Credit: © 2007 National Academy of Science USA

With a growing demand for efficient batteries that can meet both the design and power needs of modern gadgets, researchers at Rensselaer Polytechnic Institute in the US have now made an efficient energy-storage device by combining cellulose — the main constituent of paper — with carbon nanotubes.

Pulickel Ajayan and colleagues1 grew vertically aligned multiwalled carbon nanotubes (MWNTs) on a silicon substrate and infiltrated them with a solution of cellulose dissolved in a so-called room-temperature ionic liquid. After solidification and removal of the excess liquid, the composite film was peeled from the substrate and was shown to possess excellent mechanical flexibility. When fabricated into a supercapacitor, the nanotubes acted as the working electrode, the cellulose as the spacer and the ionic liquid as the self-sustaining electrolyte. The device could charge/discharge over 100 cycles, showed a wider operating temperature range than commercial devices and could withstand temperatures down to 77 K (-196°C). Even electrolytes such as sweat, blood and urine were able to power up the device.

When fabricated into a battery, the composite could light up a tiny light-emitting diode. This flexible paper presents a cost-effective and efficient energy-storage material that can meet the stringent shape and size requirements of modern electrical devices.