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Viable li-ion microbatteries are the size of a grain of sand

19 June 2013

A novel application of 3D printing could enable the development of miniaturised medical implants, compact electronics, tiny robots, and more.

The interlaced stack of electrodes were printed layer by layer to create the working anode and cathode of a microbattery (image: courtesy of the researchers)
The interlaced stack of electrodes were printed layer by layer to create the working anode and cathode of a microbattery (image: courtesy of the researchers)

3D printing can now be used to print lithium-ion microbatteries the size of a grain of sand, which 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, yet provide enough stored energy to power them.

To make the microbatteries, a team based at Harvard University 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.

"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 Lewis of Harvard University. Dr Lewis led the project in her prior position at the University of Illinois at Urbana-Champaign, in collaboration with co-worker Shen Dillon.

In recent years engineers have invented many miniaturised 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 or larger than the devices themselves, which defeats the purpose of miniaturisation.

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

The scientists determined that they could pack more energy if they could create stacks of tightly interlaced, ultra-thin electrodes that were built out of plane. For this they turned to 3D printing, using a broad range of functional inks with useful chemical and electrical properties.

To print 3D electrodes, Lewis' group first created and tested several specialised inks that could exit fine nozzles and 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 on 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. We're just able to achieve this on a much smaller scale," Dillon said.

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