Air-sodium battery becomes durable and efficient

An electrode, which is basically just the surrounding air, promises extreme simplification in the construction of rechargeable batteries. However, humidity and, not least, oxygen are among the substances that subsequently attack the metal anode and cause a comparatively rapid loss of performance. Elaborate air filters would therefore be necessary to prevent this

The battery cell presented at Pohang University in South Korea is a completely different story. Here, the researchers were able to show that the chemical reactions with oxygen, CO2 and water actually increase the performance of the cell, which is not least due to a so-called sodium (Na) super ionic conductor (NASICON) that covers the anode.

It forms a solid electrolyte composed of sodium, silicon and zirconium, among other things. It also contains nickel, which is important for the reaction with carbonic acid. This is produced from water and CO2. Both substances are present in air and ensure the formation of an additional porous layer in which sodium ions also accumulate and increase the conductivity of the ions.

As a result, the cell presented here achieves practical voltages of almost 3 volts and can be recharged with just one volt more. This is particularly important in order to achieve high efficiency. If the voltage during charging and discharging is too far apart, considerably more current is required for charging than is available later.

However, there is still some way to go before this can be used in practice. In the published study, 100 charges were achieved - with a remaining power of 86 percent. For practical use, a tenfold increase would of course be desirable.

One feature of the promising battery should particularly please residents of temperate climates. The usual humidity of 70 percent there ensures maximum performance of the metal-air battery. The e-car can then travel a few miles further.