US: Storing electricity on paper

The humble sheet of paper can be transformed into an effective battery with a coat of ink made of tiny carbon tubes and silver wires, a researcher at Stanford University has reported. It can even be crumpled up and still continue functioning as a battery.

The research, by assistant professor of materials science and engineering Yi Cui, used nanotechnology to create batteries and super-capacitors. The latter hold an electric charge for a shorter period of time than a battery but can store and discharge electricity more rapidly.

"Society really needs a low-cost, high-performance energy storage device, such as batteries and simple super-capacitors," Cui said in the Stanford Report. He said the nanomaterials used to create the paper batteries had very small diameters, which helped them stick strongly to paper, making the resulting battery or super-capacitor very durable.

The paper super-capacitor could last through 40,000 charge-discharge cycles - many more than lithium batteries. The nanomaterials also made ideal conductors because they moved electricity along much more efficiently than ordinary conductors, Cui said.

He had previously created nanomaterial energy storage devices using plastics but the new research showed that a paper battery was more durable because the ink adhered more strongly to paper. In addition, the paper devices could be crumpled or folded, or even soaked in acidic or basic solutions, without harming their performance.

Cui said a paper super-capacitor could be especially useful for applications such as electric or hybrid cars, which depended on the quick transfer of electricity. The paper super-capacitor's high surface-to-volume ratio also gave it an advantage.

"This technology has potential to be commercialised 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 said the technology's biggest impact could be in large-scale storage of electricity on the distribution grid. For example, excess electricity generated at night could be saved for peak-use periods during the day.

The work was reported in the paper Highly Conductive Paper for Energy Storage Devices, published in the Proceedings of the National Academy of Sciences.