By making the basic building blocks of batteries out of ink, Harvard materials scientist Jennifer Lewis is laying the groundwork for lithium-ion batteries and other high-performing electronics that can be produced with 3-D printers. Although the technology is still at an early stage, the ability to print batteries and other electronics could make it possible to manufacture new kinds of devices. Think of self-powered biomedical sensors, affixed to the skin, that would continuously transmit vital signs to a smartphone. Or existing products could be made more simply and efficiently. For example, the plastic shell of a hearing aid is already 3-D printed for a custom fit inside a wearer’s ear. But the electronics are manufactured separately, and the batteries are often the type that must be replaced frequently. If the electronics and a rechargeable battery were printed together, the final product could be made more rapidly and seamlessly.