Reactivity and Interplay of Critical Components in Sodium-Ion Batteries

Diese Arbeit beleuchtet den Einfluss entscheidender Komponenten in Natrium-Ionen Batte-rien. Na-Metall wird häufig als Gegen- und/oder Referenzelektrode in der Literatur einge-setzt, um die Eigenschaften eines Aktivmaterials in Na-Ionen Batterien elektrochemisch zu untersuchen. Diese Thesis zeigt, dass Na spontan mit den häufig verwendeten, auf organi-schen Carbonaten basierten Elektrolyten reagiert. Solche Nebenreaktionen zwischen den Na-Gegen- und/oder Referenzelektroden führen zu veränderten Eigenschaften des Elektrolyten und wirken sich negativ auf die Oberflächenchemie der Arbeitselektrode aus. Eine Stabili-sierung des Na-Metalls kann durch Zugabe von Fluorethylencarbonat zu Carbonat-basierten Lösungsmitteln oder durch Ersetzen solcher Lösungsmittel durch Diglyme erfolgen. Der Einfluss dieser Lösungsmittel kann durch elektrochemische Messungen von Sb2O3-basierten Halbzellen bewertet werden. Die Zugabe von Fluorethylencarbonat führt zu einer geeigneten Dicke der Fest-Elektrolyt Interphase und verhindert, dass die Elektrode stark reißt. Diglyme dagegen löst Sb-Ionen während des Zyklierens, was zu Verunreinigungen, einem starken Kapazitätsverlust und einer unregelmäßigen elektrochemischen Signatur führt. Daher ist der Fluorethylencarbonat-haltige Elektrolyt für die Untersuchung von Materialien mit hoher Kapazität wie Sb am besten geeignet. Die Energiespeicherung von Sb durch Legierungsreak-tionen mit Na erfordert ein spezielles Elektrodendesign für eine hohe Leistungsstabilität. In dieser Arbeit wird systematisch der Einfluss der Kohlenstoffeigenschaften auf Sb/C-Verbundelektroden untersucht. Anstelle einer komplexen Hybridisierung von Sb und C wer-den die Komponenten mechanisch gemischt, um stabile Sb/C Elektroden zu erhalten. Dies ist nur unter Berücksichtigung der physikalischen, chemischen und strukturellen Merkmale der Kohlenstoffe möglich. Die beste Leistung wird nicht nur durch die hohe Oberfläche oder den Heteroatomgehalt ausgelöst, sondern insbesondere durch die beste Fähigkeit, sich ho-mogen zwischen den Sb Partikeln zu verteilen. Dies ist am besten für synthetisiertes Sb-Nanopulver mit Hilfe von Kohlenstoffzwiebeln möglich, die bei 1300 °C unter Vakuum her-gestellt werden. Durch Volumenänderungen verursachte Elektrodenrisse werden so verhin-dert und die Homogenität der Fest-Elektrolyt Interphase wird verbessert, was zu einer be-merkenswerten Ratenfähigkeit und einer hohen Zyklenstabilität führt. Um den Einfluss der Sb-Partikelgröße zu untersuchen, wird das synthetisierte Pulver durch kommerzielles Sb ersetzt, das vor der Elektrodenherstellung kugelgemahlen wird. Zusätzlich wird ein Sb/C Komposit aus kommerziellen Materialien durch Kugelmahlen hergestellt. Ein Vergleich aller Sb/C Elektroden zeigt, dass die Partikelgröße von Sb ein wesentlicher Faktor ist: Je kleiner die Partikel, desto höher die Zyklenstabilität und desto weniger Kohlenstoff wird zum Dämpfen von Volumenänderungen benötigt. Eine gründliche Anpassung der Sb- und C-Mengen und ihrer Merkmale ist erforderlich, um das bestmögliche elektrochemische Ver-halten zu erzielen

