Examining metal anode operation in batteries
Researchers in Germany have developed a technique to examine the layers in a metal anode in a battery during operation.
The team of scientists from the Münster Electrochemical Energy Technology battery research centre (MEET) at the University of Munster and the University of Oldenburg’s Chemistry Department developed a new measuring principle to obtain local, high-resolution information about the surface of metallic lithium electrodes during battery operation. “Over time, chemical processes on the electrode’s surface can have a major impact on the durability and performance of a battery,” said Prof. Dr. Gunther Wittstock of Oldenburg.
The researchers used scanning electrochemical microscopy (SECM) for their metal anode analysis. This procedure involves scanning a measuring probe across the surface of a sample to collect chemical information at intervals of a just a few micrometres. Special software then translates the measured data into a coloured image. “By repeating this process several times we can track changes on the sample’s surface like in a flipbook,” said Wittstock.
The new technique could accelerate the search for suitable materials for innovative batteries, with the ultimate objective of developing eco-friendlier energy storage devices that are more durable and have a higher power density.
In a lithium battery, ultra-thin layers form on the surface of the anode which protect both the electrode and the battery fluid from decomposition. Until now, however, it has been almost impossible to directly observe the changes that take place in these complex micron-think layers during charging and discharging cycles.The team has
Bastian Krueger, a PhD student of Wittstock’s Physical Chemistry research group, developed a special measuring cell in which experimental conditions – such as current intensity – essentially corresponded to those in a real battery. The chemist tested various cell assemblies which he produced using 3D printers and CNC micro-milling machines. Luis Balboa, another PhD student of the same group, carried out computer simulations to optimise the cell geometry that recreate realistic experimental conditions. The team from Munster contributed reference samples.
With this setup, the scientists were able to observe the processes on the lithium anode with an unprecedented degree of accuracy. They observed how, at high charging speeds, lithium from the battery fluid was deposited on the metal anode. These locally reinforced deposits can develop into so-called dendrites – branching extensions of lithium on the electrode. Such formations limit the durability of batteries and in extreme cases can even cause their destruction.
“The breakthrough in our study consists in the fact that for the first time ever we were able to carry out such processes at realistic current densities directly within the measuring apparatus and visually monitor their effects,” said Wittstock. The key is that the technique could also be used on other types of electrodes, he added, explaining that the long-term objective was to study how different pre-treatment steps influence the formation of a protective boundary layer on electrodes.
The work is part of a project called “Alternative Materials and Components for Lithium-Oxygen Batteries” (AMaLiS) which receives funding from the German Federal Ministry of Education and Research (BMBF) until the end of 2020.
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