Supercapacitors: Researchers Develop Manufacturing Technology to Produce Electrical Devices from Carbon Nanotubes

First discovered in 1991, carbon nanotubes have remained largely a laboratory curiosity. Now the GTRI researchers are out to change that by producing carbon nanotube-based devices for commercial applications.

Carbon nanotubes (CNTs) are a hexagonal network of carbon atoms rolled to form a seamless cylinder - a sort of "chicken wire" lattice of graphite. "This material has tremendous electrical, thermal and structural properties, however, few products utilizing CNTs have hit the commercial market," says Jud Ready, a research engineer in Georgia Tech Research Institute's (GTRI) Electro-Optics, Environment and Materials Laboratory.

Ready is developing a CNT-based electrochemical double-layer capacitor, a project sponsored by the U.S. Army Space and Missile Defense Command. Such supercapacitors would provide more power, increased energy density (more charge per gram of weight) and longer life than traditional batteries and capacitors that store electrical energy.

Ready's supercapacitors are made of two CNT-based active electrodes immersed in an electrolyte and separated by an ion-permeable membrane that prevents electron transfer. "CNTs are ideal to use as the active electrode material because their nanoscale dimensions provide more surface area for storing charge," Ready says. That extra surface area exponentially increases capacitance - the amount of power that can be stored.

Ready began work on the project last, aided by Stephan Turano, a materials science graduate student at Georgia Tech, and Charlie Higgins, a computer engineering major from Georgia State University. The team has already produced dozens of CNT supercapacitors, which have been used for electrical tests.

Feedback from those tests helps improve the manufacturing process. For example, the researchers have learned that when pressure is applied to electrodes during testing, the supercapacitor performs better. With that in mind, Ready is trying to incorporate a clamping or bolting between the two electrode plates during production to increase pressure.

The next step is reliability testing to see how the CNT supercapacitors hold up under different environments, which is especially important for space-based applications. The devices are placed in a chamber that exposes them to extreme temperature and humidity, accelerating the aging process. "We can simulate 20 years of life in about 1,000 hours instead of having them sit around for 20 years," Ready says.