In Vacuo Scratching Yields Undisturbed Insight into the Bulk of Lithium-Ion Battery Positive Electrode Materials

Abstract

Characterizing Li-ion battery (LIB) materials by X-ray photoelectron spectroscopy (XPS) poses challenges for sample preparation. This holds especially true for assessing the electronic structure of both the bulk and interphase of positive electrode materials, which involves sample extraction from a battery test cell, sample preparation, and mounting. Here, we introduce the method of in vacuo scratching as preparation for XPS measurements of LIB positive electrode materials, which can drastically reduce spectral contaminations and enhance spectral quality, enabling higher information gain. The benefits of this effective yet simple method are highlighted in comparison to Ar⁺-sputtering and air contact using commercially applied powder LiNi_1/3Mn_1/3Co_1/3O₂ (NMC333) as showcase material. For assessing interphase formation, the electrode material was soaked in electrolyte, and the effects of rinsing and in vacuo scratching were studied. This treatment results in high signal-to-noise spectra, yielding well-defined photoelectron spectra without the influence of the interphases and spectral artifacts from, e.g., Ar⁺ sputtering.