X-ray spectroscopy as a probe for lithium polysulfide radicals

Pascal, Tod A.; Pemmaraju, C. D.; Prendergast, David

doi:10.1039/c4cp05316h

Cited by 47 publications

(60 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As shown in Figure 2c, eq 5 predicts the free energy of sulfur encapsulated in various sized nanopores, as well as at the graphene interface, to within 3% of the values calculated from MD simulations over the entire liquid temperature range ( Figure S6). As with our previous efforts, 34,35 we aim to uncover electronic structure changes upon sulfur impregnation into microporous carbon that can be exploited to both resolve the underlying physical morphologies and reveal molecular scale details of function. A previous study demonstrated that surface molecules at metal interfaces have unique electronic structure, manifested as modulations of their X-ray absorption spectra (XAS).…”

mentioning

confidence: 99%

Liquid Sulfur Impregnation of Microporous Carbon Accelerated by Nanoscale Interfacial Effects

et al. 2017

Self Cite

View full text Add to dashboard Cite

Impregnation of porous carbon matrices with liquid sulfur has been exploited to fabricate composite cathodes for lithium−sulfur batteries, aimed at confining soluble sulfur species near conducting carbon to prevent both loss of active material into the electrolyte and parasitic reactions at the lithium metal anode. Here, through extensive computer simulations, we uncover the strongly favorable interfacial free energy between liquid sulfur and graphitic surfaces that underlies this phenomenon. Previously unexplored curvaturedependent enhancements are shown to favor the filling of smaller pores first and effect a quasi-liquid sulfur phase in microporous domains (diameters <2 nm) that persists ∼30°b elow the expected freezing point. Evidence of interfacial sulfur on carbon is shown to be a 0.3 eV red shift in the simulated and measured interfacial X-ray absorption spectra. Our results elucidate the critical morphology and thermodynamic properties necessary for future cathode design and highlight the importance of molecular-scale details in defining emergent properties of functional nanoscale interfaces.

show abstract

mentioning

confidence: 99%

Liquid Sulfur Impregnation of Microporous Carbon Accelerated by Nanoscale Interfacial Effects

et al. 2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…[ 22 ] In a previous work, we demonstrated that the XAS of dissolved lithium polysulfi de dianion species can be obtained via condensed-phase fi rst-principles molecular dynamics and DFT spectral simulations. [ 21 ] More recently, we extended our approach to the various polysulfi de radicals in vacuum [ 26 ] and have predicted that XAS can detect the trisulfur radical against a background of longer chain polysulfi de dianions at a ≈20% molar concentration (or ≈4% by spectral composition) at 0.1-0.2 eV spectral resolution. Our condensed phase DFT approach has been proven accurate when compared to measured spectra of known sulfur containing compounds and is extremely insightful for interpreting spectra based on the atomic and electronic properties of the molecule of interest.…”

Section: Introductionmentioning

confidence: 99%

“…[ 21,22,26 ] Vijayakumar et al calculated the XAS of the various polysulfi des, including the trisulfur radical, in vacuum and in a solvation shell of six DMSO molecules using time-dependent DFT calculations, and used these spectra to fi ngerprint experimental measurements. [ 22 ] In a previous work, we demonstrated that the XAS of dissolved lithium polysulfi de dianion species can be obtained via condensed-phase fi rst-principles molecular dynamics and DFT spectral simulations.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Polysulfide Radicals Present in an Ether‐Based Electrolyte of a Lithium–Sulfur Battery During Initial Discharge Using In Situ X‐Ray Absorption Spectroscopy Experiments and First‐Principles Calculations

Wujcik

Pascal

Pemmaraju

et al. 2015

Advanced Energy Materials

Self Cite

119

118

View full text Add to dashboard Cite

The presence and role of polysulfide radicals in the electrochemical processes of lithium sulfur (Li–S) batteries is currently being debated. Here, first‐principles interpretations of measured X‐ray absorption spectra (XAS) of Li–S cells are leveraged with an ether‐based electrolyte. Unambiguous evidence is found for significant quantities of polysulfide radical species (LiS3, LiS4, and LiS5), including the trisulfur radical anion S3 −, present after initial discharge to the first discharge plateau, as evidenced by a low energy shoulder in the S K‐edge XAS below 2469 eV. This feature is not present in the XAS of cells at increased depth of discharge, which, by our analysis, exhibit increasing concentrations of progressively shorter polysulfide dianions. Through a combination of first‐principles molecular dynamics and associated interpretation of in situ XAS of Li–S cells, atomic level insights into the chemistries are provided that underlie the operation and stability of these batteries.

