Using neutrons, a research team led by the Technical University of Munich has looked deep inside batteries as they were charged and discharged. The knowledge gained from the observations could help optimise charging processes.
What the internal structure of a battery looks like before and after charging is already known. Now, for the first time, a research team led by the Heinz Maier Leibnitz Centre at TU München also observed the lithium distribution of a battery during the complete charging and discharging process at the Stress-Spec materials research diffractometer. They checked the measurements on the high-resolution powder diffractometer Spodi.
During charging, the lithium ions migrate from the positively charged electrode to the negatively charged electrode, and in the opposite direction during discharging.
In the investigations that have now been carried out, the researchers were able to observe that the distribution of the lithium constantly changes during charging and discharging. »If the lithium is unevenly distributed, the exchange of lithium between the anode and cathode does not function one hundred percent in areas of the battery where there is too much or too little lithium. An even distribution, on the other hand, increases performance,« explains Dr. Anatoliy Senyshyn from the Heinz-Maier-Leibnitz Research Neutron Source (FRM II) at TU München (TUM).
The researchers succeeded in capturing the uneven distribution of lithium in a battery with very high resolution: In order to record the entire battery, they examined one tiny subvolume after the other and then combined these individual measurements into one large picture.
With the help of the German Electron Synchrotron Desy of the Helmholtz Association and the European Synchrotron Radiation Facility (ESRF), it was possible to select partial volumes with dimensions in the micrometre range. In this way, the researchers recognised that the lithium is not only unevenly distributed along the electrode layers, but also perpendicular to the layers.
The observed effects could help in the long term to further develop batteries, for example for electric cars, says Senyshyn: »Many properties of batteries can be influenced by the distribution of the lithium. If we have better control of these, we can significantly improve the performance of batteries in the future.«