Elemental Mapping of Contaminants in Battery Electrodes

The optimization of battery cell chemistries and their manufacturing processes is critical in achieving a clean energy economy. The properties of a battery cell properties are related to electrochemical reactions inside the cell and any structural features that have formed during the manufacturing or cycling processes. Elemental mapping via energy dispersive X-ray spectroscopy (EDS) is part of a multiscale, multimodal analytical approach that includes analysis of the anode, cathode, electrolyte, and their respective interfaces.

EDS can be used in the optimization and quality control of anode and cathode materials as it allows users to investigate the main cell components and to identify and localize contaminants on the micrometer scale. Here we present the use of two types of Bruker EDS detectors as analytical tools for the elemental mapping of a carbon anode and a LiPO₄ cathode material sample. A conventional EDS detector, XFlash^®760, and our unique, annular XFlash^® FlatQUAD detector, were used.

A direct comparison of the EDS maps acquired on the same sample areas with a conventional and an annular detector geometry proves the unmatched versatility of the annular XFlash^® FlatQUAD detector (figure 1).

Figure 1a. Left: EDS elemental map with SE image overlay of a carbon anode sample acquired with Bruker XFlash^® 760 EDS detector in cross section geometry. Note that the non-colored areas show no elemental information as these areas are not accessible with a conventional detector geometry since they are shadowed by the high topography of the unprepared sample.

Figure 1b. Right: EDS elemental map with SE image overlay of a carbon anode sample acquired with Bruker XFlash^® FlatQUAD EDS detector in cross section geometry. Note that element distribution information of the whole sample area can be accessed using annular EDS geometry.

EDS analysis of samples with a micron-sized grain structure without any sample preparation (mechanical or FIB polishing) is always affected by shadowing if carried out using EDS detectors with a conventional geometry. Annular EDS detectors such as Bruker's XFlash^® FlatQUAD overcome this issue. The significantly higher take off angle enables XFlash^® FlatQUAD to see in between the grains and access the intergranular surfaces despite the rough topography.

This example (figure 2) shows the element distribution of the main component (carbon) and additional contaminants on a pristine carbon electrode sample. The carbon anode layer was deposited on a copper foil and the sample was investigated in cross section (prepared via simple mechanical cutting – without any meticulous sample preparation).

Comparison measurements between Bruker XFlash^® 760 EDS detector, which has a conventional EDS geometry, and the Bruker XFlash^®FlatQUAD annular detector (figure 1) show that the full sample area cannot be accessed when using conventional EDS detection geometry. This is because the high sample topography results in shadowing of the X-ray signal in deeper sample regions.

Elemental maps acquired with the Bruker XFlash^®FlatQUAD can access and visualize the distribution of the main component (carbon) and the identified contaminants on the whole mapped sample surface.

Figure 2: Combined EDS map of a FeLiPO4 cathode layer (deposited on Al foil) with SE image overlay acquired with Bruker XFlash^® FlatQUAD EDS detector in cross section geometry.

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