3D printing can be used to print lithium-ion micro-batteries the size of a grain of sand which could sufficiently power miniature devices, reveals a study from a team of scientists at Harvard University and the University of Illinois at Urbana-Champaign.
To make the micro-batteries, the team printed precisely interlaced stacks of tiny battery electrodes, each less than the width of a human hair.
Manufacturers have until now generally had to use solid-state batteries, created by depositing films of solid materials to build the battery electrodes. These batteries were often as large, or larger, than the devices themselves, defeating the purpose of miniaturisation. The solution was to design ultra-thin solid-state batteries, which then proved insufficient in powering the tiny devices.
The scientists in the study realised they could shove more energy into a micro-battery by creating stacks of tightly interlaced, ultrathin electrodes that were planar-built, for which they turned to 3D printing.
“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, senior author of the study and Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences (SEAS).
Three-dimensional computer drawings provide instructions to 3D printers, which then work by depositing successive layers of material – inks – to build a physical object from the ground up, much like stacking a deck of cards, one card at a time. The technique is used in a range of applications, from producing crowns in dental labs to rapid prototyping of aerospace, automotive and consumer goods.
Lewis’ team took the technique a step further by designing a broad range of ‘functional’ inks – inks with useful chemical and electrical properties. The team used these inks in custom-built 3D printers to create precise structures with relevant electronic, optical, mechanical or biological properties.
The team had to create and test several specialized inks. Unlike the ink in an office inkjet printer, which comes out in drops of liquid that sink into a page, the ink developed for extrusion-based 3D printing needs to satisfy two difficult requirements. It must first be able to exit fine nozzles like toothpaste from a tube, and then harden into its final form.
In this case, 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 accomplish these goals, the researchers created inks for the anode and cathode, which the printer then deposited 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. A researcher on the team pointed out that the electrochemical performance is comparable to commercial batteries in terms of charge and discharge rate, cycle life and energy densities, but on a much smaller scale.
“Jennifer’s innovative micro-battery ink designs 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. It’s tremendously exciting,” said Donald Ingber, Wyss Founding Director and Bioengineering Professor at Harvard SEAS.
Engineers in fields ranging from medicine to communications are continuously inventing miniaturized devices, including medical implants, flying insect-like robots, and tiny cameras and microphones that fit on a pair of glasses, that all require tiny yet efficient batteries.