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

Pascal, Tod A.; Wujcik, Kevin H.; Velasco-Vélez, Juan-Jesús; Wu, Chenghao; Teran, Alexander A.; Kapilashrami, Mukes; Cabana, Jordi; Guo, Jinghua; Salmerón, Miquel; Balsara, Nitash P.; Prendergast, David

doi:10.1021/jz500260s

Cited by 144 publications

(234 citation statements)

References 36 publications

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“…Although we also attempted to synthesize Li 2 S 4 powder, it could not be isolated, because it is thermodynamically unstable. 27,40 Since the XANES features of Na 2 S 4 (27,28) are similar to the predicted features of lithium polysulfides, 29 it is a suitable reference for a qualitative analysis.…”

Section: Methodsmentioning

confidence: 85%

“…Although the spectra of other polysulfides such as S 3 2− , S 5 2− , S 6 2− , S 8 2− are not presented in this study, the positions of their XANES features are expected to be well represented by the spectrum of S 4 2− polysulfide. [27][28][29] This is rationalized by a computational study, which has demonstrated that the charge on a polysulfide chain migrates toward the two terminal sulfur atoms. 29 This phenomenon leads to a sulfur K-edge XANES signal consisting of two features, with the first feature at ∼2470-1 eV corresponding to the negatively charged terminal sulfur atoms and the second feature at ∼2472-3 eV corresponding to the uncharged ('neutral') internal sulfur atoms.…”

Section: Validation Of Operando Characterization Of Intermediates-mentioning

confidence: 97%

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Operando Characterization of Intermediates Produced in a Lithium-Sulfur Battery

Gorlin

Siebel

Piana

et al. 2015

J. Electrochem. Soc.

105

156

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One of the technological barriers to electrification of transport is the insufficient storage capacity of the Li-ion batteries on which the current electric cars are based. The lithium-sulfur (Li-S) battery is an advanced technology whose successful commercialization can lead to significant gains in the storage capacity of batteries and promote wide-spread adoption of electric vehicles. Recently, important Li-S intermediates, including polysulfides, S 3•-, and Li 2 S, have been shown to present unique X-ray absorption near edge structure (XANES) features at the sulfur K-edge. As a result, a combination of XANES characterization with electrochemistry has the potential to contribute to the understanding of Li-S chemistry. In this study, we present an operando XANES cell design, benchmark its electrochemical and spectroscopic performance, and use it to track reaction intermediates during the discharge of the battery. In particular, by employing electrolyte solvents with either a high or a low dielectric constant, we investigate the influence of the solvent on the conversion of polysulfide species to Li 2 S. Our results reveal that Li 2 S is already formed after ∼25-30% discharge in both types of electrolyte solvents, but that further conversion of polysulfides to Li 2 S proceeds more rapidly in a solvent with a low dielectric constant. Electric vehicles represent a promising alternative to conventional transport based on an internal combustion engine and, when combined with renewable energy sources, have the potential to decrease worldwide CO 2 emissions by 20-30%.1,2 In recent years, they have been gaining popularity in the form of passenger cars, with the number of sold units surpassing the 100,000 mark in 2012.2 One of the main technological barriers to an even wider adoption of electric cars and a complete displacement of the CO 2 -emitting vehicles is the insufficient storage capacity of the current battery technology, which leads to a limited vehicle driving range.2,3 The useable energy density of state-of-the-art lithium-ion batteries employed in recent electric vehicles amounts to only ≈120 Wh/kg system , 4 which corresponds to a practical driving range of 150-200 km. If one succeeds in the development of sufficiently durable high-voltage or high-energy cathode materials and combines them with silicon anodes, an energy density of ≈250 Wh/kg system would be in reach. 4 An alternative promising battery concept is the lithium-sulfur (Li-S) battery.3,5-7 Current development in Li-S battery research includes successful commercialization of Li-S cells with 260 Wh/kg system energy density by Sion Power corporation.8 This value already exceeds the DOE target for 2022 (250 Wh/kg system ) 9 and has the potential to also comply with the system cost target of 125 USD/kWh 9 because of the abundance and low cost of sulfur. To achieve even greater gains in the performance and, most importantly, to improve the cycle life of Li-S batteries, it will be necessary to gain a deeper mechanistic understanding of the 16 e -/S 8 in...

