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Technische Universität München

Neutrons show how lithium-ion batteries can be filled faster


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Filling lithium-ion cells faster

Neutrons pave the way to accelerated production of lithium-ion cells

Developers from Bosch and scientists at the Technical University of Munich (TUM) are using neutrons to analyze the filling of lithium ion batteries for hybrid cars with electrolytes. Their experiments show that electrodes are wetted twice as fast in a vacuum as under normal pressure.

One of the most critical and time-consuming processes in battery production is the filling of lithium cells with electrolyte fluid following the placement the of electrodes in a battery cell. While the actual filling process takes only a few seconds, battery manufacturers often wait several hours to ensure the liquid is fully absorbed into the pores of the electrode stack.

The fact that neutrons are hardly absorbed by the metal battery housing makes them ideal for analyzing batteries. That is why Bosch employees, in collaboration with scientists from the TU Munich and the University of Erlangen-Nuremberg, investigated the filling process at the neutron imaging and tomography facility ANTARES of the research neutron source FRM II.

Faster in a vacuum

Manufacturers of lithium cells often fill the empty cells in a vacuum. The process is monitored indirectly using resistance measurements. "To make sure that all the pores of the electrodes are filled with the electrolyte, manufacturers build in large safety margins," says Bosch developer Dr. Wolfgang Weydanz. "That costs time and money."

In the light of the neutrons, the scientists recognized that in a vacuum the electrodes were wetted completely in just over 50 minutes. Under normal pressure, this takes around 100 minutes. The liquid spreads evenly in the battery cell from all four sides, from the outside in.

In addition, the electrodes absorb ten percent less electrolyte under normal pressure. The culprit is gases that hinder the wetting process, as the scientists were able to demonstrate for the first time using the neutrons.


Visualization of electrolyte filling process and influence of vacuum during filling for hard case prismatic lithium ion cells by neutron imaging to optimize the production process

W.J. Weydanz, H. Reisenweber, A. Gottschalk, M. Schulz, T. Knoche, G. Reinhart, M. Masuch, J. Franke, R. Gilles

Journal of Power Sources, Volume 380, 15 March 2018, Pages 126-134, DOI: 10.1016/j.jpowsour.2018.01.081


High resolution images:

Video of the filling process:


Filling of a lithium-ion cell (left: normal pressure, right: vacuum): The wetting of the electrode (dark area) proceeds evenly from all sides. After approx. 50 min., the electrode filled under vacuum is completely wetted. (Image: Wolfgang Weydanz/Ralph Gilles / Bosch/TUM)


Dr. Ralph Gilles

Technical University Munich

Research-Neutronsource Heinz Maier-Leibnitz (FRM II)

Lichtenbergstr. 1, 85748 Garching, Germany

Phone: +49 89 289 14665 - e-mail:

The Technical University of Munich (TUM) is one of Europe's leading research
universities, with around 550 professors, 41,000 students, and 10,000 academic
and non-academic staff. Its focus areas are the engineering sciences, natural
sciences, life sciences and medicine, combined with economic and social
sciences. TUM acts as an entrepreneurial university that promotes talents and
creates value for society. In that it profits from having strong partners in
science and industry. It is represented worldwide with the TUM Asia campus in
Singapore as well as offices in Beijing, Brussels, Cairo, Mumbai, San Francisco,
and São Paulo. Nobel Prize winners and inventors such as Rudolf Diesel, Carl von
Linde, and Rudolf Mößbauer have done research at TUM. In 2006 and 2012 it won
recognition as a German "Excellence University." In international 
rankings, TUM
regularly places among the best universities in Germany.
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