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JUL/AUG 2013  

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Printing micro batteries

For the first time, a research team from the Wyss Institute at Harvard University and the University of Illinois at Urbana-Champaign demonstrated the ability to 3-D print a lithium-ion battery the size of a grain of sand.


The printed microbatteries could supply electricity to tiny devices in the medical and communications industries, according to the Wyss Institute.

To make the microbatteries, the research teams printed precisely interlaced stacks of tiny battery electrodes, each less than the width of a human hair.

In recent years engineers have invented many miniaturized devices, including medical implants, flying insect-like robots and tiny cameras and microphones that fit on a pair of glasses. But often the batteries that power them are as large as the devices themselves, which defeats the purpose of building small devices.

To get around this problem, manufacturers have traditionally deposited thin films of solid materials to build the electrodes. However, due to their ultrathin design, these solid-state micro-batteries do not pack sufficient energy to power tomorrow’s miniaturized devices.

The scientists realized they could pack more energy if they could create stacks of tightly interlaced, ultrathin electrodes that were built out of plane. For this they turned to 3-D printing. 3-D printers follow instructions from 3-D computer drawings, depositing successive layers of material to build a physical object from the ground up, much like stacking a deck of cards one at a time.

lewisbattery

This image shows the interlaced stack of electrodes that were 3-D printed layer by layer to create the working anode and cathode of a microbattery. Credit: Ke Sun, Teng-Sing Wei, Jennifer Lewis, Shen J. Dillon

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

The project is led by Jennifer Lewis, Ph.D., senior author of the study, who is also the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences, and Shen Dillon, an assistant professor of Materials Science and Engineering at the University of Illinois at Urbana-Champaign.

The results were published in a recent online edition of Advanced Materials.