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1.
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, izvirni znanstveni članek

Opis: 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.
Najdeno v: osebi
Ključne besede: operando studies, x-ray absorption spectroscopy, Li-ion batteries, Li-S batteries
Objavljeno: 03.03.2017; Ogledov: 3063; Prenosov: 0
.pdf Polno besedilo (1,59 MB)

2.
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, izvirni znanstveni članek

Opis: 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.
Najdeno v: osebi
Ključne besede: Lithium-sulfur batteries Li2S active material XAS UV/Vis spectroscopy Li2S activation
Objavljeno: 03.03.2017; Ogledov: 2147; Prenosov: 0
.pdf Polno besedilo (2,98 MB)

3.
Edge profiles in K shell photoabsorption spectra of gaseous hydrides of 3p elements and homologues
Giuliana Aquilanti, Alojz Kodre, Iztok Arčon, Robert Hauko, Jana Padežnik Gomilšek, izvirni znanstveni članek

Opis: Photoabsorption spectra of gaseous hydrides of 3p elements (PH3, H2S, HCl) are measured in the energy region of photoexcitations pertaining to K edge. The analysis of the edge profile is extended to hydrides of 4p series (GeH4, AsH3, H2Se, HBr) from an earlier experiment, and to published spectra of 2p hydrides (CH4, NH3, H2O, HF) and noble gases Ar, Kr and Ne and SiH4. The edge profiles are modelled with a linear combination of lorentzian components, describing excitations to individual bound states and to continuum. Transition energies and probabilities are also calculated in the non-relativistic molecular model of the ORCA code, in good agreement with the experiment. Edge profiles in the heavier homologues are closely similar, the symmetry of the molecule governs the transitions to the lowest unoccupied orbitals. In 2p series the effect of the strong nuclear potential prevails. Transitions to higher, atomic-like levels remain very much the same as in free atoms.
Najdeno v: osebi
Ključne besede: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT
Objavljeno: 23.08.2017; Ogledov: 1109; Prenosov: 0
.pdf Polno besedilo (703,57 KB)

4.
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, izvirni znanstveni članek

Opis: 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.
Najdeno v: osebi
Ključne besede: magnesium, sulfur, rechargeable batteries, XAS, NMR
Objavljeno: 19.10.2017; Ogledov: 1349; Prenosov: 0
.pdf Polno besedilo (1,48 MB)

5.
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, izvirni znanstveni članek

Opis: 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.
Najdeno v: osebi
Ključne besede: Li-S batteries, operando sulphur K-edge XANES, EXAFS, Li-polysulphides
Objavljeno: 01.06.2018; Ogledov: 849; Prenosov: 0
.pdf Polno besedilo (579,89 KB)

6.
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, objavljeni povzetek znanstvenega prispevka na konferenci

Najdeno v: osebi
Ključne besede: Li-žveplive baterije, XANES, polisulfidi
Objavljeno: 12.09.2018; Ogledov: 599; Prenosov: 0
.pdf Polno besedilo (148,44 KB)

7.
K-edge absorption spectra of gaseous hydrides
Iztok Arčon, Jana Padežnik Gomilšek, Robert Hauko, Alojz Kodre, Giuliana Aquilanti, 2018, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: X-ray absorption spectra in the energy region of absorption edges reveal fine details of the mechanism of inner-shell photoexcitation: in particular in spectra of free atoms or simple molecules, the simplest being gaseous hydrides [1-2]. In a collection of data from consecutive and homologous elements, analyzed by a common procedure, the reaction channels can be identified with better precision and reliability than in analysis of individual spectra. Absorption spectra of the hydrides of 3p elements (PH3, H2S in HCl) were measured at the XAFS beamline of the Elettra synchrotron in Trieste: a new type of adjustable absorption cell for measurement of noxious gases at room temperature and at low photon energies was developed for the purpose. For the analysis, data from an earlier experiment on 4p hydrides (GeH4, AsH3, H2Se, HBr), and published data of 2p hydrides (CH4, NH3, H2O, HF) [3-4] as well as SiH4 and the noble gases concluding the isoelectronic series (Ne, Ar, Kr) were adopted. The spectra are compared to respective calculated spectra, obtained by atomic HF86, GRASP codes and molecular DFT (Density functional theory) ORCA code [5]. Our analysis of the pre-edge structures showed that the energies and probabilities of singleelectron transitions into the lowermost orbitals with the molecular character were strongly affected by the symmetry of the molecule, essentially in the same way in 3p and 4p homologues, but not in 2p homologues with a stronger influence of the core charge. In transitions to higher orbitals with prevailing atomic character the influence of the molecular field is negligible. The fine structure immediately above the K edge stems from the coexcitation of valence electrons. These coexcitations can be explained as a two-step process: the inner-shell photoeffect followed by the shake-up of a valence electron predominantly to a free atomic orbital. The process is markedly different from coexcitations of more tightly bound electrons [3]. The results of relative shake-up probabilities can be compared to results of emission spectroscopies, the probabilities of double excitation to bound states show a correlation with the dissociation probability of the molecule.
Najdeno v: osebi
Ključne besede: večelektronske vzbuditve, hidridi, rentgenska absorpcijska spektroskopija
Objavljeno: 12.09.2018; Ogledov: 880; Prenosov: 0
.pdf Polno besedilo (88,18 KB)

