Nanotech ink turns plain paper into a super battery

Researchers at Stanford University have developed a way to turn an ordinary sheet of paper into an ultra-lightweight and flexible battery by dipping it into an ink made with carbon nanotubes and silver nanowires.

The innovation offers a variety of promising uses, according to Yi Cui, an assistant professor of materials science and engineering.

“Society really needs a low-cost, high-performance energy storage device, such as batteries and simple supercapacitors,” said Cui, who published a paper on his research this week in the Proceedings of the National Academy of Sciences.

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,” 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 could 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 said.

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 (providing a new spin to the question, “Paper or plastic?”). In fact, the paper battery’s performance doesn’t degrade even when the material is crumpled, folded, or even soaked in acidic or basic solutions.

“We just haven’t tested what happens when you burn it,” Cui added.

The flexibility of paper allows for many clever applications.

“If I want to paint my wall with a conducting energy storage device, I can use a brush” Cui said.

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

Cui predicts the biggest impact could 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 could also require storage.