34 September/October 2023 | E-Mobility Engineering Nick Flaherty explains how techniques for analysing the surface of battery materials are leading to better cell designs Crystal clear Materials analysis is essential in developing new battery components and ensuring they meet high standards of quality. Thermal analysis meanwhile plays an important part in raw materials characterisation, especially for thermal runaway issues. Lithium-ion technology is still in development to increase performance in terms of energy density and longevity. Issues with safety that have caused fires and explosions in vehicle battery packs have not yet been completely resolved, so materials analysis is vital during the development, manufacturing and recycling processes. There are many different techniques for analysing the surface of materials. New techniques such as cryo-EM are showing the crystal structure of metals in batteries, and digital twin technology is enhancing that analysis. X-ray analysis is one technique for rapid battery quality control and failure analysis, while handheld X-ray fluorescence (XRF) excels at identifying key battery elements during the end-oflife recycling process. The energy storage capacity of lithium-ion cells fades over time owing to chemical and structural changes in their components, via different degradation mechanisms. Understanding and mitigating those degradation mechanisms are key to reducing capacity fade, thereby enabling improvements in the performance and lifetime of lithium-ion batteries. Surface analysis techniques are commonly used to characterise the chemistry and structure at reactive interfaces, where most changes are observed as batteries age. However, battery electrodes are complex systems containing unstable compounds, with large heterogeneities in the properties of their materials. Different degradation mechanisms can affect multiple material properties and occur simultaneously, so a range of complementary techniques must be used to obtain a complete picture of electrode degradation. The combination of these issues and the lack of standard measurement protocols and guidelines for data interpretation can lead to a lack of trust in the resulting data. This can present test engineers and materials researchers with a major challenge. Several surface analysis techniques are being used for lithium-ion battery degradation studies. Examples include focused ion beam scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and time-of-flight secondary ion mass spectrometry as well as laser diffraction for nanoparticles.
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