8.
K-edge absorption spectra of isoelectronic gaseous hydrides: a combination of atomic and molecular channels
Alojz Kodre, Jana Padežnik Gomilšek, Robert Hauko, Iztok Arčon, Giuliana Aquilanti, 2018, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: The fine detail in the x-ray absorption spectra in the energy region of absorption edges provides the insight into the mechanism of inner-shell photoexcitation: in particular in spectra of free atoms or simple molecules, the simplest being gaseous hydrides [1-2]. Measured K edge absorption spectra of hydrides of 3p (PH3, H2S in HCl) and 4p (GeH4, AsH3, H2Se, HBr) elements, and published data of 2p hydrides (CH4, NH3, H2O, HF) as well as SiH4 [3-6] and the noble gases at the end of the isoelectronic series (Ne, Ar, Kr) are compared to the respective calculated spectra, obtained by atomic HF86, GRASP codes [7] and molecular DFT (Density functional theory) ORCA code [8]. For a clearer view of intraatomic processes, the weak and simple structural (XAFS) signal of the molecule is removed from the spectra. Among the spectral features below the continuum limit, those with the lowest energy belong to the transition of the core electron to the lowermost free orbitals with the molecular character. They are, as a rule, wider than the transitions to the higher orbitals with prevailing atomic character. The theoretical description with DFT code without specific adaptations is sufficient for a qualitative picture of the pre-edge structure. The fine structure immediately above the K edge stems from the coexcitation of valence electrons. We have proved that the coexcitations can be explained as a two-step process: the inner-shell photoeffect followed by the shake-up of a valence electron predominantly to a free atomic orbital. This process is markedly different from coexcitations of more tightly bound electrons [9]. In the collection of consecutive and homologous data, analyzed by a common procedure, the reaction channels can be identified with better precision and reliability than in analysis of individual spectra. Our analysis showed that the energies and probabilities of single-electron transitions into the molecular orbitals are strongly affected by the symmetry of the molecule, essentially in the same way in 3p and 4p homologues, but not in 2p homologues with a stronger influence of the core charge. In transitions to atomic orbitals the influence of the molecular field is negligible.
Najdeno v: osebi
Ključne besede: hidridi, rentgenska spektroskopija, XAFS
Objavljeno: 12.09.2018; Ogledov: 803; Prenosov: 0
.pdf Polno besedilo (63,16 KB)

9.
Effects of the molecular potential on coexcitations of valence electrons in the K-shell photoeffect of 3p and 4p elements
Robert Hauko, Jana Padežnik Gomilšek, Alojz Kodre, Iztok Arčon, Giuliana Aquilanti, 2019, izvirni znanstveni članek

Opis: Photoabsorption spectra of gaseous hydrides of 3p (PH3, H2S, HCl) and 4p elements (GeH4, AsH3 , H2Se, HBr) are measured in the energy region within 50 eV above the K edge, to study coexcitations of valence electrons by photoeffect in the K shell. The analysis of the valence coexcitations is extended to Ar, Kr, and SiH4. Relative probabilities and energies of states in the individual coexcitation channels are recovered by modeling the spectral features with a minimal ansatz based on the features in the contiguous noble gas. The extracted parameters are compared to the results of theoretical calculations for molecules (ORCA code) and free atoms (Hartree-Fock code). The experimental results confirm that the valence coexcitations in the 3p and 4p hydride molecules can be satisfactorily described by a two-step process, with the shake of the outer electron following the excitation of the core electron. The total probability—relative to the K-edge jump—of the shake-up processes shows a steady decrease from 19% in Si to 14% in Cl, and from 15% in Ge to 12% in Br. The experimental values for Ar (12%) and Kr (10%) are in accord with the trend. The dominant contribution is the transition to quasiatomic orbitals, in contrast with the deeper coexcitation channels in hydride molecules where transition to molecular orbitals prevails.
Najdeno v: osebi
Ključne besede: X-ray absorption spectra, gaseous hydrides, 3p K-edge spectra, DFT
Objavljeno: 05.09.2019; Ogledov: 391; Prenosov: 0
.pdf Polno besedilo (926,96 KB)

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