A new battery developed by researchers at Brown University (Providence, RI) uses plastic, not metal, to conduct electrical current. The hybrid device marries the power of a capacitor with the storage capacity of a battery.

“Batteries have limits,” says Tayhas Palmore, an associate professor at Brown’s division of engineering. “They have to be recharged. They can be expensive. Most of all, they don’t deliver a lot of power. Another option is capacitors. These components, found in electronic devices, can deliver that big blast of power. But, they don’t have much storage capacity.”

Palmore and her colleagues decided to combine elements of both a battery and a capacitor. They began to experiment with a new energy-storage system using a substance called polypyrrole, a chemical compound that carries an electrical current. Discovery and development of polypyrrole and other conductive polymers netted three scientists the 2000 Nobel Prize in chemistry.

In their experiments, the researchers took a thin strip of gold-coated plastic film and covered the tip with polypyrrole and a substance that alters its conductive properties. The process was repeated using another kind of conduction-altering chemical. The result was two strips with different polymer tips. The plastic strips were then stuck together, separated by a papery membrane to prevent a short circuit.

Like a capacitor, the hybrid battery can be rapidly charged, then discharged to deliver power. Like a battery, it can store and deliver that charge over long periods of time.

During testing, the new battery performed like a hybrid, too. It had twice the storage capacity of an electric double-layer capacitor. And, it delivered more than 100 times the power of a standard alkaline battery.

In width and height, the new battery is smaller than an iPod Nano. It’s also thinner; about as slim as an overhead transparency.

“You can create batteries everywhere out of it,” says Palmore. “You could wrap cell phones in it or electronic devices. Conceivably, you could even make fabric out of this composite.”

However, some performance problems, such as decreased storage capacity after repeated recharging, must be overcome before the device is marketable. But, Palmore expects strong interest, because battery makers are always looking for new ways to more efficiently store and deliver power. NASA and the U.S. Air Force are also exploring polymer-based batteries.

“What we’ve got is a good concept,” claims Palmore. “Put electroactive molecules into conducting polymers and you can come up with all sorts of interesting materials that store energy.”