XPS Analysis of K‑based Reference Compounds to Allow Reliable Studies of Solid Electrolyte Interphase in K‑ion Batteries

As for Li- and Na-ion batteries, the electrolyte reactivity (i.e., the salt and solvent decomposition) also plays a crucial role in the electrochemical performance of K-ion batteries (KIBs). However, X-ray photoelectron spectroscopy (XPS) analysis of a solid electrolyte interphase (SEI) in KIBs remains based on Li-ion and Na-ion literature so far. This may lead to incorrect interpretations of the results considering that the first ionization potential difference between the alkali metals is expected to significantly change the binding energy values observed by XPS for a given M-based (M = Li, Na, or K) compound. Therefore, this work aims at providing XPS characterization of numerous commercial K-based reference compounds, including some that were still missing in the literature. In particular, absolute and relative binding energy values are given and compared to corresponding Li and Na counterparts. This work will thus help researchers to get reliable XPS analysis of the SEI in KIBs.