XPS on Li-Battery-Related Compounds: Analysis of Inorganic SEI Phases and a Methodology for Charge Correction

Abstract

Accurate identification of chemical phases associated with the electrode and solid-electrolyte interphase (SEI) is critical for understanding and controlling interfacial degradation mechanisms in lithium-containing battery systems. To study these critical battery materials and interfaces Xray photoelectron spectroscopy (XPS) is a widely used technique that provides quantitative chemical insights. However, due to the fact that a majority of chemical phases relevant to battery interfaces are poor electronic conductors, phase identification that relies primarily on absolute XPS core level binding-energies (BEs) can be problematic. Charging during XPS measurements leads to BE shifts that can be difficult to correct. These difficulties are often exacerbated by the coexistence of multiple Li-containing phases in the SEI with overlapping XPS core levels. To facilitate accurate phase identification of battery-relevant phases (and electronically insulating phases in general), we propose a straightforward approach for removing charging effects from XPS data sets. We apply this approach to XPS data sets acquired from six battery-relevant inorganic phases including lithium metal (Li 0 ), lithium oxide (Li2O), lithium peroxide (Li2O2), 2 lithium hydroxide (LiOH), lithium carbonate (Li2CO3) and lithium nitride (Li3N). Specifically, we demonstrate that BE separations between core levels present in a particular phase (e.g. BE separation between the O 1s and Li 1s core levels in Li2O) provides an additional constraint that can significantly improve reliability of phase identification. For phases like Li2O2 and LiOH where the Li-to-O ratios and BE separations are nearly identical, x-ray excited valence-band spectra can provide additional clues that facilitate accurate phase identification. We show that in-situ growth of Li2O on Li 0 provides a means for determining absolute core level positions, where are all charging effects are removed. Finally, as an exemplary case we apply the charge-correction methodology to XPS data acquired from a symmetric cell based on a Li2S-P2S5 solid electrolyte.This analysis demonstrates that accurately accounting for XPS BE shifts as a function of currentbias conditions can provide a direct probe of ionic conductivities associated with battery materials.

Surface‐Driven Energy Storage Behavior of Dual‐Heteroatoms Functionalized Carbon Material

“…Figure b–d displays the high‐resolution XPS spectra of Li 1s, O 1s, and S 2p for OS–C at the discharged state (1.0 V) in the LIB system. Compared to that at the final charged stage (Figure e–g), the Li 1s spectra are slightly shifted to higher binding energies, providing additional information for the lithiation/delithiation of functional groups. Although the difference of Li 1s between discharged and charged OS–C electrode is not clear (Figure b,e), the peak shapes of O 1s are distinctly different in the two states (Figure c,f).…”

“…Although the difference of Li 1s between discharged and charged OS–C electrode is not clear (Figure b,e), the peak shapes of O 1s are distinctly different in the two states (Figure c,f). In the discharged state (1.0 V), the O 1s spectrum can mainly be deconvoluted into three components, and the two peaks at 531.0 and 532.4 eV reveal the stable presence of SO and CO bonds, respectively, while the appearance of an additional peak at 530.0 eV can be assigned to the electrostatic attraction of CO − and Li + (LiOC), and the CO − is oxidized to CO (quinoid unit) with higher binding energy (530.0 eV) after charged to 3.0 V (Figure f) . Furthermore, Li + is intercalated into OS–C, where two peaks come together at 163.3 and 164.5 eV, representing CSLi rise as the SS bond is decomposed.…”

Extended Interfacial Stability through Simple Acid Rinsing in a Li-Rich Oxide Cathode Material

“…The Li 1s spectrum ( Figure 4A) of the as-received sample consists of a major peak centered at 53.9 eV assigned to the lithiated transition metal oxide, and a small shoulder centered around 55.4 eV assigned to Li2CO3. 34 In the surface-treated powder, the peak corresponding to the lithium in the transition metal oxide is of reduced intensity, which provides evidence for a partial Li + While the small shift in Mn 2p XPS implies the reduction of Mn on the surface, a more direct probe of the Mn 3d valence states is needed to clarify and quantify the Mn states. It is known that soft X-ray absorption spectra (sXAS) of TM L-edges provide a much more direct probe of the Mn 3d valence states instead of the small chemical potential shift in XPS.…”

Stable Potassium Metal Anodes with an All‐Aluminum Current Collector through Improved Electrolyte Wetting

“…The C 1s peak can be fitted into four separated peaks of CC (284.5 eV), CO (286.5 eV), CO (287.9 eV), and OCO (289.2 eV). [48] The F 1s spectra exhibit two peaks around 682.8 (KF) and 686.8 eV (CF). [20,21,49] It needs to be mentioned that there is a slight shift of the C 1s peak energy with increasing cycling number, and the raw XPS data is provided in Figure S28, Supporting Information.…”