Formation of thin films for a built-in power supply – Creation of thin-film lithium secondary batteries using a solid electrolyte

The power supply is an extremely important element in realizing next-generation sheet devices, as it needs to be formed as a small, thin-film device. In the case of conventional secondary batteries, there are still safety concerns, such as leakage of liquid electrolyte and the likelihood of fires caused by a short-circuit*1 occurring between electrodes during recharging because they use organic liquid electrolytes. For this reason, the project, under Research theme 3, attempts to develop safe, thin-film lithium secondary batteries which are free from such hazards as liquid leakage and/or fires, by employing electrolytes made from all-inorganic solid-state materials like glass or ceramics.

More specifically, materials suitable for a solid electrolyte, that is, those with high lithium ion conductivity and good thin-film formability, will be sought and developed. The project also aims to develop techniques for constructing optimal interfaces between the electrode current collector and the electrode active material and the electrolyte, where the solids are in contact with each other. In addition, efforts will be made to fabricate nanoparticles that can serve as a high-capacity electrode active material, and form both thin films (using film-forming methods including aerosol deposition*2) and transparent electrodes (using oxide nanoparticles). A combination of these development initiatives will allow the project to prototype and evaluate thin-film lithium secondary batteries that can be built or embedded into a flexible polymer substrate.

In this way, constituent technologies for realizing highly safe and reliable secondary batteries with high-capacity and long-life are expected to be developed and established. This is expected to lead to a wide range of applications in various other fields.

*1 A phenomenon in which dendritic or arborescent lithium deposits on the electrode by repeated charge and discharge cycles, causing the electrode to short out.
*2 A method of forming films at room temperature by spraying gas, in which nanoparticles are dispersed, onto a substrate inside the vacuum tank.

Establishment of constituent technologies for realizing all-solid-state
inorganic thin-film lithium secondary batteries