We often hear about the coming nanobot revolution, but just how are scientists planning on powering these future marvels? Well, researchers from Harvard and the University of Illinois may have found the solution in a 3D-printed battery: it's smaller than a grain of sand, yet has areal energy and power densities comparable to your cellphone battery. The team used a custom 3D printer with a 1mm wide nozzle to deposit two separate lithium metal oxide pastes into comb-like shapes, which then hardened to create an anode and cathode. After adding an electrolyte, a sub-hair-width cell was created with "performance comparable to commercial batteries in terms of charge and discharge rate, cycle life and energy densities." Those could someday wind up in medical devices, wearable electronics or tiny flying drones, for instance. To see how they did it, check the video after the break.