Understanding the Charging Mechanism of Lithium-Sulfur Batteries Using Spatially Resolved Operando X-Ray Absorption Spectroscopy

Gorlin, Yelena; Patel, Mrinali; Freiberg, Anna T. S.; Qi, He; Piana, Michele; Tromp, Moniek; Gasteiger, Hubert A.

doi:10.1149/2.0631606jes

Cited by 118 publications

(145 citation statements)

References 41 publications

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“…An additional map was collected at 2477.5 eV, which corresponds to a higher order polysulfide spectral feature, to aid in fitting (discussed in the "XANES Fitting" section). These values were taken from literature [35][36][37]41 as well as from spectra taken in this experiment at various points on the battery cell before cycling. These energies are denoted on an S 8 standard spectrum in Figure 3.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, most X-ray characterization is performed through the thickness of the battery electrodes, giving an average of the chemistry throughout the cell. While some cross-sectional work has been done, 36,37 it has been limited to XAS rather than spectromicroscopy experiments.In this paper, we present X-ray spectromicroscopy of a crosssectional Li-S battery that presents a spatially resolved chemical picture of the electrodes and electrolyte during galvanostatic cycling. From these measurements, the condition of the electrode at different states of charge can be qualitatively compared; furthermore, with the use of standards and image processing methods, the concentrations of sulfur species can be quantitatively analyzed.…”

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confidence: 99%

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Operando Spectromicroscopy of Sulfur Species in Lithium-Sulfur Batteries

Miller

Kasse

Heath

et al. 2017

J. Electrochem. Soc.

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In this study, a novel cross-sectional battery cell was developed to characterize lithium-sulfur batteries using X-ray spectromicroscopy. Chemically sensitive X-ray maps were collected operando at energies relevant to the expected sulfur species and were used to correlate changes in sulfur species with electrochemistry. Significant changes in the sulfur/carbon composite electrode were observed from cycle to cycle including rearrangement of the elemental sulfur matrix and PEO 10 LiTFSI binder. Polysulfide concentration and area of spatial diffusion increased with cycling, indicating that some polysulfide dissolution is irreversible, leading to polysulfide shuttle. Fitting of the maps using standard sulfur and polysulfide XANES spectra indicated that upon subsequent discharge/charge cycles, the initial sulfur concentration was not fully recovered; polysulfides and lithium sulfide remained at the cathodes with higher order polysulfides as the primary species in the region of interest. Quantification of the polysulfide concentration across the electrolyte and electrode interfaces shows that the polysulfide concentration before the first discharge and after the third charge is constant within the electrolyte, but while cycling, a significant increase in polysulfides and a gradient toward the lithium metal anode forms. This chemically and spatially sensitive characterization and analysis provides a foundation for further operando spectromicroscopy of lithium-sulfur batteries. New "beyond lithium-ion" battery chemistries are essential to meet the increasing demand for long-lasting, high capacity energy storage in portable electronics and electric vehicles. Lithium-sulfur (Li-S) batteries are an attractive Li-ion alternative that provides large capacity (1672 mAh g −1 ) and energy density (2500 Wh kg −1 ) while also being low cost, earth-abundant, and lightweight.1-3 Li-S batteries have a unique chemistry that achieves high capacity via chemical transformation rather than Li intercalation. Elemental sulfur (S 8 ) is reduced through a series of soluble Li polysulfides (Li 2 S x , 2 ≤ x ≤ 8) to a final solid discharge product (Li 2 S), and the process is reversed upon charging. [4][5][6] However, Li-S suffers from unrealized theoretical capacity and rapid capacity fade due to loss processes that are not well-understood. 2,7 While many advances in electrode and electrolyte engineering have been made in an attempt mitigate these performance issues, 8-14 a gap remains in the mechanistic understanding of Li-S battery operation. Several mechanisms for reduced capacity and capacity fade have been proposed. Lithium polysulfides, which are necessary for operation, dissolve into the liquid electrolyte, remain dissolved, and "shuttle" between the electrodes rather than participating in the electrochemical reactions, decreasing the amount of active material available. 3,[15][16][17][18] Low sulfur utilization results in initially low capacity that then continues to decrease with subsequent cycles. [19][20][21] Batteries are spatiall...

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Section: Resultsmentioning

confidence: 99%

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Operando Spectromicroscopy of Sulfur Species in Lithium-Sulfur Batteries

Miller

Kasse

Heath

et al. 2017

J. Electrochem. Soc.

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“…The spontaneous sulfur reaction with lithium passes through several reactions that determine the production of radicals and moieties which, within the total reaction, can be expressed in the formula S 8 +16 Li + ⇄8 Li 2 S. In fact, the pristine octa‐sulfur ring reacts with lithium ions during the discharge processes, producing lithium polysulfides with different chain lengths and leading to the insulated Li 2 S species at the end of the discharge process . This conversion reaction is even more complex owing to the phase change of the reaction products, from solid to liquid, during the voltage drop from 2.4 to 2.1 V along the discharge profile . The liquid polysulfides are soluble in common electrolytes, leading to loss of active material from the electrode, and hence, fast capacity fading upon cycling .…”

Section: Introductionmentioning

confidence: 99%

High‐Sulfur‐Content Graphene‐Based Composite through Ethanol Evaporation for High‐Energy Lithium‐Sulfur Battery

et al. 2019

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Lithium‐sulfur batteries are the most promising candidates for next‐generation energy storage devices owing to their high theoretical specific capacity of 1675 mAh g−1 and high theoretical energy density of approximately 3500 Wh kg−1. However, the lack of cathode active materials with appropriate electrical conductivities and stability coupled with an inexpensive and industrially compatible production process has so far hindered the development of practical devices. Here, a facile preparation pathway is reported for the production of a sulfur–carbon composite active material by drying a mixture of highly conductive few‐layer graphene (FLG) flakes (produced by exploiting an innovative wet jet milling process with a yield of ≈100 % and production capability of ≈23.5 g h−1) with elemental sulfur, using ethanol as an environmentally friendly solvent. The designed sulfur–FLG composite shows excellent electrochemical results. The assembled lithium–sulfur battery exhibits a stable rate capability up to a current rate of 2C, a coulombic efficiency approaching 100 % for 300 cycles at the current rate of C/4 (420 mA g−1), and a long cycle life up to 500 cycles delivering around 600 mAh g−1 at 2C (3350 mA g−1).

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“…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.…”

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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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Understanding the Charging Mechanism of Lithium-Sulfur Batteries Using Spatially Resolved Operando X-Ray Absorption Spectroscopy

Cited by 118 publications

References 41 publications

Operando Spectromicroscopy of Sulfur Species in Lithium-Sulfur Batteries

Operando Spectromicroscopy of Sulfur Species in Lithium-Sulfur Batteries

High‐Sulfur‐Content Graphene‐Based Composite through Ethanol Evaporation for High‐Energy Lithium‐Sulfur Battery

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

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