TUM researcher Fabian Apfelbeck is working with a measuring device that can be used to examine the charging and discharging cycles of button cells. (Credit: Vera Hiendl, from 'e-conversion')
Dendrites are considered the most dangerous destroyers of lithium batteries — tiny metal structures that can cause short circuits. In the worst case, they can cause batteries to burn or explode. An investigation at DESY´s X-ray light source PETRA III has discovered that such structures can form not only at the electrodes but also in polymer-based electrolytes. This new finding by a research team from the Technical University of Munich (TUM) in Germany is crucial for the stability of future solid-state batteries.
Lithium-metal batteries are among the most promising technologies for energy storage. They offer significantly more energy in less space — and at a lower weight. However, one phenomenon slows down their development: tiny, needle-like metal structures called dendrites, made of lithium. They can grow uncontrollably inside the battery and cause devastating short circuits. Until now, solid electrolytes, including polymer-based electrolytes, have been considered a way to suppress this growth.
“Electrolytes are responsible for transporting lithium ions back and forth between the two electrodes inside a battery — making the flow of current possible in the first place,” explains Fabian Apfelbeck, first author of the study published in the journal Nature Communications. The physicist is pursuing his doctorate in the research group of Peter Müller-Buschbaum at the Chair of Functional Material at TUM and is funded by the Excellence Cluster 'e-conversion'.
Polymer-based electrolytes offer greater stability and safety than liquid electrolytes because they cannot leak or ignite. They also reliably separate the electrodes from each other and thus prevent short circuits. “However, our measurements show that dendrite growth can also occur directly inside the polymer electrolyte — right in the material that is actually supposed to protect against dendrites,” says Apfelbeck.
Using a nanofocus to look inside the battery
The findings, therefore, challenge a central assumption in battery research. Müller-Buschbaum explains: “Until now, it was assumed that dendrite growth occurs only at the interface between electrode and electrolyte. The fact that it also appears far away from that interface surprised us. This new knowledge helps us develop — and further improve — materials in which such internal crystallisation processes do not occur in the first place — enabling more efficient, safer, and longer-lasting energy storage.”
The researchers used a particularly precise method for their investigations: so-called nanofocus wide-angle X-ray scattering experiments, carried out at the PETRA III beamline P03. Using an X-ray beam with a diameter of just 350 nanometers, they could visualise the microscopic changes inside a polymer-based electrolyte during battery operation for the first time. To do so, they used a specially developed miniature cell that allows the battery to be observed under real operating conditions.
(Partly from DESY News)
Reference:
F. A. C. Apfelbeck, G. E. Wittmann, M. P. Le Dû, L. Cheng, Y. Liang, Y. Yan, A. Davydok, C. Krywka, P. Müller-Buschbaum, Local crystallization inside the polymer electrolyte for lithium metal batteries observed by operando nanofocus WAXS, Nature Communications (2025). DOI: 10.1038/s41467-025-64736-w
