Paper and nanotechnology combine to create a new kind of battery, reports Roger Highfield
What looks to the untrained eye like thick, black paper is a novel flexible battery that could offer new opportunities for tomorrow's gadgets, from self propelling paper planes to smart pockets that can recharge a mobile phone.
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Along with its ability to work in temperatures up to 150ºC (300ºF) and down to -70ºC (-100ºF), the battery can be printed like paper, rolled, twisted or folded, and even works with the help of human blood or sweat, so it could power implanted medical devices.
The battery's semblance to paper is no accident: more than 90 per cent of the device is made up of cellulose, the same plant cells used in most kinds of paper. "It's essentially a regular piece of paper, but it's made in a very intelligent way," said Prof Robert Linhardt of Rensselaer Polytechnic Institute, Troy, New York, one of the team that outlines the advance in the Proceedings of the National Academy of Sciences.
"We have discussed making paper airplanes that can power their own flight," he told The Daily Telegraph. "Or a shirt made from woven paper or cotton (also composed of cellulose) that could charge your cell phone simply by putting it in your pocket." He added that there are other applications of such lightweight batteries, pointing out that the US navy is looking at battery powered ships, and airforce battery powered planes.
To create the battery, the paper was infused with carbon nanotubes, so named because they consist of carbon atoms wrapped into tubes that only measure a few nanometres (billionths of a metre) across the mouth, which act as the battery electrodes and allow the storage devices to conduct electricity.
Using aluminium foil to pick up the current, the device can provide the long, steady power comparable to a conventional battery, as well as a quick burst of high energy typical of a device called a "supercapacitor."
Working with Prof Pulickel Ajayan and Prof Omkaram Nalamasu, the team used ionic liquid, a "liquid salt", as the battery's electrolyte. This lack of water allows the paper energy storage devices to withstand extreme temperatures.
The team also printed paper batteries without adding any electrolytes, and demonstrated that naturally occurring electrolytes in human sweat, blood, and urine can be used to activate the battery so it could be used in a pacemaker and for other medical uses.
Along with use in small hand-held electronics, the paper batteries' light weight could make them ideal for use in cars, aircraft, and even boats. The paper also could be moulded into different shapes, such as a car door, which the scientists believe could help pave the way towards novel engineering innovations.
However, the team has yet to develop a way to inexpensively mass produce the patented devices. The end goal is to print the paper using a roll-to-roll system similar to how newspapers are printed.
"When we get this technology down, we'll basically have the ability to print batteries and print supercapacitors," Prof Ajayan said. "We see this as a technology that's just right for the current energy market, as well as the electronics industry, which is always looking for smaller, lighter power sources."