Lithium Sulfur Battery: Oxidation/Reduction Mechanisms of Polysulfides in THF Solutions

Yamin, H.; Gorenshtein, A.; Penciner, J.; Sternberg, Y.; Peled, E.

doi:10.1149/1.2095868

Cited by 459 publications

(346 citation statements)

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“…26 The X-ray spectra of the reactant and expected final product, S 8 and Li 2 S, are shown in Figure 5b. The spectrum of Li 2 S is based on first principle calculations; the similarity of the theoretical Li 2 S spectrum to the established experimental spectrum for Li 2 S validates the methods used to calculate the spectra of lithium polysulfide dianion species.…”

Section: Resultsmentioning

confidence: 99%

“…f S 8 8 + f P S,T x avps [10] y P S,T = f P S,T x avps f S 8 8 + f P S,T x avps [11] The mole fractions of S 8 and polysulfide dianions are referred to as y S 8 and y P S,T , respectively. It is then convenient to determine the amount of lithium that has reacted with sulfur as a function of capacity, which we do in Equation 12:…”

Section: Resultsmentioning

confidence: 99%

“…8 (27) Calculated mole fraction of elemental sulfur that would remain assuming the hypothetical reaction shown in Equation 27 y P S, T Mole fraction of polysulfide dianion species in the back of the cathode y S 8 Mole fraction of elemental sulfur in the back of the cathode y P S, D Mole fraction of polysulfide dianions in the back of the cathode as a result of diffusion y P S,0…”

Section: Discussionmentioning

confidence: 99%

“…[3][4][5][6][7][8] One example of an electrochemical reaction pathway is: S 8(s) + 2Li + + 2e − → Li 2 S 8 [2] 3/4 Li 2 S 8 + 1/2Li + + 1/2e − → Li 2 S 6 [3] 2/3 Li 2 S 6 + 2/3Li + + 2/3 e − → Li 2 S 4 [4] 1/2 Li 2 S 4 + Li + + e − → Li 2 S 2 [5] 1/2 Li 2 S 2 + Li + + e − → Li 2 S (s) [6] 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: 9 S 8 + 2Li 2 S 4 → 2Li 2 S 8 [7] The evolution of polysulfide chain length in the presence of both electrochemical and chemical reactions is difficult to predict.…”

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confidence: 99%

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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.

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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...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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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.

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“…LiPS, while necessary for battery operation, are likely a critical factor in degradation processes; thus, deciphering the speciation and spatial distribution of dissolved LiPS in the electrodes and electrolyte is essential for future battery designs. LiPS are known to dissociate or react with each other to form intermediate species in the electrolyte [1,2]; therefore, operando characterization is necessary to understand the conditions and locations in which LiPS form before additional reactions occur. Operando X-ray absorption spectroscopy has been performed on Li-S in both conventional and cross-sectional geometries [3][4][5], but literature on operando mapping is limited [6,7].…”

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confidence: 99%

Using X-ray Spectromicroscopy for Operando Characterization of Li-S Batteries

et al. 2018

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Li-S batteries are a "beyond Li-ion" technology that delivers large capacity (1672 mAh g -1 ) while also being earth-abundant, lightweight, and low cost. Li-S achieves high capacity via a chemical transformation mechanism rather than Li intercalation as in Li-ion. Elemental sulfur S8 is reduced through a series of soluble chain-like polysulfides (LiPS; Li2Sx, 2≤x≤8) to a final solid discharge product Li2S; this reaction is reversed on charging. However, Li-S suffers from unrealized theoretical capacity and capacity fade due to loss mechanisms that are not well understood. LiPS, while necessary for battery operation, are likely a critical factor in degradation processes; thus, deciphering the speciation and spatial distribution of dissolved LiPS in the electrodes and electrolyte is essential for future battery designs. LiPS are known to dissociate or react with each other to form intermediate species in the electrolyte [1,2]; therefore, operando characterization is necessary to understand the conditions and locations in which LiPS form before additional reactions occur. Operando X-ray absorption spectroscopy has been performed on Li-S in both conventional and cross-sectional geometries [3][4][5], but literature on operando mapping is limited [6,7]. In addition, the solid electrolyte interphase (SEI), a surface film that forms on electrodes, is largely mysterious, especially in newer Li-S chemistries such as those with a polyethylene oxide binder.In this study, ex situ and operando spectromicroscopy at the sulfur K-edge (2472 eV) are used to study the SEI on Li metal and LiPS during cycling. All batteries consisted of Li metal foil with a sulfur/carbon composite thin film electrode (average sulfur loading = 6 mg cm -2 ) on carbon-coated aluminum foil. For ex situ characterization, the conventional electrolyte chemistry of 1 M bis(trifluoromethane)sulfonimide Li salt (LiTFSI) with 0.3 M LiNO3 in a 1:1 mixture by volume of 1,3-dioxolane and 1,2-dimethoxyethane (DOL/DME) was used. For operando measurements, an electrolyte solution of 1 M LiClO4, another common battery salt, with 0.2 M LiNO3 in DOL/DME was used to eliminate the signal from the sulfurcontaining LiTFSI salt. Thus, any detected sulfur signal originated from the sulfur species in the electrode.Ex situ characterization was performed on Li foil removed from a cycled coin cell to determine the composition of the surface films, shown in Figure 1. The energies in (a), (b), and (c) correspond to LiPS, Li2S, and LiTFSI, respectively. These maps demonstrate that even at low current (0.04 mA cm -2 ), active material is lost to deposition of Li2S on the electrode surface.Because the diffusion behavior of the LiPS across the electrolyte is of great interest, a cross-sectional cell (Figure 2) was designed to track LiPS in the separator/electrolyte and cathode region. Figure 3 shows the discharge/charge curve of a cross-sectional battery along with LiPS maps taken at 2470.35 eV [7]. Significant microstructural changes are seen in the electrode, even during the first d...

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The Application of Polychalcogenide Salts to the Exploratory Synthesis of Solid State Multinary Chalcogenides at Intermediate Temperatures

Kanatzidis

Sutorik

1995

Progress in Inorganic Chemistry

165

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Lithium Sulfur Battery: Oxidation/Reduction Mechanisms of Polysulfides in THF Solutions

Cited by 459 publications

References 10 publications

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

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

Using X-ray Spectromicroscopy for Operando Characterization of Li-S Batteries

The Application of Polychalcogenide Salts to the Exploratory Synthesis of Solid State Multinary Chalcogenides at Intermediate Temperatures

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