High-Resolution\nX‑ray Mapping of Fluorinated\nBinders in Lithium-Ion Battery Electrodes

This study looks\nat energy-dispersive X-ray spectroscopy\n(EDX)\nmaps of fluorine in NMC 622 cathodes and the efforts made to improve\nthe spatial resolution of fluorine mapping. The transition to electric\nvehicles demands faster and efficient production of next-generation\nlithium-ion batteries. To achieve this goal, the industry needs to\ntake advantage of state-of-the-art battery characterization techniques\nin the pursuit of gaining a greater understanding of electrode structure\nand production. The binder location within an electrode is critical\nto electrochemical performance and contains fluorine, yielding an\nopportunity to use it as a marker and a way to visualize binder distribution\nand therefore, better understand process-structure relations. However,\nfluorine is difficult to differentiate from cobalt and manganese in\nan EDX spectrum due to similar Kα energy. Fluorine also interacts\nwith the electron beam, potentially leading to poor spatial resolution.\nThis paper examines different EDX parameters and compares the spatial\nresolution of fluorine in the maps of lithium-ion cathode cross sections.\nAnalysis of the EDX maps showed that reducing the accelerating voltage\nfrom 20 to 5 kV improved the spatial resolution of fluorine 10-fold,\nfrom 2553 to 238 nm, supported by CASINO simulations. The EDX maps\nalso indicated that imaging for one long scan at a 2500 μs dwell\ntime produced a higher spatial resolution than imaging for 10 scans\nat 250 μs. Repeated line scans of the sample showed the extent\nof fluorine mobility; fluorine-rich zones emit less, while fluorine-free\nzones begin to emit more fluorine X-rays. This work shows that the\nspatial resolution of fluorine maps can be increased by imaging at\n5 kV and scanning for one pass at 2500 μs. This methodology\ncan be used to create more representative EDX maps of the binder in\nthe cathodes. Visual analysis or further processing with an image\nanalysis can reveal binder distributions and potential binder gradients.\nThis technique is useful in understanding how changes to electrode\nmanufacturing can change the electrode structure and binder distribution.