By dipping an ordinary piece of paper into ink infused with carbon nanotubes and silver nanowires, scientists have been able to create a low-cost battery or supercapacitor that is ultra-lightweight, bendable and very durable. The paper can be crumpled, folded or even soaked in acidic or basic solutions and still will work.
Stanford University scientist Yi Cui had previously created nanomaterial energy storage devices using plastics, but his new research showed that a paper battery is more durable because the ink adheres more strongly to paper. Coating a sheet of paper with ink made of carbon nanotubes and silver nanowires produced a highly conductive storage device that could be used in a multitude of applications.
"These nanomaterials are special," Cui said. "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 – 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 said.
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 by connecting it to an LED (light-emitting diode), which glowed brightly.
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. A paper supercapacitor has the advantage of a high surface-to-volume ratio and may be especially useful for applications like electric or hybrid cars, which depend on the quick transfer of electricity.
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, while wind farms and solar energy systems could also employ the new storage technology.
"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's work appears in the paper Highly Conductive Paper for Energy Storage Devices, published in the Proceedings of the National Academy of Sciences.
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