Singh and her colleagues mimicked a traditional Li-ion battery’s composition, which includes individual layers of thin metal coated with different active chemicals. In a normal battery, those layers are wrapped around one another and put in a canister. Singh figured the same principle should apply if the layers were painted onto a surface, so she got to work developing and testing spray paint versions of a normal battery’s cathode, anode, current collectors and polymer separator.
After tweaking the various formulas to make sure they would stick to whatever surface they were sprayed on, Singh and her colleagues got creative. They airbrushed batteries onto ceramic bathroom tiles, flexible pieces of plastic, glass, stainless steel and a beer stein.
In one experiment, they connected nine spray-battery-coated bathroom tiles and topped the arrangement with a small solar cell. After the solar panel had fully charged the battery tiles, they powered a set of lights that spelled “RICE” for six hours at a steady output of 2.4 volts. All of the various painted-battery devices performed consistently within 10 percent of the target capacity. They also withstood 60 charge-discharge cycles with only a small drop in capacity.