbon (CDC), in which metal atoms are etched from a metal carbide, such as titanium carbide (TiC), to form a porous carbon with very high surface area.  

Previous studies by this group used CDC in powdered form[2].  The innovation reported here is the use of "bulk" thin films.  The team took some cues from the microelectronics industry, starting with conductive TiC substrates, then etching a very thin electroactive layer (Ti-CDC) to store charge.

"In the traditional sandwiched construction, the electroactive materials that store the charge are loosely held together particles pressed onto some metal that transports electrons to and away from these materials and separated by some other material that keeps the individual electrodes from shorting to one another," Chmiola said.  "The whole sandwich is then rolled up and put in a little soda can or plastic bag."

By using microfabrication-type techniques, Chmiola and his colleagues avoided many of the pitfalls of the "sandwich" method, such as poor contact between electroactive particles in the electrode; large void space between the particles, which contributes significantly to mass and volume because it is filled with electrolyte, but does not store charge; and poor contact with the materials that carry electrons out of the electroactive materials and to the external circuitry.

Chmiola received National Science Foundation (NSF) IGERT and Graduate Research Fellowships for his Ph.D. studies, and is now a post doctoral researcher in the Environmental Energy Technologies Division at Lawrence Berkeley National Laboratory.  This is his second paper in Science magazine.

This news has been featured in MIT Technology Review, AZoNano.com, Physorg.com, and Popular Science.

1. J. Chmiola, C. Largeot, P.-L. Taberna, P. Simon, and Y. Gogotsi. Monolithic carbide-derived carbon films for micro-supercapacitors, Science (2010).

2. J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, P.L. Taberna. Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer, Science (2006).

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