US researchers announced they have successfully used the three-dimensional (3D) printing technique to print lithium-ion micro-batteries the size of a grain of sand.
The printed micro-batteries 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 power them, according to a research team from the Wyss Institute at Harvard University and the University of Illinois at Urbana-Champaign.
"Not only did we demonstrate for the first time that we can 3D- print a battery, we demonstrated it in the most rigorous way," senior author Jennifer Lewis of the Harvard University said in a statement.
To make the micro-batteries, the team had to print precisely interlaced stacks of tiny battery electrodes, each less than the width of a human hair, reported Xinhua.
The researchers 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 3D printing must fulfill two difficult requirements: they must exit fine nozzles like toothpaste from a tube and must immediately harden into their final form.
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.
In the end, the researchers created an ink for the anode with nano particles of one lithium metal oxide compound, and an ink for the cathode from nano particles of another.
The printer deposited the two 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.
The researchers said despite its tiny size, the battery's electrochemical performance is "comparable to commercial batteries" in terms of charge and discharge rate, cycle life and energy densities.
The findings were published online in the journal Advanced Materials.