X-ray Absorption Spectra of Dissolved Polysulfides in Lithium-Sulfur Batteries from First-Principles.
The X-ray absorption spectra (XAS) of lithium polysulfides (Li2Sx) of various chain lengths (x) dissolved in a model solvent are obtained from first-principles calculations. The spectra exhibit two main absorption features near the sulfur K-edge, which are unambiguously interpreted as a pre-edge near 2471 eV due to the terminal sulfur atoms at either end of the linear polysulfide dianions and a main-edge near 2473 eV due to the (x - 2) internal atoms in the chain, except in the case of Li2S2, which only has a low-energy feature. We find an almost linear dependence between the ratio of the peaks and chain length, although the linear dependence is modified by the delocalized, molecular nature of the core-excited states that can span up to six neighboring sulfur atoms. Thus, our results indicate that the ratio of the peak area, and not the peak intensities, should be used when attempting to differentiate the polysulfides from XAS.
Tod A
TA
Pascal
Kevin H
KH
Wujcik
Juan
J
Velasco-Velez
Chenghao
C
Wu
Alexander A
AA
Teran
Mukes
M
Kapilashrami
⊥Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, United States.
Jordi
J
Cabana
Jinghua
J
Guo
Miquel
M
Salmeron
Nitash
N
Balsara
David
D
Prendergast
K-edge; XAS; electronic screening; energy storage; excited state; renewable