Focus | Battery inspection 68 systems that use a variety of technologies. “In more mature manufacturing processes, there is greater understanding of failure modes and more consensus on tolerances and inspection approaches. With EV battery inspection, many manufacturers are still learning about what constitutes a relevant defect,” he says. “The exciting thing is that we get to help the battery industry develop that understanding to push the limits as the technology expands and grows.” This company’s inspection technologies include optical microscopy, X-ray microscopy, digital radiography, CF, traditional coordinate measuring machines (CMM), optical scanning, and structured light measurement. Staged inspections Different stages of battery manufacture require different inspection technologies. One of the earliest stages is electrode production, which involves the application of active anode and cathode compounds and binding agents in slurry form to sheets of substrates fed from a roll. These are then dried, compressed (“calendared”) and cut to size ready for assembly into cells, and this stage is well suited to inspection with specialised camera systems. While this can be done with area scanning cameras that capture discrete frames, these frames then have to be electronically stitched together before processing, which is not a natural fit for a continuous roll-to-roll process such as electrode production, notes our camera-based inspection expert. Wide, high-speed linescan cameras provide a better solution, he says, running at rates of around 100 kHz to expose 100,000 lines per second. This company uses time delay integration (TDI) technology in its linescan cameras that feature multiple rows of sensors covering every part of the surface being inspected. The TDI technology then combines all the exposures for each line – there can be 100 of them – to maximise the signal-tonoise ratio in the final image, he explains. TDI is particularly helpful in what he terms “light-starved” situations often encountered when inspecting dark materials or those that should not be exposed to high intensity lights for various reasons. “Using TDI means you can collect more photons but you don’t need to shine a bright light,” he adds. The TDI camera is an enabler for high speed imaging to meet the demanding requirement of high throughput production lines, he emphasises. Later in the manufacturing process, X-ray and CT allow thorough examination without compromising the integrity of the components being inspected, which is crucial to quality control. The latest systems also provide very highresolution images, ensuring precise and detailed visualisation of internal structures. This contributes to accurate defect identification and analysis. The latest systems also feature increasingly accurate AI-based automatic defect recognition capabilities. Combining processes Combining different inspection technologies can be particularly useful. “Each inspection technology has inherent benefits and limitations. Batteries are notoriously difficult to tear down, and the process of doing so can destroy much of the pertinent information,” our multi-technology inspection system expert says. He emphasises that X-rays can inspect internal features of complex parts across multiple scale lengths from centimetres to sub-millimetre volumes and capture relevant structural details with spatial resolutions ranging from microns to nanometres. This range of scales encompasses battery packs and cell-level analysis and material microstructure-level analysis. For example, it is possible to identify regions of interest using X-ray or optical microscopy scanning and then relocate that region of interest in a focused ion beam scanning electron microscope (FIB-SEM) for further high-resolution imaging and chemical analysis. The highresolution imaging capabilities of FIBSEM allow for an in-depth examination of the microstructure and composition of materials, offering a more granular understanding of the root causes of defects. However, FIB-SEM isn’t a nondestructive process because it requires extraction and preparation of small samples that must then be placed in a vacuum chamber. Described as a disruptive technology, 3D inline CT is designed to provide a more comprehensive and detailed inspection of batteries during the manufacturing process. This while operating at speeds high enough to keep up with modern battery production lines and minimising the likelihood of faulty batteries passing through the manufacturing process undetected. “By providing detailed insights into the internal structure and components of batteries, we enhance the overall safety standards, identifying potential issues before they can compromise the integrity of the product,” the X-ray and CT company’s expert says. The company’s new 3D inline CT technology, the expert says, can replace January/February 2024 | E-Mobility Engineering 3D X-ray nanotomography and digital material simulation map diffusion in an NMC li-ion cathode. The imagery came from a ZEISS Xradia 810 Ultra nanoscale X-ray microscope, and the data analysed with Math2Market’s GeoDict software (Image courtesy of ZEISS)
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