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Detection of Very Low-Level Contaminants in a Battery Cathode

Contamination analysis and control of battery anode and cathode materials and other component surfaces and interfaces are essential in order to understand and improve battery cell properties. High-sensitivity energy dispersive X-ray spectroscopy (EDS) detectors can be used in addition to conventional bulk trace element analysis methods (XRF). EDS detectors do not only detect the presence of a certain contaminant in a bulk sample, but via EDS mapping they can also reveal their distribution. This additional information about the location of different contaminants can help to determine their origin.

The EDS analysis of samples with a micron-sized grain structure without preceding sample preparation is always challenging. The elemental maps are affected by shadowing when they are analyzed with EDS detectors of conventional geometry. Annular EDS detectors such as the Bruker XFlash® FlatQUAD deliver shadow-free elemental maps thanks to the significantly higher take off angle. Furthermore, due to the higher detectable signal rate (input count rate), the Bruker XFlash® FlatQUAD detector features a fundamentally higher sensitivity, which enables the identification and localization of very low-quantity contaminants in a short amount of time.

This webnote demonstrates one example for the identification and localization of a certain element species (vanadium) of contamination found in a pristine cathode sample. The cathode material FeLiPO4 (deposited on aluminum foil) was investigated in top view (no sample preparation). Elemental maps were acquired using Bruker XFlash® FlatQUAD annular detector and the contaminants were identified using the Maximum Pixel Spectrum function. 

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Figure 1a. Elemental map of vanadium with (in the front) and without SE image overlay (in the background) of a LiPO4 cathode sample acquired with Bruker XFlash® FlatQUAD EDS detector. Vanadium was found in a single sub-micron sized particle and its presence was proven with the spectrum extracted from the single particle area. The concentration of V is on the 10 ppm level in the mapped area.
Figure 1b. The X-ray signal of a single sub-micron particle is buried in the sum signal of the whole map area (blue). The maximum pixel spectrum function (red) identifies the buried V-peak. The measurement time was only 3 minutes.