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Li-Ion Technology in Ink
Wednesday, December 11, 2013 | Printed Electronics World

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 3D 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 3D 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.

Lewis has taken two important steps toward printing electronic devices. First, she has invented an arsenal of what she calls functional inks that can solidify into batteries and simple components, including electrodes, wires, and antennas. Second, she has developed nozzles and high-pressure extruders that squeeze out the batteries and other components from an industrial-grade 3D printer. Lewis's inks use suspended nanoparticles of the desired materials, such as compounds of lithium for batteries and silver for wires.

These materials are mixed into a variety of solutions, and the resulting inks are nearly solid when unperturbed but flow when a certain amount of pressure is applied. Once printed, the materials return to solid form. Printing a battery from a single nozzle can take minutes, but Lewis's custom 3D printing technology can deposit inks from hundreds of nozzles at the same time.

The printing technology works at room temperature, not the high temperatures normally required to work with high-performing electronics. That makes it possible to print the materials on plastic without causing damage. The battery materials themselves aren't revolutionary, she says; "this is really more a revolution in the way things are manufactured."

Her printed lithium-ion batteries are as tiny as one millimeter square but perform as well as commercial batteries, because Lewis can render microscale architectures, and position structures with 100-nanometer accuracy, to mirror the structures of much bigger batteries.

Lewis's group holds eight patents for its inks and is working on licensing and commercializing the technology in the next few years. Although she says the initial plan is to provide tools for manufacturers, she may eventually produce a low-end printer for hobbyists.


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