Researchers clear away obstacle for lithium-air batteries

Researchers clear away obstacle for lithium-air batteries

Technology News |
By Jean-Pierre Joosting

In the lithium-air battery, the energy density is, at least in theory, ten times higher compared to conventional lithium-ion batteries. In addition, in this technology porous carbon particles replace the heavyweight electrodes made by the oxides of transition metals and thus enables the design of lightweight batteries. While this looks like a perfect combination, today’s lithium-air prototype batteries exhibit a massive drawback: They tend to drastically lose their performance already after a few charging cycles, and the electrodes disintegrate. Scientists from the Munich Technical University (TUM) and the Jülich Research Center now have found the reason for this behavior: During the charging process, highly reactive singlet oxygen is generated. This oxygen corrodes surrounding materials within the fraction of seconds, explains doctoral candidate Johannes Wandt from TUM.

There are two reasons why the scientific community did not find out earlier the reason for the short live cycle of lithium air batteries: One is the rather complex experimental setup. And the other one is that there has been a miscalculation in the scientific literature that kept scientists from searching in the right place, Wandt assumes.

To examine the charging process more exactly, the TUM researchers built a specific lithium-air battery. The current collectors are very thin and shaped as a helix; a glass case enables the scientists to observe the process visually. In addition, the glass casing makes sure that RF radiation and magnetic fields relevant are not shielded off, but can be measured as well. In addition, the scientist colleagues from Jülich applied a specific measurement instrument for so-called Electron Pragmatic Resonance Spectroscopy (EPR) that enabled them to prove the generation of singlet oxygen when the battery was charged.

The problem is now identified, but is there a solution in sight? Not quite. In the next step, the researchers plan to find ways to prevent the generation of singlet oxygen. This work still falls into the area of fundamental research, but “it could create the prerequisite for the design of novel, long-lasting lithium-air batteries”, Wandt hopes.

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