​Solid-electrolyte lithium-ion batteries are not new. Until now, however, they had never been miniaturized. The batteries offer a number of advantages: For one, they cannot leak or explode. They also offer low self-discharge, which means that they can be stored for longer without losing their charge. 

The researchers used conventional silicon microelectronics processes to deposit the solid electrolyte in ultra-thin layers around a micron thick. They used Leti's 200 mm production equipment to complete the photolithography step, deposit the electrolyte onto the silicon substrate, and etch the layers. The main challenge was to adapt these processes to battery materials. The use of a silicon substrate will facilitate the subsequent integration of the microbatteries into electronic systems like MEMS. 

The battery obtained is very small (around 1.7 mm x 3.1 mm x 0.1 mm) and offers a capacity of 25 µAh. When coupled with an induction charging or vibration-based energy-harvesting system it can be used for very-low-power applications in the healthcare field. Another project is currently underway with a manufacturer to combine the battery with an intraocular pressure sensor for glaucoma monitoring. In 2019 the technology won the Best Technical Development within Energy Storage Award from IdTechEx.