For a further expansion of renewable energies, a large amount of storage capacity is required. To control large-scale batteries and optimize battery materials it is necessary to understand the working principle and limitations of current state lithium-ion batteries in more detail.

This has been investigated in previous work of our group focusing on thin film batteries [1], [2] and composite materials under electrochemical cycling [3], we are aiming now to bridge the gap to real-world application materials. For this purpose commercial LiNi0.33Mn0.33Co0.33O2 (NMC333) powder was investigated by quasi-in situ photoelectron spectroscopy (XPS) i.e performing charge/discharge on battery cells and transporting the cathode to XPS without contact to air. High-resolution core level spectra were acquired for applied potentials between 3.3 V and 4.8 V vs. Li+/Li.

In this study, XPS is used to identify the chemical species formed at the solid cathode electrolyte interface (CEI). While this solid CEI is stable under the regular voltage window ( 4.2 V vs. Li+/Li), the solid CEI cannot prevent cathode decompositions at higher voltages [4],[5]. The CEI composition changes at different voltages are verified and their origin is explained based on possible interface reactions. Additionally, the 2p spectra of the transition metals are discussed in terms of charge-transfer satellite and multiplet theory and compared to reference materials to track changes in the oxidation states vs charge/discharge states of the cathode material. In-vacuo scratching makes it furthermore possible to get insights into the properties of the bulk material. Performance of different cathode materials, an impact of coating or doping, cathode blends, the influence of electrolyte compositions and additives, novel electrolytes or special battery conditions can be understood through comparison to this standard condition.