Stanford scientists combine paper, ink and nanotubes to produce batteries

Stanford scientists are harnessing nanotechnology to quickly produce ultra-lightweight, bendable batteries and supercapacitors in the form of everyday paper. The research team led by Yi Cui, assistant professor of materials science and engineering, includes postdoctoral scholars Liangbing Hu and JangWook Choi, and graduate student Yuan Yang. Simply coating a sheet of paper with ink made of carbon nanotubes and silver nanowires makes a highly conductive storage device.

This method is not only small like the already demonstrated batteries made of nanotubes but it is also very cheap. 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.

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, which is at least an order of magnitude more than lithium batteries. 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. Furthermore, you can crumple or fold the paper battery, or even soak it in acidic or basic solutions, and the performance does not degrade.

The flexibility of paper allows for many clever applications. “If I want to paint my wall with a conducting energy storage device,” Cui said, “I can use a brush.” In his lab, he demonstrated the battery to a visitor by connecting it to an LED (light-emitting diode), 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.

“This technology has potential to be commercialized within a short time,” said Peidong Yang, professor of chemistry at the University of California-Berkeley. “I don’t think it will be limited to just energy storage devices,” he said. “This is potentially a very nice, low-cost, flexible electrode for any electrical device.”

Cui predicts the 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.

“The most important part of this paper is how a simple thing in daily life – paper – can be used as a substrate to make functional conductive electrodes by a simple process,” Yang said. “It’s nanotechnology related to daily life, essentially.”