36 September/October 2023 | E-Mobility Engineering towards the electrolyte-electrode interface as the implanted argon ions repel the small, mobile lithium ions. This bulk migration accounts for the errors seen in lithium concentration in monatomic argon depth profiles and the increase in lithium concentration at the interface with the electrode. XPS is also suited to providing information relating to the interfacial material properties that are critical to the performance of batteries. Information derived from the technique can give insights into chemical composition, elemental or chemical distribution of species, defect sites or functional groups. Recent development of accessories for the spectrometers allows these materials to be studied in situ and in operation characterisation of the layers, which is also key for improving the computation models used in digital twins. Spatially resolved surface analysis is easily achieved using XPS imaging, available as standard with a spectrometer. Images of surface chemistry with a spatial resolution of a few microns over several millimetres can be acquired. Battery production, development and recycling Combining XPS with XRF analysis helps to verify the type and behaviour of raw materials, and gives a detailed picture of metal contaminants. This combination can provide a complete picture of the type, size and distribution of metal contaminants that are so detrimental to lithium-ion battery performance. Automated analysis, including the ability to detect contaminants beneath the surface, provide the accuracy needed for quality control and the speed for production use. For battery cells that are made in-house or come from a third-party supplier, or components that have failed in testing, the analysis shows the size, type and distribution of metal contaminants that could cause an internal short. Thermal analysis will show how novel materials behave at elevated temperatures, showing the distribution of particles within the battery before and after use, while handheld XRF can identify these elements in end-of-life batteries. A particle contaminant analyser with two X-ray sources is designed to help battery manufacturers improve the safety, performance and yield of the product. The analyser is engineered to rapidly detect and identify the unwanted metal particles within the battery that can cause sudden catastrophic failure of the batteries, often accompanied by fire or explosion. Metal contaminants can be introduced into the battery from the raw materials or the actual processing, as in metal particles from machinery. XPS is versatile enough to check for these in many stages during production, including as a final check before shipping the materials. X-ray transmission imaging can find metal particles in the material and show the size and shape, while XRF can determine which metal elements are present in the contaminated sites. Many of the components used in production, including carbon-based powders used in anodes for enhancing conductivity, cathode materials, the cell separator and the outer casing of the cell can be tested in the analyser. Solid components can be laid flat on the measurement platform, called a stage, while powders and slurries can be spread out in a transparent plastic container. The analyser is capable of detecting and analysing metal particles down to 20 µm in size, and rapid measurement allows large cathode plates for A4-size layers used in a production environment to be analysed. The X-ray transmission scan builds up an image of the material where the size and shape of any metal particles can be clearly seen. This gives important information on the size and density of the contaminants, and allows a part to be rejected if it is out of specification. XRF analysis of the contaminants reveals which elements are present, which again gives a complete picture of the contaminants, and which can be correlated with actual battery performance. Process control Having established that the raw materials are within specification regarding metal particle contamination, the next possible route for contaminants is from the Focus | Battery surface analysis An XPS system from Kratos Analytic in use for measuring battery materials (Courtesy of University of Nottingham)
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