A tiny new battery that packs an energy punch could power more compact next-gen pacemakers and other medical devices. The LiCoO2 battery was developed by researchers at CEA-Leti, part of the French atomic energy agency. Battery chemist Sami Oukassi says it has a higher energy density than any thin-film battery reported so far. The battery is just 3.10 by 1.70 mm in area—which doesn’t leave much room for energy-storing electrode materials. Oukassi says his group improved the thin-film battery’s performance by making a thicker layer of LiCoO2 at higher yield. Thin-film batteries generally use less than 10 µm of the material; the CEA-Leti group was able to double this value while still achieving good-quality films that provide an easy path for charge-carrying lithium ions. “We developed advanced patterning methods for this material—usually you can’t do that on lithium,” Oukassi says. That enabled the team to make a prototype battery that meets the energy requirements for prototype medical devices such as disease-monitoring smart contact lenses. Oukassi, who described the research at the International Electron Devices Meeting in San Francisco in December, says the group hopes to encapsulate the battery so that it is safe for use in future wearable and implantable medical devices.