XPS Peak-Fitting of 2H MoS ₂ , 1T MoS ₂ , and MoS _2-X Nanosheets in MoS ₂ Powders and Battery Electrodes After Ar ⁺ Ion Depth-Profiling

The two common characterization techniques that can distinguish between the metastable 1T and stable 2H phase of molybdenum disulfide (MoS₂) are Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Argon ion etching within XPS offers the possibility to explore sample composition as a function of depth. However, for 2H MoS₂ samples this results in sample alteration via the creation of sulfur vacancies and leads to local areas of MoS_2‑<i>x</i> and 1T/2H MoS₂. XPS MoS_2‑<i>x</i> generation (228.1 eV) and laboratory nanoscale 1T MoS₂ synthesis (228.4 eV) are easily mistaken in XPS, as both signals exhibit downshifted Mo 3d binding energies relative to 2H MoS₂ (229.3 eV). Thus, we applied a four split orbit peak XPS model that enables distinction between MoS_2‑<i>x</i> alteration and successful 1T phase synthesis. In argon etching induced MoS_2‑<i>x</i> the pristine S 2p peaks remain dominant (162.0 eV) and the S/Mo atomic ratio decreases from 2.5 to 1.1 after electrode ion bombardment. When nanoscale 1T MoS₂ forms during lithiation in a lithium-ion battery, the dominant S 2p peaks are found at lower binding energies (161.5 eV) and the S/Mo atomic ratio is elevated (>2.0). Depth profiling of ex situ 1T/2H MoS₂ electrodes showcases lithiation beyond the electrode surface, clearly distinguished from solely MoS_2‑<i>x</i> alteration through the S 2p component percentage, which exceeds the 1T MoS₂ limiting threshold (1T > 13% of S 2p) for ion bombarding of as-cast electrodes.