EDS Analyses of Coated Li-ion Battery Cathode Particle

Nickel-Cobalt-Manganese (NCM) particles are used as cathode materials for Li-ion batteries. In this application example, we use NCM particles coated with titanium (Ti) by Atomic Layer Deposition (ALD). The homogeneity of the coating is important when studying the capacity retention. While it is difficult to distinguish the Ti layer from the base material with SEM or TEM imaging, the coating distribution can be determined by EDS elemental analysis.

To access the surface of single micrometer-sized particles, a specimen was prepared in cross-section by FIB-SEM. We present a comparative study of the same sample area analyzed by STEM EDS in a transmission electron microscope and by T-SEM EDS in a scanning electron microscope. Measurements were conducted using XFlash® 760 conventional X-ray EDS detector and in case of SEM, additionally, an X-ray EDS detector with annular detection geometry, the so-called XFlash® FlatQUAD.

The 20-30 nm thick Ti-coating can be identified, and its homogeneity can be examined not only in TEM, but also using a conventional setup with an XFlash® 760 detector in SEM. In the same measurement time, elemental mapping with the annular XFlash® FlatQUAD detector achieves much higher data quality compared to conventional SEM EDS and could yield the same data quality 15 times faster thanks to the higher X-ray collection solid angle in annular geometry. 

Comparison of the same Ti-coated NCM Li-ion battery particle in cross section, measured with: a) HAADF image and S(T)EM EDS b) conventional SEM EDS c) annular SEM EDS (XFlash FlatQUAD). Image and sample courtesy of Michael Malaki, Shamail Ahmed; Material Science center, Faculty of physics, Philipps University Marburg