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1.
A mechanistic study of metal sulfur batteries
Robert Dominko, Alen Vižintin, Sara Drvarič Talian, Ana Robba, Iztok Arčon, 2018, published scientific conference contribution abstract (invited lecture)

Keywords: Li-sulphur batteries, Sulphur XANES, magnesium
Published in RUNG: 15.10.2020; Views: 2313; Downloads: 0

2.
Sulfur based batteries studied by in-operando S K-edge RIXS and XAS spectroscopy
Matjaž Kavčič, Ana Robba, Janez Bitenc, Alen Vižintin, Iztok Arčon, Matjaž Žitnik, Klemen Bučar, Robert Dominko, 2018, published scientific conference contribution abstract

Abstract: Sulfur based batteries are considered as very attractive energy storage devices. Sulfur is one of the most abundant elements in the earth, it is electrochemically active material which can accept up to two electrons per atom. In combination with alkali metals, sulfur forms electrochemical couples with much higher theoretical energy density compared to Li-ion batteries commonly available today. At the moment, the electrochemical couple with Li is most extensively studied. While the main principle of operation is known the relevant operation mechanism(s) is not completely clear. Even more promising is the electrochemical couple with Mg providing almost twofold higher volumetric energy density due to its ability to provide two electrons during oxidation. However, Mg-S batteries are still in the very early stage of research and development and the complex mechanism of sulfur conversion has been less extensively studied. In order to improve the understanding of sulfur electrochemical conversion and its interactions within electrode, we need to apply new experimental approaches capable to provide precise information about local environment of S in the cathode during battery operation. In our work, resonant inelastic X-ray scattering (RIXS) and XAS measurements at the sulfur K-edge performed in operando mode were used to study the lithium-polysulfide formation during the discharge process. Measurements were performed at ID26 beamline of the ESRF synchrotron using tender X-ray emission spectrometer [1]. Resonant excitation condition enhanced the sensitivity for the lithium−polysulfide detection. On the other hand, the sulfate signal from the electrolyte was heavily suppressed and the self-absorption effects minimized due to fixed excitation energy. This experimental methodology was used to provide quantitative analysis of sulfur compounds in the cathode of a Li−S battery cell during the discharge process [2]. The high-voltage plateau in the discharge curve was characterized by a rapid conversion of solid sulfur into liquid phase Li polysulfides reaching its maximum at the end of this plateau. At this point the starting point for the precipitation of the Li2S from the liquid polysulfide phase was observed. The same approach has been used also for the Mg-S battery revealing similar mechanism as in case of Li-S battery [3]. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and Mg polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau).
Keywords: Mg-Sulphur batteries, XANES, RIXS
Published in RUNG: 13.09.2018; Views: 4378; Downloads: 0
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3.
Polysulfides formation in different electrolytes from the perspective of X-ray absorption spectroscopy
Robert Dominko, Alen Vižintin, Giuliana Aquilanti, Lorenzo Stievano, Maria Joseph Helen, Anji Reddy Munnangi, Maximilian Fichtner, Iztok Arčon, 2018, original scientific article

Abstract: 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.
Keywords: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Published in RUNG: 01.06.2018; Views: 3501; Downloads: 0
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4.
Study of Li-S batteries by S K-edge RIXS spectroscopy
Matjaž Kavčič, Matjaž Žitnik, Klemen Bučar, Marko Petrič, Iztok Arčon, Robert Dominko, Alen Vižintin, 2016, published scientific conference contribution abstract

Abstract: Li-S batteries are considered as one of the most promising candidates for future batteries in applications where high energy density is required [1]. Despite that the general principle of operation is known for a long time [2], the lack of detailed understanding of relevant operation mechanisms has so far prevented their extensive use. A Li-S battery is composed of a lithium metal anode and a sulfur based cathode, separated by a porous separator wetted with electrolyte. During the battery cycle the reduction and oxidation of S to Li2S and back proceeds through a complicated equilibrium mixture of compounds that are typically dissolved in the electrolyte in the form of long and short chain polysulfides. In order to improve our understanding of polysulfide formation and its interactions within electrode, which are essential to achieve the long term cycling stability, development and application of new analytical tools is required. In this work sulfur K-edge resonant X-ray emission (RXES) measurements were performed on the Li-S battery in operando mode. The experiment was performed at the ID26 beamline at ESRF using the Johansson type tender x-ray emission spectrometer [3]. Full K-L RIXS maps were recorded on a set of chemically prepared Li2Sx sample standards characterized by different Li:S stoichiometric ratio, followed by the operando measurements on Li-S battery. Using the spectra recorded on Li2Sx standards two excitation energies were chosen and RXES spectra from the back of the battery cathode were sequentially acquired during one discharge cycle (C20). The relative amounts of each sulfur compound in the cathode during the discharge cycle were determined from the linear combination fit using measured reference standard spectra. Because of resonant excitation conditions the sensitivity for the polysulfide detection was significantly enhanced. Our work sets up S K-edge RIXS spectroscopy as an important analytical tool to study the mechanism of Li-polysulfide formation in the cathode and their interaction with the host matrix and electrolyte.
Keywords: RIXS, RXES, Li-S battery, operando, Sulphur K-edge XANES, Lithium polysulphides, Li2S
Published in RUNG: 28.06.2016; Views: 5580; Downloads: 0
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