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Operando (micro) XAFS analysis
Katarina Vogel-Mikuš, Robert Dominko, Iztok Arčon, 2016, published scientific conference contribution abstract (invited lecture)

Abstract: In the talk the principles of XAS methods were presented with practical examples which illustrate the possibilities and advanced approaches for their use in structural analysis of different types of materials. The emphasis will be on to the use of XAS spectroscopy in operando mode and in combination with X-ray microscopy.
Found in: osebi
Keywords: X-ray absorption spectroscopy, X-ray microscopy, EXAFS, XANES, opearndo mode
Published: 25.03.2016; Views: 2553; Downloads: 47
.pdf Fulltext (18,40 MB)

Study of Li-S batteries by S K-edge RIXS spectroscopy
Robert Dominko, Iztok Arčon, Marko Petrič, Klemen Bučar, Matjaž Žitnik, Matjaž Kavčič, 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.
Found in: osebi
Keywords: RIXS, RXES, Li-S battery, operando, Sulphur K-edge XANES, Lithium polysulphides, Li2S
Published: 28.06.2016; Views: 2716; Downloads: 0
.pdf Fulltext (60,50 KB)

Operando characterization of batteries using x-ray absorption spectroscopy: advances at the beamline XAFS at synchrotron Elettra
Nicola Novello, Iztok Arčon, Lorenzo Stievano, Robert Dominko, marco Giorgetti, Giuliana Aquilanti, Luca Ivanc Olivieri, 2017, original scientific article

Abstract: X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on both local structure and electronic properties in a chemically selective manner. It can be used to characterize the dynamic processes that govern the electrochemical energy storage in batteries, and to shed light on the redox chemistry and changes in structure during galvanostatic cycling to design cathode materials with improved properties. Operando XAS studies have been performed at beamline XAFS at Elettra on different systems. For Li-ion batteries, a multiedge approach revealed the role of the different cathode components during the charge and discharge of the battery. In addition, Li-S batteries for automotive applications were studied. Operando sulfur K-edge XANES and EXAFS analysis was used to characterize the redox chemistry of sulfur, and to relate the electrochemical mechanism to its local structure.
Found in: osebi
Keywords: operando studies, x-ray absorption spectroscopy, Li-ion batteries, Li-S batteries
Published: 03.03.2017; Views: 3135; Downloads: 0
.pdf Fulltext (1,59 MB)

The mechanism of Li2S activation in lithium-sulfur batteries: Can we avoid the polysulfide formation?
Robert Dominko, Tim-Patric Fellinger, Markus Antonietti, Giuliana Aquilanti, Lorenzo Stievano, Iztok Arčon, Elena Tchernychova, Laurent Chabanne, Alen Vižintin, 2017, original scientific article

Abstract: Electrochemical reactions in the LieS batteries are considered as a multistep reaction process with at least 2e3 equilibrium states. Here we report a possibility of having a conversion of Li2S into sulfur without detectible formation of polysulfides. That was confirmed by using a novel material system consisting of carbon coated Li2S particles prepared by carbothermal reduction of Li2SO4. Two independent in operando measurements showed direct oxidation of Li2S into sulfur for this system, with almost negligible formation of polysulfides at potentials above 2.5 V vs. Li/Liþ. Our results link the diversity of first charge profiles in the literature to the Li2S oxidation mechanism and show the importance of ionic wiring within the material. Furthermore, we demonstrate that the Li2S oxidation mechanism depends on the relative amount of soluble sulfur in the electrolyte. By controlling the type and the amount of electrolyte within the encapsulating carbon shell, it is thereby possible to control the reaction mechanism of Li2S activation.
Found in: osebi
Keywords: Lithium-sulfur batteries Li2S active material XAS UV/Vis spectroscopy Li2S activation
Published: 03.03.2017; Views: 2224; Downloads: 0
.pdf Fulltext (2,98 MB)

A Mechanistic Study of Magnesium Sulfur Batteries
Ana Robba, Alen Vižintin, Jan Bitenc, Gregor Mali, Iztok Arčon, Matjaž Kavčič, Matjaž Žitnik, Klemen Bučar, Giuliana Aquilanti, Charlotte Martineau-Corcos, Anna Randon-Vitanova, Robert Dominko, 2017, original scientific article

Abstract: Magnesium sulfur batteries are considered as attractive energy storage devices due to the abundance of electrochemically active materials and high theoretical energy density. Here we report the mechanism of a Mg-S battery operation, which was studied in the presence of simple and commercially available salts dissolved in a mixture of glymes. The electrolyte offers high sulfur conversion into MgS in the first discharge with low polarization. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS and NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral environment resembling the wurtzite structure, while chemically synthesized MgS crystalizes in the rock-salt structure with octahedral coordination of magnesium.
Found in: osebi
Keywords: magnesium, sulfur, rechargeable batteries, XAS, NMR
Published: 19.10.2017; Views: 1426; Downloads: 0
.pdf Fulltext (1,48 MB)

