June 19, 2013
Researchers Use 3D Printer To Make Sand Grain-Size Microbatteries
redOrbit Staff & Wire Reports - Your Universe Online
Researchers at Harvard University and the University of Illinois at Urbana-Champaign have successfully used 3D printing to make lithium-ion microbatteries the size of a grain of sand. The team said the printed microbatteries could eventually power tiny devices in fields ranging from medicine to communications, enabling the development of miniaturized medical implants, compact electronics, tiny robots and more.
"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 the study´s lead author Jennifer Lewis, a professor at Harvard´s School of Engineering and Applied Sciences and a core faculty member of the Wyss Institute for Biologically Inspired Engineering.
Researchers have invented many miniaturized devices in recent years, including medical implants, insect-like robots and tiny cameras and microphones that fit on a pair of glasses. But the batteries that power them are often as large or larger than the devices themselves, defeating the purpose of these microdevices.
To resolve this problem, manufacturers have typically deposited thin films of solid materials to build the electrodes. But such ultrathin designs mean solid-state microbatteries lack the energy to power next-generation miniaturized devices.
In the current study, the researchers realized they could pack more energy if they could create stacks of tightly interlaced, ultrathin electrodes that were built out of plane. To accomplish this, they turned to 3D printers, which follow instructions from three-dimensional computer drawings, depositing successive layers of material — inks — to create a physical object from the ground up, similar to stacking a deck of cards one at a time. Though still in its infancy, the technique is already being used in a variety of fields, from producing crowns in dental labs to rapid prototyping of aerospace, automotive and consumer goods — not to mention single-use guns.
Where Lewis' group went one step further was in designing a broad range of functional inks with useful chemical and electrical properties. They then used those inks with custom-built 3D printers to create precise structures with the electronic, optical, mechanical and biologically relevant properties they sought.
To print 3D electrodes, Lewis' group first created and tested several specialized inks. Unlike the ink in a traditional office printer which comes out as tiny drops of liquid that wet the page, the inks developed for extrusion-based 3D printing must satisfy two difficult requirements — they must exit fine nozzles like toothpaste from a tube, and they must immediately harden into their final form.
For the current study, the inks also had to function as electrochemically active materials to create working anodes and cathodes, and had to harden into layers as narrow as those produced by thin-film manufacturing methods.
To achieve this goal, the researchers created one type of ink for the anode with nanoparticles of a one type of lithium metal oxide compound and another 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. The researchers then 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, as well as 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," said Shen Dillon, an assistant professor in the department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign, who collaborated with Lewis on the study.
Wyss Foundation Director Donald Ingber said the study opens the door to a number of new microdevices.
"Jennifer's innovative microbattery ink designs dramatically expand the practical uses of 3D printing, and simultaneously opens up entirely new possibilities for miniaturization of all types of devices, both medical and non-medical. It's tremendously exciting.”
The results were published online Tuesday in the journal Advanced Materials.