X-ray Absorption Spectra of Dissolved Polysulfides in Lithium-Sulfur Batteries from First-Principles

Area of Science:

• Computational Chemistry
• Materials Science
• Spectroscopy

Background:

• Lithium polysulfides (Li2Sx) are crucial intermediates in lithium-sulfur batteries.
• Understanding their structure and chain length is vital for battery performance.
• X-ray absorption spectra (XAS) offer a potential method for characterization.

Purpose of the Study:

• To computationally investigate the X-ray absorption spectra (XAS) of lithium polysulfides (Li2Sx) with varying chain lengths.
• To establish a reliable method for differentiating polysulfide chain lengths using XAS data.

Main Methods:

• First-principles calculations were employed to simulate XAS for Li2Sx species.
• Analysis focused on the sulfur K-edge absorption features.
• The relationship between spectral features and polysulfide chain length was examined.

Main Results:

• XAS spectra show distinct pre-edge and main-edge features related to terminal and internal sulfur atoms.
• A near-linear correlation was observed between the ratio of spectral peak areas and polysulfide chain length.
• The delocalized nature of core-excited states influences this linear dependence.

Conclusions:

• The ratio of peak areas in XAS spectra, not peak intensities, is a reliable indicator for determining Li2Sx chain length.
• This computational study provides a foundation for experimental characterization of lithium polysulfides.