To make the microbatteries, the researchers printed precisely interlaced stacks of tiny battery electrodes, each less than the width of a human hair.
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 building small. 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 contain sufficient energy to power tomorrow's miniaturised devices.
The scientists realised they could incorporate more energy if they could create stacks of tightly interlaced, ultrathin electrodes that were built out-of-plane. For this they turned to 3D printing. The researchers have designed a broad range of functional inks—inks with useful chemical and electrical properties. And they have used those inks with their custom-built 3D printers to create precise structures with the electronic, optical, mechanical, or biologically relevant properties they want.
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 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. The electrochemical performance is claimed to be comparable to commercial batteries in terms of charge and discharge rate, cycle life and energy densities.