X-ray photoelectron spectroscopy analysis of reference compounds for studying rechargeable Li-, Na-, and K-ion batteries

Having reliable reference spectra is essential for interpreting X-ray photoelectron spectroscopy (XPS) data, especially of battery materials. However, inconsistencies in calibration, sample preparation, and spectral assignment have limited cross-comparisons between studies. In this work, we built a comprehensive reference library applicable to both laboratory XPS and hard X-ray photoelectron spectroscopy (HAXPES) for the key components of Li-, Na-, and K-ion batteries, including electrode materials, polymeric binders, and electrolyte salts or their decomposition products. Conductive composite films were prepared to minimise charge-up effects, and an Os coating was selectively applied to highly insulating compounds. The library provides a unified benchmark for spectral assignment in both HAXPES and conventional XPS, facilitating a more reliable interpretation of the solid-electrolyte interphase and surface chemistries of next-generation rechargeable batteries.