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.
Found in: osebi
Keywords: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Published: 01.06.2018; Views: 920; Downloads: 0
.pdf Fulltext (579,89 KB)

Fluorinated ether based electrolyte for high-energy lithium-sulfur batteries
Robert Dominko, Patrik Johansson, Giuliana Aquilanti, Iztok Arčon, Klemen Pirnat, Alen Vižintin, Steffen Jeschke, Sara Drvarič Talian, 2018, published scientific conference contribution abstract

Found in: osebi
Keywords: Li-žveplive baterije, XANES, polisulfidi
Published: 12.09.2018; Views: 654; Downloads: 0
.pdf Fulltext (148,44 KB)

Sulfur based batteries studied by in-operando S K-edge RIXS and XAS spectroscopy
Matjaž Žitnik, Iztok Arčon, Alen Vižintin, Janez Bitenc, Ana Robba, Matjaž Kavčič, 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).
Found in: osebi
Keywords: Mg-Sulphur batteries, XANES, RIXS
Published: 13.09.2018; Views: 1067; Downloads: 0
.pdf Fulltext (123,32 KB)

Role of Cu current collector on electrochemical mechanism of Mg–S battery
Ana Robba, Maja Mežnar, Alen Vižintin, Jan Bitenc, Jernej Bobnar, Iztok Arčon, Anna Randon-Vitanova, Robert Dominko, 2020, original scientific article

Abstract: Development of magnesium sulfur battery is accompanied with all known difficulties present in Li–S batteries, however with even more limited choice of electrolytes. In the present work, the influence of current collector on electrochemical mechanism was investigated in light of different reports where improved behavior was ascribed to electrolyte. Notable differences in cycling behavior are reported when Al current collector is replaced by Cu current collector independent of electrolyte. The initial reduction of sulfur follows similar reaction path no mater of current collector, but formation of MgS can be in competition with formation of CuS in the presence of Cu cations. With the subsequent cycling cells prepared from cathodes deposited on Cu current collector show decrease in the voltage and formation of single plateau during cycling. The change corresponds to the involvement of Cu into the reaction and formation of redox couple Mg/CuS as determined by Cu K-edge XANES measurements. Corrosion of Cu foil is identified by SEM and serves as a source of Cu cations for the chemical reaction between Cu and polysulfides. Mg/CuS redox couple shows improved cycling stability, but theoretical energy density is severely reduced due to substitution of S with CuS as cathode active material.
Found in: osebi
Keywords: Magnesium Sulfur Rechargeable batteries Current collector Copper Corrosion
Published: 16.01.2020; Views: 333; Downloads: 0
.pdf Fulltext (1,86 MB)

Effects of a Mixed O/F Ligand in the Tavorite-Type LiVPO4O Structure
Sorour Semsari Parapari, Jean-Marcel Ateba Mba, Elena Tchernychova, Gregor Mali, Iztok Arčon, Gregor Kapun, Mehmet Ali Gülgün, Robert Dominko, 2020, original scientific article

Abstract: We report the synthesis and detailed structural and chemical characterization including electrochemical properties of a lithium vanadium oxy/fluoro-phosphate material. To the best of our knowledge, we have for the first time synthesized a LiVPO4O-type phase with a mixed O/F ligand. In the synthesis procedure, the LiVPO4O precursor compound was fluorinated via LiF incorporation, with preservation of the LiVPO4O framework structure. The operating potential of the synthesized material is increased compared to that of the LiVPO4O precursor (4.12 V vs 3.95 V versus metallic lithium, respectively). The related increase in operating potential was assigned to the effect of the intermixing O/F ligand, which is attained via the successful fluorine incorporation into the LiVPO4O structure. A characterization of the investigated materials was performed using microscale-covering XRD, XANES, and NMR techniques as well as nanoscale spatially resolved imaging and analytical STEM techniques. The obtained oxy/fluoro-phosphate phase is isostructural to LiVPO4O; however, the presence of the mixed O/F ligand promoted a higher symmetry of vanadium octahedra. These variations of the vanadium local environment along with the observed inhomogeneous distribution of the incorporated fluorine gave rise to the minor local deviations in vanadium valence. Our results clearly emphasize the connection among the fluorine ligand incorporation, its local distribution, and the electrochemical properties of the material.
Found in: osebi
Keywords: LiVPO4O, XRD, SEM, V XANES, Tavorite-Type, electrochemical properties
Published: 17.02.2020; Views: 315; Downloads: 0
.pdf Fulltext (3,11 MB)

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