Two crucial points ensure that solid-state batteries without the otherwise typical liquid electrolyte remain the focus of research. Such a battery cannot leak and is considered to be much more resistant to fire than normal lithium-ion batteries. In addition, the energy density is on a par with the best current models and could increase further.

If only there wasn't the problem that one of the most promising electrolytes with its very high ionic conductivity has a major problem. Its remarkable conductivity makes it highly reactive, so that a protective layer forms rapidly on contact with air, similar to that of aluminum or copper.

As a result, the performance of the battery decreases very quickly, meaning that the service life of solid-state batteries cannot keep up with current batteries in electric cars and certainly not with the best models, which achieve well over 10,000 charges.

Instead of developing ever better protection against these chemical processes, Pohang University in South Korea has taken a different approach. A hydrophobic additive was added to the solid electrolyte made of lithium, lanthanum, zirconium and oxygen (LLZO for short). This in turn consists of lithium, aluminum and oxygen

It therefore shares a whole range of properties with the actual electrolyte, which means that the outstanding values of the battery do not deteriorate. At the same time, unnecessary components of the system can be omitted because humidity and water cannot harm the battery.

The result is a battery barely 10 micrometers in size, thinner than a human hair. In addition, the design is extremely robust against external influences and the energy density is an impressive 500 watt hours per kilogram.

It will be interesting to see what ultra-thin batteries can be used for. Or it may even be possible to increase the energy density of the system even further. Then the batteries can be thicker and used for mobile applications.