3D printing is great for building lifeless husks out of plastic, but soon we'll be able to start printing guts as well. Scientists have figured out how to coax a fully functioning lithium-ion battery out of nothing but some paste, and those small batteries could have big applications.

Developed by researchers from Harvard and the University of Illinois, each little power-pack is the size of a grain of sand and made up of two little comb-shaped bits of lithium metal oxide pastes which are then hardened, interlaced, and dunked in a tiny container full of electrolyte solution. The result is a battery that's not only 3D printable, but also as good as a tiny mobile phone battery, with similar charge rates, power density, and cycle life.

Tiny batteries have existed before, but the size has always come at a cost. Medical implants, and other miniaturised devices have already started blowing past what existing micro-batteries can handle. And being able to 3D print these suckers makes production a breeze, once you have the right setup. Now we just need to figure out those graphene batteries and we'll be all set. [Harvard via Engadget]