Empa researchers have achieved a milestone in the search for a solid electrolyte, the conductive medium for future solid-state batteries. On the one hand, this material must be highly conductive for lithium ions, and on the other hand manufacturing costs should be as low as possible. Ultra-thin layers of a special ceramic (chemically speaking, Li7La3Zr2O12) should make the production of high-performance solid-state batteries possible in the near future.
Lithium-ion batteries may pose a risk because of the flammable liquid inside them. However, this electrolyte could be replaced in future by an incombustible, heat-resistant solid. In addition to the improved safety of such batteries, a better performance and a longer service life would be major advantages.
Yaroslav Romanyuk’s research team at Empa is focusing on thin-film technologies for the development of these new solid-state batteries. The electrolyte in such a battery has to meet various criteria: It must be highly conductive for lithium ions and at the same time capable of being produced as cheaply as possible on an industrial scale.
From lumps to ultra-thin layers
The ceramic compound LI7La3Zr2O12 (or LLZO for short) exhibits the appropriate properties and was the focus of a research project by Jordi Sastre, a PhD student at Empa. This ceramic has so far been produced for research purposes in the form of so-called pellets, the size of which is limited to a few centimeters in diameter. For use in batteries, these pellets first have to be elaborately polished – a time-consuming process, which is associated with high material losses. This method is therefore unsuitable for industrial production.
An ultra-thin LLZO layer would just be the solution; it would also have the advantage to allow lithium ions to flow through the electrolyte more quickly – thus increasing the battery’s performance. Using a method called magnetron sputtering, Sastre has now succeeded in producing an ultra-thin film of LLZO ceramic. The thickness of this film is in the range of 500 nanometers. For comparison, the diameter of a human hair is in the range of 40,000 to 100,000 nanometers, i.e. it is about 100 times thicker than the ceramic layer.