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Award-winning researcher sheds light on Li-ion batteries


Michael Metzger, researcher at the Technical University of Munich (TUM) has won the Evonik Research Prize for the development of a battery test cell that can investigate anionic and cationic reactions separately.

“Manufacturers of rechargeable batteries are building on the proven lithium-ion technology, which has been deployed in mobile devices like laptops and cell phones for many years,” he said.

“However, the challenge of adapting this technology to the demands of electromobility and stationary electric power storage is not trivial.”

According to Metzger, standard rechargeable batteries are not the best suited for high performance.

“To raise the energy density, you need to increase the voltage or the capacity, and that is where traditional electrode materials and electrolytic fluids reach their limits.”

This “battery doping” has side-effects; changes in the chemical composition of the electrodes and electrolytes can cause battery performance to drop after only a few charging cycles, or the formation of gases at the electrodes that cause the batteries to expand.

“The future of lithium-ion batteries hinges on getting a grip on these undesirable reactions,” said Metzger.

The researcher has already fulfilled one prerequisite to this end: The chemical processes that transpire during charging and discharging can be investigated in detail using the new battery test cell he developed with his team.

“Normally electrolytic fluids and electrodes – the positive cathode and negative anode – are in a permanent electrochemical exchange,” he said.

“Thus far it has not been possible to investigate the reactions at the anode and cathode independently of each other. We are the first to manage this successfully.”

The team’s battery test cell, which, like every lithium-ion battery, comprises an anode, a cathode and electrolytes is not completely sealed, but rather is fitted with a fine capillary. This allows gases that are released during charging and discharging to be sampled and investigated using a mass spectrometer.

To study the processes at anodes and cathodes independently of each other, the engineers also modified the membrane – a thin glass ceramic platelet coated with aluminium and synthetics – to make it permeable not only by lithium ions, but also by all other components of the electrolytic fluid.

  • Using their test cell, the researchers were, for the first time, able to explain precisely what transpires inside a high-voltage battery. The results demonstrate that the stability of electrodes and electrolytes depends on several factors, for example, charging voltage, operating temperature and even the tiniest chemical impurities: The higher the applied voltage and temperature, the faster the electrolytic fluid decomposes. The gases released in the process, mainly carbon monoxide and carbon dioxide, can cause the battery enclosure to ballon.
  • Even the smallest traces of water that intrude into the cell release hydrogen at the anode and acts as an oxidising agent on the carbon in the cathode. This impairs the conductivity of the electrode.
  • The chemical reactions that take place at the anode and cathode lead to interactions. This crosstalk, which has hardly been investigated to date, reduces the overall cell performance.

“For industrial end-users, the new measurement methodology is extremely interesting,” said Professor Hubert Gasteiger, chair of MUT’s department of technical electrochemistry.

“In our investigations, we were able to show that the development of gases in batteries can be reduced by adding the right admixtures to the electrolytic fluid or by inhibiting crosstalk between the electrodes.”

One research result, in particular, will have a direct consequence in practice: The higher the desired voltage, the less residual moisture the materials may contain. Manufacturers could extend the lifetime of future cells by replacing the electrolyte ethylene carbonate with more stable solution components. A small amount of ethylene carbonate is still required in current systems however, to pacify the anode.


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