Goodbye smokers' corner: Health effects of school smoking bans

We estimate the causal impact of school smoking bans in Germany on the propensity and intensity of smoking. Using representative longitudinal data, we use variation in state, year, age cohort, school track, and survey time for implementation of such smoking bans to identify the effects of interest. The estimates from our multipledifferences approach show that six to ten years after intervention, propensity towards smoking is reduced by 7-16 percent, while the number of smoked cigarettes per day decreases by 8-13 percent. Our results still hold if we account for the clustered data structure by evaluating the effects with randomization inference.Wir untersuchen die kausalen Auswirkungen des Rauchverbots an Schulen in Deutschland auf die Wahrscheinlichkeit zu rauchen und die Anzahl gerauchter Zigaretten pro Tag. Um diese Effekte zu messen, verwenden wir einen repräsentativen Paneldatensatz und nutzen Variationen zwischen Bundesländern, Jahren, Alterskohorten, Schulformen und Interviewzeitpunkten in Bezug auf das Inkrafttreten der Intervention. Die Schätzungen unseres multiplen Differenzenansatzes zeigen, dass sich sechs bis zehn Jahre nach Einführung der Verbote an Schulen die Wahrscheinlichkeit zu rauchen um 7-17 Prozent reduziert, während die Anzahl an gerauchten Zigaretten pro Tag um 8-13 Prozent sinkt. Unsere Ergebnisse bleiben auch dann robust, wenn wir der Clusterstruktur der Daten Rechnung tragen und die Effekte mit Randomisierungsinferenz evaluieren

Effect of Continuous Capacity Rising Performed by FeS/Fe₃C/C Composite Electrodes for Lithium‐Ion Batteries

FeS‐based composites are sustainable conversion electrode materials for lithium‐ion batteries, combining features like low cost, environmental friendliness, and high capacities. However, they suffer from fast capacity decay and low electron conductivity. Herein, novel insights into a surprising phenomenon of this material are provided. A FeS/Fe3C/C nanocomposite synthesized by a facile hydrothermal method is compared with pure FeS. When applied as anode materials for lithium‐ion batteries, these two types of materials show different capacity evolution upon cycling. Surprisingly, the composite delivers a continuous increase in capacity instead of the expected capacity fading. This unique behavior is triggered by a catalyzing effect of Fe3C nanoparticles. The Fe3C phase is a beneficial byproduct of the synthesis and was not intentionally obtained. To further understand the effect of interconnected carbon balls on FeS‐based electrodes, complementary analytic techniques are used. Ex situ X‐ray radiation diffraction and ex situ scanning electron microscopy are employed to track phase fraction and morphology structure. In addition, the electrochemical kinetics and resistance are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. These results reveal that the interconnected carbon balls have a profound influence on the properties of FeS‐based electrodes resulting in an increased electrode conductivity, reduced particle size, and maintenance of the structure integrity

Lorentz meets Fano spectral line shapes: A universal phase and its laser control

Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures that quantify the structural and dynamical properties of nuclei, atoms, molecules, and solids. This study introduces a universal temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase {\phi} of the time-dependent dipole-response function. The formalism is confirmed experimentally by laser-transforming Fano absorption lines of autoionizing helium into Lorentzian lines after attosecond-pulsed excitation. We also prove the inverse, the transformation of a naturally Lorentzian line into a Fano profile. A further application of this formalism amplifies resonantly interacting extreme-ultraviolet light by quantum-phase control. The quantum phase of excited states and its response to interactions can thus be extracted from line-shape analysis, with scientific applications in many branches of spectroscopy.Comment: 11 pages, 4 figure

Functionalization of Graphite Electrodes with Aryl Diazonium Salts for Lithium‐Ion Batteries

The functionalization of electrode surfaces is a useful approach to gain a better understanding of solid–electrolyte interphase formation and battery performance in lithium-ion batteries (LIBs). Electrografting and deprotection of alkyl silyl protected ethynyl aryl diazonium salts on graphite electrodes were performed. Furthermore, electrografting of aryl diazonium salts carrying functional groups such as amino, carboxy and nitro, and their influence on the electrochemical performance in LIBs were investigated. The drawbacks of electrografted and especially deprotected samples were evaluated and compared to corresponding in situ grafted samples. While electrografted samples tend to lower the delithiation capacities, in situ grafted samples, except amino groups, reveal higher capacities. Ethynyl (TMS) shows improved capacities at 1 C and better capacity retention compared to the pristine graphite electrode. Additionally, the Coulombic efficiency of the first cycle was enhanced for in situ grafted samples

