If you tend to associate spray paint with nefarious behavior involving graffiti, prepare to have your mind blown. Scientists have invented batteries that can be spray painted onto any surface. Researchers at Rice University demoed the new technology by coating steel, glass, and a beer mug with painted-on batteries. "There has been a lot of interest in recent times in creating power sources with an improved form factor, and this is a big step forward in that direction," says a researcher.
The BBC dives into how the painted-on batteries work. Batteries are typically made of up five layers: a positive half, a negative half, and a separating material between, all sandwiched between two "current collectors." The researchers developed the optimal chemical blend for each layer, making use of carbon nanotubes along with a stickiness-inducing compound called poly-methylmethacrylate. The resulting concoction is just half a millimeter thick. (Read more battery stories.)