3D Printed Tiny Batteries Pave the Way for Powering Miniaturized Devices

3D Printed Batteries

BOSTON—Scientists have turned to 3D printing to construct lithium-ion microbatteries the size of a grain of sand that enable miniaturized devices like medical implants and flying insect-like robots to now have a power source that is just the right size. To make the microbatteries, a team based at Harvard University's Wyss Institute and the University of Illinois at Urbana-Champaign printed precisely interlaced stacks of tiny battery electrodes, each less than the width of a human hair.

In the past, batteries that powered such miniaturized devices were as large or larger than the device itself, which defeated the purpose of building small. The printed microbatteries could supply electricity to tiny devices in fields from medicine to communications, including many that have lingered on lab benches for lack of a battery small enough to fit the device, but still provide enough stored energy to power them.

"Not only did we demonstrate for the first time that we can 3D print a battery; we demonstrated it in the most rigorous way," said Jennifer A. Lewis, professor at the Harvard School of Engineering and Applied Sciences (SEAS), and the senior author of the study, in a statement.

Lewis is the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard SEAS, and a Core Faculty Member of the Wyss Institute for Biologically Inspired Engineering at Harvard University. She led the project in her prior position at the University of Illinois at Urbana-Champaign, in collaboration with co-author Shen Dillon, an Assistant Professor of Materials Science and Engineering there.

Using a custom-built 3D printer, successive layers of ink were used to build the interlaced stack of electrodes to create the working anode and cathode of a microbattery. Lewis and her group designed a broad range of functional inks with useful chemical and electrical properties. And they have used those inks to create precise structures with the electronic, optical, mechanical, or biologically relevant properties they want.

To print 3D electrodes, Lewis's group first created and tested several specialized inks. Unlike the ink in an office inkjet printer, which comes out in droplets of liquid that wet the page, the inks developed for extrusion-based 3D printing must fulfill two difficult requirements. First, they must exit fine nozzles like toothpaste from a tube, and second, they must immediately harden into their final form.

In this case, the inks also had to function as electrochemically-active materials to create working anodes and cathodes, and they had to harden into layers that are as narrow as those produced by thin-film manufacturing methods. To accomplish these goals, the researchers created an ink for the anode with nanoparticles of one lithium metal oxide compound, and an ink for the cathode from nanoparticles of another. The printer deposited the inks onto the teeth of two gold combs, creating a tightly interlaced stack of anodes and cathodes. Then the researchers packaged the electrodes into a tiny container and filled it with an electrolyte solution to complete the battery. Next, they measured how much energy could be packed into the tiny batteries, how much power they could deliver, and how long they held a charge.

"The electrochemical performance is comparable to commercial batteries in terms of charge and discharge rate, cycle life, and energy densities," said Shen Dillon. "We're just able to achieve this on a much smaller scale."

Wyss Founding Director Donald Ingber, a professor of bioengineering at Harvard SEAS, called the news "tremendously exciting." The innovative microbattery ink designs, he said, "dramatically expand the practical uses of 3D printing, and simultaneously open up entirely new possibilities for miniaturization of all types of devices, both medical and non-medical."

The work was supported by the National Science Foundation and the DOE Energy Frontier Research Center on Light-Material Interactions in Energy Conversion. The results of the project were published in the June 17, 2013 online edition of the journal Advanced Materials and the print edition, volume 25, issue 33.

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