show abstract

“…26,31 In this work, in situ X-ray absorption spectroscopy at the sulfur K-edge is used to examine an Li-S cell cathode during discharge. The low energy of sulfur K-edge X-rays, and the presence of sulfur in the cathode (which absorbs sulfur K-edge X-rays) limited the penetration of X-rays into the cathode.…”

mentioning

confidence: 99%

“…[28][29][30] However, we have recently shown that the X-ray absorption spectra for lithium polysulfide molecules can be calculated from first principles, thus enabling unambiguous interpretation of experimentally obtained X-ray spectra. 26,31 In this work, in situ X-ray absorption spectroscopy at the sulfur K-edge is used to examine an Li-S cell cathode during discharge. The low energy of sulfur K-edge X-rays, and the presence of sulfur in the cathode (which absorbs sulfur K-edge X-rays) limited the penetration of X-rays into the cathode.…”

mentioning

confidence: 99%

In Situ X-ray Absorption Spectroscopy Studies of Discharge Reactions in a Thick Cathode of a Lithium Sulfur Battery

Wujcik

Wang

Pascal

et al. 2016

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Lithium sulfur (Li-S) batteries are well known for their high theoretical specific capacities, but are plagued with scientific obstacles that make practical implementation of the technology impossible. The success of Li-S batteries will likely necessitate the use of thick sulfur cathodes that enable high specific energy densities. However, little is known about the fundamental reaction mechanisms and chemical processes that take place in thick cathodes, as most research has focused on studying thinner cathodes that enable high performance. In this work, in situ X-ray absorption spectroscopy at the sulfur K-edge is used to examine the back of a 115 μm thick Li-S cathode during discharge. Our results show that in such systems, where electrochemical reactions between sulfur and lithium are likely to proceed preferentially toward the front of the cathode, lithium polysulfide dianions formed in this region diffuse to the back of the cathode during discharge. We show that high conversion of elemental sulfur is achieved by chemical reactions between elemental sulfur and polysulfide dianions of intermediate chain length ( Lithium sulfur batteries have become a widely popular focus of energy storage research due to their high theoretical specific capacity of 1672 mA-h/g. 1,2 The overall reaction mechanism that governs the Li-S discharge processes is given by:The actual reaction mechanism involves a series of electrochemical reactions with lithium polysulfide reaction intermediates (Li 2 S x , 2 ≤ x ≤ 8, referred to as polysulfide dianions; or LiS x , 3 ≤ x ≤ 5, referred to as polysulfide radical anions). [3][4][5][6][7][8] One example of an electrochemical reaction pathway is:A decrease in the chain length of polysulfides is thus an unambiguous signature of electrochemical reactions. However, polysulfides are also known to undergo chemical reactions, for example:The evolution of polysulfide chain length in the presence of both electrochemical and chemical reactions is difficult to predict. Lithium polysulfides tend to dissolve into the electrolyte, resulting in loss of cell capacity. It is thus not surprising that a great deal of research focuses on solving the issues related to polysulfide dissolution. [10][11][12][13] Many researchers have recognized that in order for Li-S cells to have high specific energy density and be competitive in cost with current lithium ion battery technology, Li-S cell cathodes must have high area-specific sulfur loadings.14-16 These high sulfur loadings can only be achieved by making the Li-S cell cathodes * Electrochemical Society Member. Increasing cathode thickness amplifies concentration polarization effects and plating of Li 2 S (and possibly Li 2 S 2 ) at the front of the electrode.18 These problems are magnified if the battery is cycled at high rates of charge and discharge.Despite their apparent importance, little is known about the chemical and electrochemical reactions that take place in thick sulfur cathodes. The purpose of this paper is to shed light on these reactions. In partic...

show abstract

X-ray spectroscopy as a probe for lithium polysulfide radicals

Cited by 47 publications

References 54 publications

Liquid Sulfur Impregnation of Microporous Carbon Accelerated by Nanoscale Interfacial Effects

Liquid Sulfur Impregnation of Microporous Carbon Accelerated by Nanoscale Interfacial Effects

Characterization of Polysulfide Radicals Present in an Ether‐Based Electrolyte of a Lithium–Sulfur Battery During Initial Discharge Using In Situ X‐Ray Absorption Spectroscopy Experiments and First‐Principles Calculations

In Situ X-ray Absorption Spectroscopy Studies of Discharge Reactions in a Thick Cathode of a Lithium Sulfur Battery

Contact Info

Product

Resources

About