38 September/October 2023 | E-Mobility Engineering production process itself. One way that can happen is from dust produced by production machinery. The contaminant analyser can scan the materials for levels of metal particles typically present in the dust. As well as identifying a source of contamination in the battery cell, this technique is useful for checking for potential problems in the machinery itself; a change in the amount or type of dust emitted could mean that a service is due or a part in the equipment needs replacing. Failure analysis This technique can also be used to determine the root cause of battery failure during the final testing phase of manufacturing. The surface analysis can determine whether any metal particles are present on the cell separator or electrodes that could have caused a short-circuit within the cell. XRF compositional analysis will determine exactly which metals are present, in what size and quantity, to identify where the contaminants came from. This allows the correlation of specific patterns of contamination with performance, so that only the parts where the contamination compromises the performance are rejected. Analysis of dry electrode layer manufacture Research in the US has shown there are significant benefits to a dry battery manufacturing process, but such a process needs a detailed analysis of the resulting material surfaces. The dry anode process eliminates the solvents used in manufacturing to reduce the inactive elements and so increase energy density. Dry processing is a relatively new alternative that saves factory floor space as well as time, energy, waste disposal and start-up expenses, yet until now, researchers have had only a limited understanding of how and why it works. The process involves mixing dry powders with a binder, then compacting the material to improve contact between the particles. The electrochemical performance of the material in different conditions is measured over various time frames to determine how the dry-processed electrodes degrade. These measurements show that the dry anode structure allows lithium ions to take a more direct path between the anode and cathode, allowing the electrodes to be thicker for higher energy loading while reducing inactive ingredients that merely increase size and weight. The electrode also bends and flexes well, demonstrating excellent mechanical strength and the winding capability needed for mass production of batteries with fewer cracks than other techniques. The next step in the US research is to stabilise the material that attaches the anode components to a thin metal current collector. A main goal for the project is to develop or identify a better binder for the dry process, because the present one is not very stable for the anode environment. The researchers are also working on reducing the amount of carbon black used in the binder material. Another technique for analysing the surface of battery materials is secondary ion mass spectrometry added to existing focused ion beam systems. This provides measurement for light elements such as lithium with sub-ppm sensitivity. Laser diffraction Rechargeable lithium-ion batteries use an intercalated lithium compound as the electrode material. A lithium titanate battery is a modified lithium-ion battery that uses lithium titanate nanocrystals on the surface on the anode. These have a range of materials, from lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4) and lithium iron phosphate (LiFePO4) for the cathode, to carbon, lithium and lithium titanate (Li2TiO3) for the anode. Laser diffraction can be used to determine the particle size distribution (PSD) of the battery materials used in r&d as well as quality control for product acceptance, as a PSD specification typically exists for a material used in production. Particle size influences capacity and coulomb efficiency, and reducing the PSD will increase the specific surface area, changing important battery characteristics as it also changes the size of the voids between electrode particles, reducing battery capacity. This system combines XPS with XRF for surface analysis (Courtesy of Hitachi Hightech)
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