Document | Reactions | Methods |
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2002_Kolosnitsyn_Cycling a Sulfur Electrode in Mixed Electrolytes Based on Sulfonlane: Effect of Ethers | The 1st discharge stage: S8 + 2 e- → S82– S82– ↔ S62– + 1/4 S8 (goes back to the prev eq) S62– ↔ 2 S3– S62– → S42– + 1/4 S8 The 2nd discharge stage: 2 S62– → S72– + S52– (chemical slow) 5 S72– + 4 e- → 7 S52– (elechtrochemical fast) 2 S52– → S72–(to prev) + S32– (chemical slow) 2 S32– → S52–(to prev) + S2– (chemical slow) |
⊕: 70 wt % of sulfur, 10 wt % of carbon, and 20 wt % of polyethylene oxide ⊖: lithium foil 200 μm thick Electrolyte: mixtures of sulfolane and such ethers as 1,2-dimethoxyethane, dioxolane, and tetrahydrofuran |
2002_Leghie_Important comments on mechanism of electrochemical reduction of sulfur in DMF | A general model: If 1 < n < 8 2 Sn2- ↔ Sn - 12- + Sn + 12- S62- ↔ 2 S3- S82- ↔ 2 S4- If n = 8 S82- ↔ S62- + 1/4 S8 (dissociation always weak) If n > 8 Sn2- → S82- + (n - 8)/8 S8 With the study of Li2S6 + DMF solutions, following mechanism is proposed: S82- ↔ S62- + 1/4 S8 2 S62- ↔ S42- + S82- S82- ↔ 2 S4- S62- ↔ 2 S3- S4- + e- ↔ S42- (- 1.30 V vs Fc+/Fc at 293 K) S3- + e- ↔ S32- (- 1.80 V vs Fc+/Fc at 293 K) In classical organic solutions, only S8 and the radical anions Sn- are reducible and only the dianions Sn2- and S8 are oxidable. |
This paper is devoted to the mechanism of the electrochemical reduction of sulphur in dimethylformamide (DMF). Many polysulphides have been characterized in the solid state by X-ray diffraction, infrared and Raman spectroscopy. Here, cyclic voltammetry and spectroelectrochemical studies are used. |
2008_Kolosnitsyn Karaseva_Lithium-Sulfur Batteries: Problems and Solutions | The 1st discharge stage: Reduction of elementary sulfur, disproportionation. S8 + 2 e- + 2 Li+ → Li2S8 Li2S8 → Li2Sn + (8 - n) S 2nd stage: 2 major schemes Decrease in the polysulfide chain length Li2Sn + 2 e- + 2 Li+ → Li2S↓ + Li2S(n - 1) Li2Sn - 1 + 2 e- + 2 Li+ → Li2S↓ + Li2S(n - 2) Li2S2 + 2 e- + 2 Li+ → 2 Li2S↓ Rapid disproportionation of Li2Sn x Li2Sn - 1 → Li2S↓ + y Li2Sn. |
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2011_Kolosnitsyn_A study of the elctrochemical processes in lithium-sulphur cells by impedance spectroscopy | Li2Sn + 2(n - 1) Li+ + 2(n - 1) e- → n Li2S↓ | By AC impedance spectroscopy ⊕: 70 wt.% sublimed sulphur, 10 wt.% Ketjenblack EC-600 JD and 20 wt.% poly(ethylene oxide) ⊖: Lithium metal foil Electrolyte: 1M LiClO4 in sulfolane |
2012_Barchasz_Lithium-Sulfur Cell Discharge Mechanism: An Original Approach for Intermediate Species Identification | Chronoamperometry Measurements: 1st step: 3 V: S82- ↔ S42- + 1/2 S8 2.4 V: S8 + 2 e- → S82- S82- ↔ S62- + 1/4 S8 S82- ↔ S52- + 3/8 S8 2.3 V: S62- → 2 S3- (dissociation) 2nd step: (detectable at high scan rates using cyclic voltammograms) 2.1 V: 2 S3- → S62- (slow) 2 S62- + 2 e- → 3 S42- (fast) 2 S42- → S52- + S32- 3rd step: 1.95 V: 3 S42- + 2 e- → 4 S32- 2 S32- + 2 e- → 3 S22- S42- + 2 e- → 2 S22- S22- + S42- ↔ 2 S32- S22- + 2 e- → 2 S2- (insoluble) The overall reaction is 16 Li + S8 → 8 Li2S A proposed mechanism is given in the paper (page 7). |
The discharge mechanism was investigated through the electrolyte characterization. Using high-performance liquid
chromatography, UV−visible absorption, and electron spin resonance spectroscopies,
we investigated the electrolyte composition at different discharge potentials in a TEGDME-based electrolyte. A 10−2mol.L−1 concentration of equivalent lithium octasulfide (Li2S8) solution was prepared in TEGDME in order to achieve the polysulfide UV band and HPLC peak attribution. |
