A part of our experiments are carried out at international synchrotron facilities. A synchrotron is a particle accelerator, which generates very intense electromagnetic radiation (e.g. X-rays) with high energy and high brilliance. This powerful radiation allows us to do unique experiments such as looking at the atoms inside a battery while it is running. This allows us to understand the fundamental processes that occurs at the atomic level during charge and discharge. The reversibility and stability of these structural changes has a significant influence on the capacity, lifetime and safety of the battery.
A powerful method of studying material structures at the atomic scale is X-ray diffraction. Here the electrode material is irradiated by a focused X-ray beam, which is reflected (diffracted) in specific angles by the electrode. The reflection angles depend on the distances between the atoms in the material, while the intensity of the reflected beam depends on which type of atoms the material is made from. Hence, each material has a unique ”X-ray fingerprint”. Even very small changes in the atomic structure of the material are observed as changes in the reflected X-ray beam.
Recently methodologies to collect X-ray diffraction data from a battery while it is in operation have been developed. For these experiments specially designed battery test cells are utilized. The test cells are designed to allow the X-ray beam to penetrate through the entire battery. To achieve this, it is necessary to utilize X-rays with both a very high intensity and energy. Therefore, these experiments are therefore carried out at international synchrotron facilities, which can deliver the required radiation. With this equipment, we can take a high-resolution “X-ray picture” of the battery in 10-30 seconds. If such pictures are recorded continuously while the battery is running an “X-ray movie” is obtained, which can be transformed into a movie on how the atomic structure of the electrodes change during battery charge and discharge.
Currently, we utilize synchrotrons in Germany (PETRAIII) and USA (APS). Associate Professor Dorthe B. Ravnsbæk is also part of the consortium for the construction of the Danish beamline DANMAX at the new synchrotron MAXIV in Lund, Sweden.