Bing Hu, a post-doctoral student, prepares a small square of ordinary paper with an ink that will deposit nanotubes on the surface that can then be charged with energy to create a battery. (Stanford University/L.A. Cicero)

Using nanotechnology, Stanford scientists are producing ultra-lightweight, bendable batteries and supercapacitors in the form of everyday paper. Coating a sheet of paper with ink made of carbon nanotubes and silver nanowires makes a highly conductive storage device.

Like batteries, capacitors hold an electric charge, but for a shorter period of time. However, capacitors can store and discharge electricity much more rapidly than a battery.

"These nanomaterials are special," said Yi Cui, assistant professor of Materials Science and Engineering. "They're a one-dimensional structure with very small diameters."

The small diameter helps the nanomaterial ink stick strongly to the fibrous paper, making the battery and supercapacitor very durable. The paper supercapacitor may last through 40,000 charge-discharge cycles. The nanomaterials also make ideal conductors because they move electricity along much more efficiently than ordinary conductors.

Cui had previously created nanomaterial energy storage devices using plastics. His new research shows that a paper battery is more durable because the ink adheres more strongly to paper. Even when crumpled, folded, or soaked in acidic or basic solutions, the performance of the paper battery does not degrade.

The flexibility of paper allows for many clever applications. In Cui's lab, he demonstrated the battery to a visitor by connecting it to an LED, which glowed brightly.

A paper supercapacitor may be especially useful for applications like electric or hybrid cars, which depend on the quick transfer of electricity. The paper supercapacitor's high surface-to-volume ratio gives it an advantage.

Cui predicts the technology's biggest impact may be in large-scale storage of electricity on the distribution grid. Excess electricity generated at night, for example, could be saved for peak-use periods during the day. Wind farms and solar energy systems also may require storage.

In the video below, post-doctoral students in Cui's lab light up a diode from a battery made from treated paper. The paper batteries are treated with a nanotube ink, and baked and folded into electrical generating sources like foil.

(Stanford University)