Storing Power in a Sheet of Paper

The photograph taken by Victor Pushparaj is curtasy of Rensselear Polytechnical Institute.

Researchers at Rensselaer Polytechnic Institute have developed a new energy storage device that easily could be mistaken for a sheet of black paper. Along with its ability to function in 300F to -100F temperatures, the device is completely integrated and can be printed like paper.

More than 90% of the device is made up of cellulose, the same plant cells used in paper. The researchers infused this paper with aligned carbon nanotubes, which give the device its black color. The nanotubes act as electrodes and allow the device to conduct electricity. Engineered to function as both a Li-ion battery and a supercapacitor, the device provides the long, steady power output of a conventional battery and a supercapacitor’s quick burst of high energy. The device can be rolled, twisted, folded, or cut into shapes with no loss of mechanical integrity or efficiency. The batteries can also be stacked, like a ream of printer paper, to boost the total power output.

The researchers used ionic liquid, a liquid salt, as the battery’s electrolyte. Since ionic liquid contains no water, there’s nothing in the batteries to freeze or evaporate. The team also printed paper batteries without electrolytes, and demonstrated that naturally occurring electrolytes in human sweat, blood, and urine can activate the device. Since paper is extremely biocompatible, these new hybrid battery/supercapacitors have potential as power supplies for devices implanted in the body.

The materials to create the paper batteries are inexpensive, but the team is still investigating ways to inexpensively mass produce the devices. The goal is to print the paper using a roll-to-roll system similar to newspaper printing.