Run out of batteries? Just spray-paint some new ones.

Researchers have created five sprayable paints that form a lithium-ion battery when layered together, letting you store energy on walls, tiles or even your favourite mug. Regular batteries contain a positive and negative electrode, both paired with a metal current collector, and a polymer separator sandwiched in the middle. These five layers are normally manufactured in sheets and rolled up into a cylinder, making it hard to create extremely thin batteries. Now, Neelam Singh and colleagues at Rice University in Houston have used a combination of existing metallic paints and custom materials to create sprayable versions of each layer, allowing them to make batteries just a fraction of a millimetre thick by airbrushing the layers onto a surface, one at a time.