This image released by the Rensselaer Polytechnic Institute shows a sample of the new nanocomposite paper developed by researchers at Rensselaer Polytechnic Institute. Infused with carbon nanotubes, the paper can be used to create ultra-thin, flexible batteries and energy storage devices for next-generation electronics and implantable medical equipment. [Photo: AFP/HO/Victor Pushparaj]

by Louise Daly

CHICAGO (AFP) - US researchers said Monday they have invented a lightweight paper battery that could serve as an enhanced power storage device for the next generation of consumer electronic devices.

The battery produces electricity in the same way as the conventional lithium-ion batteries that power so many of today's gadgets, but all the components have been incorporated into a lightweight, flexible sheet of paper.

An early prototype of the device, just big enough to be held between thumb and forefinger, kicks out 2.5 volts, enough juice to power a small fan, or illuminate a light, and its inventors say the battery can be easily scaled up to provide enough power to run any number of electronic gadgets.

"You can stack one sheet on top of another to boost the power output," said Robert Linhardt, a biology and chemistry professor at Rensselaer Polytechnic Institute in Troy, New York, and a project team member.

"We've already experimented with 10 sheets, but there's nothing to stop you using 500, and they can be rolled, bent or folded into any shape or space you like. There are endless design possibilities."

As manufacturers strive to pack more functionality into smaller and smaller devices, the pressure is on to shrink components as much as possible, but in many cases the battery is still the bulkiest part of any electronic device.

The Rensselaer scientists substituted tiny carbon filaments or nanotubes for the electrodes used in a conventional battery and used an ionic liquid solution as an electrolyte -- the two components that conduct electricity.

They used the cellulose or paper as a separator -- the third essential component of a battery.

"It's a single, integrated device," said Linhardt. "The components are molecularly attached to each other: the carbon nanotube print is embedded in the paper and the electrolyte is soaked into the paper. The end result is a device that looks, feels, and weighs the same as paper."

The device can function in temperatures of 300 degrees Fahrenheit and down to 100 below zero, and was engineered to function as both a battery and a supercapacitor, a device that charges almost instantaneously and is often used for industrial applications.

Beyond laptop computers, cellphones or digital cameras, the paper batteries would be ideal for use in automobiles, aircraft and even boats because of their light weight, the researchers said. The device is 90 percent cellulose.

"The paper could also be molded into different shapes, such as a car door, which would enable important new engineering innovations.

The materials used in the prototype are inexpensive but the team is still working on ways to mass produce the paper battery cheaply. They hope that eventually they can print the paper using a roll-to-roll system similar to how newspapers are printed.

The researchers reported the details of their invention in a paper that appears in the Proceedings of the National Academy of Sciences.