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Section: Methodsmentioning

confidence: 85%

Section: Validation Of Operando Characterization Of Intermediates-mentioning

confidence: 97%

Operando Characterization of Intermediates Produced in a Lithium-Sulfur Battery

Gorlin

Siebel

Piana

et al. 2015

J. Electrochem. Soc.

105

156

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“…Early theoretical work predicted slight variations in the position of the lithium polysulfide pre-edge peak in the adsorption spectra. 23 By using Resonant Inelastic X-ray Scattering (RIXS) no shifts were observed for the set of reference samples, neither within operando measurement. 24 Nevertheless, information gathered from operando XAS measurements can serve as a reliable indicator of changes within the Li-S battery upon operation.…”

mentioning

confidence: 99%

Polysulfides Formation in Different Electrolytes from the Perspective of X-ray Absorption Spectroscopy

Dominko

Vižintin

Aquilanti

et al. 2017

J. Electrochem. Soc.

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Li-S batteries are promising energy storage technology for the future, however there two major problems remained which need to be solved before successful commercialization. Capacity fading due to polysulfide shuttle and corrosion of lithium metal are directly connected with the type and quantity of electrolyte used in the cells. Several recent works show dependence of the electrochemical behavior of Li-S batteries on type of the electrolyte. In this work we compare and discuss a discharge mechanism of sulfur conversion in three different electrolytes based on measurements with sulfur K-edge XAS. The sulfur conversion mechanism in the ether based electrolytes, the most studied type of solvents in the Li-S batteries, which are enabling high solubility of polysulfides are compared with the fluorinated ether based electrolytes with a reduced polysulfide solubility and in carbonate based electrolytes with the sulfur confined into a ultramicroporous carbon. In all three cases the sulfur reduction proceeds through polysulfide intermediate phases with a difference on the type polysulfides detected at different steps of discharge. Electrification of road transport has increased the pressure on materials' scientists to improve performance of the current Li-ion batteries and to develop new advanced high energy battery technologies. 1Among several post lithium-ion technologies, the lithium sulfur (Li-S) batteries are recognized as the most promising for commercialization in the near future. A combination of lithium and sulfur in the electrochemical cell corresponds to the theoretical energy density of 2600 Wh/kg, while the maximum practically accessible energy density is predicted to be close to 600 Wh/kg.2,3 This is much higher compared to Li-ion batteries and besides that, sulfur is inexpensive and naturally abundant. Nevertheless, problems related to the solubility of polysulfides in the electrolyte and the related redox shuttle phenomena cause short cycle life, potential safety problems, poor cycling efficiency, and relative fast self-discharge. Additional problems of Li-S batteries are very low electronic conductivity of the both end members in the discharge and charge process (i.e. sulfur and Li 2 S) and extensive corrosion of the metal lithium anode.Different directions how to improve Li-S battery cycle life have been explored, like synthesis of the optimized porous host matrices with active sites for polysulfide anchoring, 4,5 design and optimization of separators which can effectively suppress polysulfide cross communication between electrodes 6,7 and protection of lithium by artificial SEI 8 or by additives. 9 While most of the research was performed in the binary mixture of solvents using alkyl ethers (glymes) and heterocyclic acetyl (dioxolane), less attention has been paid to the development of new electrolytes for Li-S batteries. 10 Reasons for that are nested in the requirements which should be fulfilled in the development of new formulations. First of all, electrolytes used in the electrochemical cells must...

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“…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

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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.

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

Cited by 144 publications

References 36 publications

Operando Characterization of Intermediates Produced in a Lithium-Sulfur Battery

Operando Characterization of Intermediates Produced in a Lithium-Sulfur Battery

Polysulfides Formation in Different Electrolytes from the Perspective of X-ray Absorption Spectroscopy

Liquid Sulfur Impregnation of Microporous Carbon Accelerated by Nanoscale Interfacial Effects

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