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 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
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
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.
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).