Under a bench at Sang-Young Lee’s lab is an ordinary, somewhat beat-up ink-jet printer he has modified so that it spits out electronic circuits and a type of energy storage device called a supercapacitor. To make it work, Lee empties the ink cartridges and refills them with specially formulated battery materials and conductive inks. When loaded with treated paper, his hacked printers make flexible, durable supercapacitors and simple circuit components in the form of a high-resolution map of the Republic of Korea, a flower, a logo, or any other desired design.

Lee, a battery chemist at the Ulsan National Institute of Science and Technology (UNIST) in South Korea, has been working on flexible printed batteries for the past five years. “The architecture of the battery hasn’t changed since the birth of the lithium-ion battery,” he says. Energy-storing materials are cast onto metal foil and packaged with a liquid electrolyte into a few basic shapes—pouches, coins, cylinders, and rectangular prismatic cells. For example, the design of wearable health monitors, whether they’re in textiles or worn in a wristband, is constrained by the need for a battery box or pouch. Instead, Lee wants to make flexible batteries that disappear into a design and can be made using simple equipment, such as an ink-jet printer.

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