Los Alamos Researchers Charge Ahead In Ultracapacitors

Breakthroughs in active material development and ultracapacitor device packaging were revealed today at the national meeting of the American Chemical Society in Anaheim, Calif. by Steven Shi, a researcher in the Material Sciences and Technology Division at Los Alamos.

Building upon an existing research patent in conducting polymers, Los Alamos scientists have created a new single-cell ultracapacitor with high energy density -meaning it can hold a lot of energy in a small volume. The prototype ultracapacitor is the size of a dime and contains microscopic carbon fibers specially coated with conducting polymer to act as charge-storage material.

According to Shimshon Gottesfeld, leader of the research team, "This is a very exciting advancement for us. Achieving 2.7 million charge/discharge cycles is a leap forward in the development of this new generation of ultracapacitors. I'd say we're well on our way to developing a product that has significant commercial value."

In one sense, ultracapacitors lie somewhere between a battery and a capacitor. Conventional batteries provide stored energy for extended periods of time, but have peak-power and cycling limitations. Because of chemical reactions that occur within the battery, they have limited ability to charge and discharge energy repeatedly and quickly.

Conventional capacitors are capable of repeatedly providing high levels of power, but can hold very little energy. As a result, they often cannot discharge this power for more than a few microseconds.

Ultracapacitors store high levels of energy in a small volume and then release that energy in power bursts. In an automobile application, for example, a vehicle might use this burst of power to accelerate or climb a hill. Because ultracapacitors move electrical charges between conducting materials, rather than perform any chemistry, they maintain an ability to cycle far longer than batteries. Ultracapacitors, by design, are lighter and smaller than batteries with comparable peak-power levels.

The new ultracapacitor was created at Los Alamos by electroplating a unique conducting polymer material onto the carbon fibers of a small, paper-thin disk, covering the active material with a porous separator and adding electrolytic solution before sealing the device.

According to Shi, "In many applications, ultracapacitors are superior to both batteries and conventional capacitors. You can cycle (recharge) them millions of times without any loss of performance. Because there's no chemical reaction, they don't deteriorate and you'll probably rarely need to replace them."

The advantage of the Los Alamos ultracapacitor over other ultracapacitors currently in development, or on the market, is its large surface area, achieved while maintaining an open structure that allows fast shuttling of ions. This open structure combined with high surface area allows for higher electronic and ionic connectivity between the active material and the electrolyte.

The active materials used in the Los Alamos ultracapacitor are the result of a steady collaboration with chemical researchers at the University of Texas in Dallas. According to Gottesfeld, "John Ferraris and the University of Texas-Dallas team have been with us from Day One. Their expertise in the field of organic chemistry has been critical to the development of this ultracapacitor."

Shi believes his group's latest successes in ultracapacitors are only the beginning of the story. "I think we can make these ultracapacitors even better," said Shi. "In the future we should be able to increase the ultracapacitor's energy density to four or five times its current level."

Gottesfeld agrees, "The future applications for this technology are very significant. In any situation where you need repeated bursts of power to an electrical device, like a motor or a cellular phone, the ultracapacitor would work well."

The conducting polymer ultracapacitor is the work of Los Alamos researchers Shimshon Gottesfeld, Xiaoming Ren, Steve Shi and John Davey.

Los Alamos National Laboratory is operated by the University of California for the Department of Energy.