2013_Barghamadi_Review on LiS | 16 Li + S8 → 8 Li2S I: Reaction of elemental sulfur with Li is given by: S8 + 2 Li+ + 2 e- → Li2S8 II: A reaction between dissolved Li2S8 and lithium is described as: Li2S8 + 2 Li+ + 2 e- → 2 Li2S4 III: A transition from the dissolved Li2S4 to insoluble Li2S2 or Li2S by the coexistence of following equations: Li2S4 + 2 Li+ + 2 e- → 2 Li2S2 Li2S4 + 6 Li+ + 6 e- → 4 Li2S IV: An equilibrium reaction of insoluble Li2S2 and Li2S is described as: Li2S2 + 2 Li+ + 2 e- → 2 Li2S |
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2013_Fronczek, Bessler_Insight into lithium-sulfur batteries: Elementary kinetic modeling and impedance simulation | S8 ↔ S8(ds) 1/2 S8(ds) + e- ↔ 1/2 S8(ds)2- 3/2 S82- + e- ↔ 2 S62- S62- + e- ↔ 3/2 S42- 1/2 S42- + e- ↔ S22- 1/2 S22- + e- ↔ S2- S2- + 2 Li+ ↔ Li2S |
⊕: sulfur content (>80% by weight) ⊖: lithium metal Six-step polysulfide reduction mechanism at the cathode. The modeling framework allows for the simulation of charge and discharge profiles as well as electrochemical impedance spectra. Simulations are carried out using the in-house software package DENIS (detailed electrochemistry and numerical impedance simulation). Impedance simulation is based on the full physicochemical model, including detailed chemistry and transport, without the use of equivalent circuits. Concentrations of each dissolved element during discharge are shown in the paper. |
2013_Nazar_Sulfur Speciation | XRD revealed that α-S8 and Li2S
were the only detectable nanocrystalline phases in Li2Sn
powders for n = 1, 2, and 4 and n = 4 and 8, respectively. Only Li2S6 appeared fully amorphous by XRD. Existence of Li2S2 as a solid metastable phase is not indicated by our NMR data, and Li2S6 is the only intermediate isolated between α-S8 and Li2S. Considering the number of reference spectra, multiple solutions exist, among which the LCF (linear combination fit) constructed from the minimum combination of {α-S8, S62−, S42−, and S2−} gave the bestfit and agreement with the electrochemistry. There is strong evidence for the rapid chemical disproportionation of S82− in solution based on UV spectroscopy and electrochemical techniques, S82− → S62− + 1/4 S80. The overall discharge as probed by XANES can be summarized as S0 + 3/2 Li+ + 3/2 e− → 3/4 Li2S + 1/4 S0 to account for the persistence of about 25% elemental sulfur. |
Here, we realize sulfur speciation in the cell over the full
capacity range using operando X-ray absorption near-edge
spectroscopy (XANES) by developing and utilizing a carbon−
sulfur composite electrode optimized for both efficient
transport of charge carriers and trapping of soluble polysulfides.
The cathode consists of sulfur impregnated in porous hollow
carbon spheres of uniform diameter that minimize significant
dissolution into the bulk electrolyte, paired with a nonsulfurous
electrolyte and incorporated in a cell designed to prevent dead
zones. We utilize synchrotron S K-edge absorption spectroscopy. Extremely uniform porous carbon nanospheres (PCNSs) were used. |
2013_Zhang_Liquid electrolyte lithium/sulfur battery: Fundamental chemistry problems, and solutions | The Gibbs free-energy (ΔG0) of each polysulfide anion (n = 2 ~ 8) is so close that these anions are co-existent in the solution through a series of chemical equilibriums. Region I: S8 + 2 Li → Li2S8 Region II: Li2S8 + 2 Li → Li2S8 - n + Li2Sn Region III: 2 Li2Sn + (2n - 4) Li → n Li2S2 Li2Sn + (2n - 2) Li → n Li2S Region IV: Li2S2 + 2 Li → Li2S Chemical reactions betwenn PS anions, generally: Li2Sn + Li2S → Li2Sn - m + Li2S1 + m 2 Li2Sn → Li2Sn - 1 + 1/8 S8 |
2013_Zhang_Liquid electrolyte lithium,sulfur battery:Fundamental chemistry problems, and solutions
The Gibbs free-energy of each polysulfide anion is so close that these anions are co-existent in the solution
through a series of chemical equilibriums.
