X-ray Photodecomposition of Bis(trifluoromethanesulfonyl)imide, Bis(fluorosulfonyl)imide, and Hexafluorophosphate

X-ray photoelectron spectroscopy is one of the workhorses in today's battery analysis and research. The potential of X-ray radiation damage and degradation during measurements with regularly used salts and organic compounds are often overlooked. In this study, we show that, under common analysis conditions, the exiting X-ray radiation (1468.6 eV) during the XPS analysis does have significant effect on some Mg and Li salts based on TFSI, FSI, and PF₆ anions. In all cases, we show that the salts undergo significant photodegradation during the XPS measurements. With XPS, the photodegradation is detected as the solid degradation products remaining on the sample holder, and they are clearly identified by formation of new peaks at lower binding energies for the relevant elements. We were also able to show that in some cases, as expected, some gaseous byproducts evolve during the photodegradation process.