In Vacuo Scratching\nYields Undisturbed Insight into\nthe Bulk of Lithium-Ion Battery Positive Electrode Materials

Characterizing Li-ion battery (LIB) materials by X-ray\nphotoelectron\nspectroscopy (XPS) poses challenges for sample preparation. This holds\nespecially true for assessing the electronic structure of both the\nbulk and interphase of positive electrode materials, which involves\nsample extraction from a battery test cell, sample preparation, and\nmounting. Here, we introduce the method of in vacuo scratching as\npreparation for XPS measurements of LIB positive electrode materials,\nwhich can drastically reduce spectral contaminations and enhance spectral\nquality, enabling higher information gain. The benefits of this effective\nyet simple method are highlighted in comparison to Ar<sup>+</sup>-sputtering\nand air contact using commercially applied powder LiNi<sub>1/3</sub>Mn<sub>1/3</sub>Co<sub>1/3</sub>O<sub>2</sub> (NMC333) as showcase\nmaterial. For assessing interphase formation, the electrode material\nwas soaked in electrolyte, and the effects of rinsing and in vacuo\nscratching were studied. This treatment results in high signal-to-noise\nspectra, yielding well-defined photoelectron spectra without the influence\nof the interphases and spectral artifacts from, e.g., Ar<sup>+</sup> sputtering.