Imagine a battery as flexible as paper—because it is made of paper. In August, a team at Rensselaer Polytechnic Institute in New York unveiled a small sheet of black paper that can store and discharge electricity. In addition to being light and flexible, it can extract electrical energy from human blood and sweat, making the device potentially usable as a power source for tiny medical devices inside the human body.
The RPI team made the paper battery by first growing an array of carbon nanotubes on a silicon surface and then covering the array in dissolved cellulose (the main constituent of paper). The cellulose forms a flexible sheet studded with embedded nanotubes that can be peeled away from the substrate. The nanotubes make the sheet as black as coal, but only a small quantity is needed. “Ninety percent of the device is still normal paper you buy at the store,” says Pulickel Ajayan, one of the lead researchers and a materials scientist. “The best part about this is its versatility,” he continues. “It’s paper. We can wrap a device in paper that also works as the device’s power source. Or we can slide it into a tiny crevice—anywhere, really. It is vastly superior to a conventional battery. If you cut a normal battery in half, you break it; it’s useless. If you cut a paper battery in half, you just make two batteries that have half the power of the original.” Want more power? Stack sheets of the paper together. “It’s not just a paper battery; it’s the ultimate battery,” Ajayan says.
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