3D-printed pinhead battery could power robots.

One of the smallest batteries ever, this tiny lithium-ion can store enough juice to power tiny robots or medical implants.

We've seen some very sophisticated 3D-printed objects recently, but never a tiny 3D-printed battery -- one that's as small as a grain of sand, no less.

A group of U.S. and Korean researchers has managed to print a lithium-ion microbattery that can fit on the head of a pin.

Although it weighs less than 100 micrograms, it can store as much power per gram as larger Li-ion batteries used in laptops or electric vehicles. It could even power tiny robots or medical devices.

In a paper published in Advanced Materials, Harvard University's Jennifer Lewis and colleagues describe printing a "3D interdigitated microbattery architecture" with concentrated lithium oxide-based inks.

"Not only did we demonstrate for the first time that we can 3D-print a battery, we demonstrated it in the most rigorous way," Lewis said in a release.

The researchers made two interlaced, five-pronged electrodes by putting down up to 16 layers of lithium-metal-oxide particles. The pair measures less than a millimeter per side.

"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 collaborator Shen Dillon of the University of Illinois at Urbana-Champaign.

The batteries could be made bigger or in another shape to suit specific purposes, such as helping robotic insects fly.

Lewis has already made 3D-printed antennas, so it can't be too long until we start seeing swarms of printed robot bugs.

As if the real thing weren't bad enough. Check out the video below showing how the battery was printed.