Dislocations play a key role in battery failure

The cases of Lithium-ion batteries shorting and leading to catastrophic fire are becoming increasingly common due to their use in many appliances. The causes of these fires can be various. The presence of dendrites (‘branches’ in Latin), which are metal filaments that appear between the anode and cathode, has been pointed as the cause of failure in the past. 

Lithium dendrites form when extra lithium ions accumulate on the anode surface and cannot be absorbed into the anode in time. In batteries using liquid electrolyte, which are the majority, dendrites can shortcircuit and cause a fire due to the flammability of the liquid electrolyte.

Researchers around the world are now eyeing a replacement for the liquid electrolyte for a thinner and lighter layer of solid ceramic. This material makes the battery lighter, sturdier and less prone to the formation of dendrites.

A team led by NTNU (Norway) and the ESRF has now found some dislocations in solid electrolytes containing a dendrite, which has been electrochemically induced. The dendrites in the samples had appeared halfway between the anode and the cathode. The scientists used Dark Field X-ray Microscopy (DFXM) and found dislocations at the tip of the dendrites.

Chicken and egg dilemma

“This raised a question like the chicken and the egg dilemma: what came first, the dislocation or the dendrite?” explains Can Yildirim, scientist at the ESRF and ERC Starting Grant awardee.

The data of the experiment showed that dendrites growth increases the stress and this creates dislocations, which act as weak points that guide new different branches of dendrites. “If we can tune down the dislocation directions we can maybe tweak the dendrites propagation”, explains Daniel Rettenwander, professor at NTNU and corresponding author of the publication.

Most ceramics, due to their low dislocation density, do not allow for the visualization of dislocations using standard experimental methods. At the ESRF, thanks to the new Dark field X-ray Microscopy, a non-destructive diffraction technique, researchers acquired a high field of view in the order of hundreds of microns, with the spatial resolution of nanometers, of the samples. The technique provided a 3D vision of the plane, where they could track how dislocations are positioned in the 3D structure.

How did they know that the dislocations were not just random cracks? Since 2016, we have been working on dislocations in metals mainly, in collaboration with the Danish Technical University (DTU) and Stanford University, and we’ve reached a level where we can identify the footprints of dislocations, also in other materials, such as ceramics.

Can Yildirim in the new ID03 beamline Experimental Hutch. The new beamline, together with the EBS, will provide more than a 10-fold increase in resolution in future experiments. Credits: S. Candé.

This work is also a testament to the collaboration between scientists at the ESRF. “Before this experiment, I didn’t really know much about batteries, as it is not my field”, explains Yildirim. “But at the ESRF we are lucky to have experts in many fields, and ID31 scientists Valentin Vinci and Marta Mirolo brought to me valuable insights into the paper with their expertise in batteries”.

The next step for the scientists is to visualize the dendrites during operation. This kind of experiment requires a higher photon flux, but thanks to the new EBS capabilities, together with the new optics, detectors and cameras, which provide more than a 10-fold increase in resolution on the new ID03 beamline, Yildirim is confident of the success of the experiment.

Reference:

Yildirim, C., et al. Nat Commun 15, 8207 (2024). https://doi.org/10.1038/s41467-024-52412-4

Text by Montserrat Capellas Espuny

Top image: A 3D orientation map of the Dark Field X-ray Microscopy images acquired during the experiment. Credits: Can Yildirim.