Advantages and Limitations of X-ray Photoelectron Spectroscopy in Battery Research: A Case Study of Lithium bis(Trifluoromethane)Sulfonimide (LiTFSI)

X-ray Photoelectron Spectroscopy (XPS), a surface-sensitive technique with atomic-scale sensitivity, provides unique insights into the elemental composition, as well as the chemical and electronic states of elements within a material. Given its ability to analyze surfaces with high precision, XPS has become a prominent tool in battery research. Despite its numerous advantages and high reliability, XPS has certain limitations caused by experimental requirements. Factors such as X-ray radiation, high vacuum conditions, and necessity for charge neutralization can potentially alter the sample composition during analysis, leading to misinterpretations of artificial reaction products as genuine battery reactions processes. This concern is particularly critical in the analysis of nonaqueous battery systems containing liquid electrolytes, where volatile components are highly sensitive to vacuum conditions and X-ray exposure. In this study, we systematically investigate the effects of XPS conditions on Lithium bis(Trifluoromethane)Sulfonimide (LiTFSI), a widely used component in nonaqueous battery electrolytes. We demonstrate how prolonged vacuum exposure, application of a low-energy electron flood gun (eFG) and extended X-ray irradiation contribute to the continuous degradation of LiTFSI. Additionally, we propose partial solutions to mitigate these decomposition processes, thereby improving the reliability of XPS measurements in battery research.