PNNL

Abstract

X-ray photoelectron spectroscopy (XPS) has become a highly important tool for the analysis of battery materials and components. However, both antidotal and detailed analysis of parts of the literature indicate that many reports of XPS on battery electrodes have significant analysis or data flaws. In this paper, we identify many of the common challenges that analysts face when using XPS for battery materials, pointing to recent literature that addresses many of the critical issues associated with sample preparation, data collection and analysis. A common error for battery materials (among others) involves ignoring peak overlap and interference. Specifically, when a minor peak associated with one component overlaps or contributes to a major peak (or one recommended for quantitative analysis) from another element in the material. Overlap issues apply to electrodes involving many elements with complex photoelectron peak structures, and also those involving peaks with seemingly simpler spectral envelopes such as Li and F. Examples of issues associated with battery systems are highlighted by discussion of challenges associated with XPS analysis of Li and Nickle-Manganese-Cobalt (NMC) electrodes in battery systems. Lithium has particular challenges associated with preparation and sometimes unexpected peak overlap with F. In our laboratory, and in the literature, NMC electrodes are often examined and new XPS users do not always recognize interference of the Auger signal from F (in or on the electrode) with Ni 2p photoelectron spectrum when generated with Al ka X-rays. The use of simulated spectra involving both F and NiO demonstrates the extent of F Auger contributions to the Ni 2p signal strength as a function of the F/Ni atom ratio in the material and suggests spectra information that can be used to identify how significant effects will be on the resultant spectra. Comparison of the results from the synthesized spectra to F/Ni ratios from actual NMC electrodes shows that in many cases overlap issues are significant.