The problem that has stood in the way of 3D-printed lithium-ion batteries (at least, until now) is that the polymers traditionally used in this kind of printing aren't ionic conductors. The goal was to find a way to print custom-sized lithium-ion batteries in a cost-effective way using a regular, widely available 3D printer.
In order to make the batteries conductive, the team led by Christopher Reyes and Benjamin Wiley infused the polylactic acid (PLA) usually used in 3D printing with an electrolyte solution. The researchers also incorporated graphene and carbon nanotubes into the design of the case to help increase conductivity. After these design modifications, the team was able to 3D print an LED bracelet, complete with a custom-sized lithium-ion battery.
It's important to note that this research is very preliminary; the battery was only able to power the bracelet for about 60 seconds. The team notes that the capacity of the printed battery is well below commercial standards. But they have ideas for how to improve capacity, and this idea has a lot of promise for the future of small gadgets and tech.