Reactions are written in n-m forms, no proofs of reaction (neither its order)
2013_Nazar_Sulfur Speciation in Li−S Batteries Determined by Operando X-ray Absorption Spectroscopy
Method: Operando X-ray Absorption Spectroscopy (XANES).
Reactions and their orders are proposed. Species related: only αS8, dianions S6(2−) and S4(2−), and Li2S.
2013_Hagen_In-Situ Raman Investigation of Polysulfide Formation in Li-S Cells
Method: In-Situ Raman spectroscopy
Shift of spectrum peak in the solution, which makes sometimes difficult to identify the exact species.
Species examined: all dianions (n = 2..8) and all monoanions (n = 2..8). Comparison made for different
type of solutions. Charge and discharge spectrum prepared for THF. No exact reactions is given, but appearance
order can be shown in spectrum.
2013_Fronczek, Bessler_Insight into lithium-sulfur batteries:Elementary kinetic modeling and impedance simulation
Method: electrochemical impedance spectra, in-house software package DENIS (detailed electrochemistry and numerical
impedance simulation).
Reactions are discrete, mainly dianions, model followed Kumaresan et al. Physical (dynamic) reactions and
parameter values are proposed for simulation (one-dimensional continuum model of a Li/S cell).
Although this study demonstrates the feasibility and the potential of physicochemical modeling for understanding Li/S
electrochemistry, a proper parameterization and validation are key requirements for further conclusions.
2013_Barghamadi_A Review on Li-S Batteries as a High Efficiency Rechargeable Lithium Battery
General dianion-equations are given, but without detailed proof (can be used as a "medium" summary).
2012_Yeon_Raman Spectroscopic and X-ray Diffraction Studies of Sulfur Composite Electrodes during Discharge and Charge
Method: ex situ Raman spectroscopy and X-ray diffraction. Optical microscope images are also given in some steps.
Mainly the dianions and S3- are taken into account.
2012_Barchasz_Lithium-Sulfur Cell Discharge Mechanism:An Original Approach for Intermediate Species Identification
Method: through the electrolyte characterization. Using high-performance liquid chromatography, UV−visible absorption,
and electron spin resonance spectroscopies, we investigated the electrolyte composition at different discharge
potentials in a TEGDME-based electrolyte.
Discrete reactions for particular voltages are given. Previously mentioned dianions. "Discovoured" dianion S5
by disproportionation of dianion S8. Monoanion S3 from dissociation of dianion S6. Appearance of dianion S3.
(Even monoanion S2?)
2008_Kolosnitsyn Karaseva_Lithium-Sulfur Batteries:Problems and Solutions and
2002_Kolosnitsyn_Cycling a Sulfur Electrode in Mixed Electrolytes Based on Sulfonlane:Effect of Ethers
These 2 papers give some basic ideas of reaction types (reactionkinetique) some direct precipitation from "big" dianions.
2002_Leghie_Important comments on mechanism of electrochemical reduction of sulfur in DMF (and its "reply")
First step of S8 reduction is given (ring character vs. linear character). Cyclic voltammograms of Li2S8 + DMF and Li2S6 + DMF respectively are given. Read the original paper recommanded! Classical dianions + monoanions such as S3- and S4-. Coloured solution is also mentioned. Electrode type can influence the result (see "reply").
2001_Evans_The mecahnism for the cathodic reaction of sulfur in dimethylformamide:low temperature voltammetry
Method: cyclic voltammetry of sulfur in DMF. Paper mainly focuses on low temperature behaviour of Li-S. Mechanism at (even) 223 K is given and S8(4-) is a surprising result.
1997_Levillain_Polysulfides in dimethylformamide:only the redox couples Sn-Sn2- are involved and
1996_Levillain_On the understanding of the reduction of sulfur (S8) in dimethylformamide (DMF)
Using cyclic voltammetry, these paper show that the redox properties of Li2S6 + DMF solutions can be described by a relatively simple mechanism (one-electron transfers, dissociation, disproportionation and TSR reactions) and that it is not necessary to consider complex rearrangement reaction or transient species.