E-Mobility Engineering 017 l ECE Doosan electric excavators dossier l In Conversation: Matt Faulks l Battery testing focus l Battery Show North America 2022 report l Ariel Hipercar digest l Cathode materials insight l Thermal management focus

X-ray photoelectron spectroscopy is another way to evaluate the anode material. Here, X-ray beams are shot into an anode, ejecting electrons from it with a certain energy. This showed that the niobium atoms gain multiple electrons as the cell is charged, suggesting that the anode has a high storage capacity. Yet another technique, X-ray absorption spectroscopy, is used to hit the anode material with intense synchrotron X-ray beams and measure the transmission and absorption of the X-rays in the material. This provided an overall picture of the state of the electrons across the entire anode. There are also several key X-ray technologies for identifying contaminants in battery materials. 75% of the cost of a battery cell is in the materials, so identifying contaminants early in the process can help reduce the scrap rate and lower the cost of a cell. It can also help with recycling. X-ray transmission takes an image as a line through a material to detect the embedded contaminants, which can be as small as 20 microns. A scan using a 17.5 kV X-ray source at 35 mA of a 250 x 200 mm sample of material can take 7 to 10 minutes. X-ray fluorescence operates at 45 kV up to 1 mA is then used to identify any contaminants in a material. A 20 micron contaminant can take 60 to 90 seconds to analyse, and the overall scanning time depends on the number of contaminant particles in the sample. The key is the X-ray optics that focus the full energy of the beam into the contaminant particle. The system, called polycapillary optics, uses an array of small hollow curved and tapered glass tubes through which the X-rays are guided by multiple internal reflections. The system includes a silicon drift detector to pick up the fluorescence from the contaminating particle’s X-rays to determine what it is made of. The process can be automated to examine contaminants above only a specified size, as well as specifying the number of particles to be examined, which speed up the process. The data from the contaminants can also be stored for analysis by ML algorithms to further speed up the testing process. These automated processes – or ‘recipes’ – can be set for different materials, optimising the testing speed depending on the type of material such carbon black, separator, anode and cathode electrodes and the risk of contaminants being present. X-ray for cells in operation X-ray diagnostics are also used to assess the operation of a battery cell rather than the materials before they are assembled. X-rays can probe changes as they occur in real time without significantly interfering with the cell. This requires special in- situ environments for imaging during the mechanical, electrochemical or thermal changes within the material of interest. X-ray computed tomography has been used to build a comprehensive electrode microstructure library images based on the interaction of the electrons with the sample. As the electron beam is focused on a small part of the sample, the technique provides detailed information about that particular area. A device known as the Advanced Photon Source confirmed the structural change with another technique called synchrotron X-ray diffraction. The non- invasive test procedure involves hitting the sample with high-energy X-ray beams, which are scattered by the electrons of the atoms in the material. A detector measures this scattering to characterise the material’s structure. X-ray diffraction is effective for providing information about overall structural changes across an entire material sample. That can be helpful when studying battery electrode materials, because their structures tend to vary from one area to another. Hitting the anode of a cell with X-ray beams at different angles confirms that it was uniformly crystalline along the surface and in the interior. Using X-ray computed tomography to diagnose lithium-ion batteries (Courtesy of Dennis Schroeder, NREL) January/February 2023 | E-Mobility Engineering 35 Focus | Battery testing