Glyoxylic acetals as electrolytes for Si/Graphite anodes in lithium-ion batteries

Using silicon-containing anodes in lithium-ion batteries is mainly impeded by undesired side reactions at the electrode/electrolyte interface leading to the gradual loss of active lithium. Therefore, electrolyte formulations are needed, which form a solid electrolyte interphase (SEI) that can accommodate to the volume changes of the silicon particles. In this work, we analyze the influence of two glyoxylic acetals on the cycling stability of silicon-containing graphite anodes, namely TMG (1 M LiTFSI in 1,1,2,2-tetramethoxyethane) and TEG (1 M LiTFSI in 1,1,2,2-tetraethoxyethane). The choice of these two electrolyte formulations was motivated by their positive impact on the thermal stability of LIBs. We investigate solid electrolyte decomposition products employing x-ray photoelectron spectroscopy (XPS). The cycling stability of Si/Gr anodes in each electrolyte is correlated to changes in SEI thickness, composition, and morphology upon formation and aging. This evaluation is completed by comparing the performance of TMG and TEG to two carbonate-based reference electrolytes (1 M LiTFSI in 1:1 ethylene carbonate: dimethyl carbonate and 1 M LiPF6 in the same solvent mixture). Cells cycled in TMG display inferior electrochemical performance to the two reference electrolytes. By contrast, cells cycled in TEG exhibit the best capacity retention with overall higher capacities. We can correlate this to better film-forming properties of the TEG solvent as it forms a smoother and more interconnected SEI, which can better adapt to the volume changes of the silicon. Therefore, TEG appears to be a promising electrolyte solvent for silicon-containing anodes

Probing the Effect of Titanium Substitution on the Sodium Storage in Na₃Ni₂BiO₆ Honeycomb-Type Structure

Na$_{3}$Ni$_{2}$BiO$_{6}$ with Honeycomb structure suffers from poor cycle stability when applied as cathode material for sodium-ion batteries. Herein, the strategy to improve the stability is to substitute Ni and Bi with inactive Ti. Monoclinic Na$_{3}$Ni$_{2-x}$Bi$_{1-y}$Ti$_{x+y}$O$_{6}$ powders with different Ti content were successfully synthesized via sol gel method, and 0.3 mol of Ti was determined as a maximum concentration to obtain a phase-pure compound. A solid-solution in the system of O3-NaNi$_{0.5}$Ti$_{0.5}$O$_{2}$ and O3-Na$_{3}$Ni$_{2}$BiO$_{6}$ is obtained when this critical concentration is not exceeded. The capacity of the first desodiation process at 0.1 C of Na$_{3}$Ni$_{2}$BiO$_{6}$ (~93 mAh g$^{-1}$) decreases with the increasing Ti concentration to ~77 mAh g$^{-1}$ for Na$_{3}$Ni$_{2}$Bi$_{0.9}$Ti$_{0.1}$O$_{6}$ and to ~82 mAh g$^{-1}$ for Na$_{3}$Ni$_{Zahl0.9}$Bi$_{0.8}$Ti$_{0.3}$O$_{6}$, respectively. After 100 cycles at 1 C, a better electrochemical kinetics is obtained for the Ti-containing structures, where a fast diffusion effect of Na$^{+}$-ions is more pronounced. As a result of in operando synchrotron radiation diffraction, during the first sodiation (O1-P3-O’3-O3) the O’3 phase, which is formed in the Na$_{3}$Ni$_{2}$BiO$_{6}$ is fully or partly replaced by P’3 phase in the Ti substituted compounds. This leads to an improvement in the kinetics of the electrochemical process. The pathway through prismatic sites of Na$^{+}$-ions in the P’3 phase seems to be more favourable than through octahedral sites of O’3 phase. Additionally, at high potential, a partial suppression of the reversible phase transition P3-O1-P3 is revealed

The Interaction Between Electrolytes and Sb2O3–based Electrodes in Sodium Batteries: Uncovering Detrimental Effects of Diglyme

Conversion materials are promising to improve the energy density of sodium‐ion‐batteries (NIB). Nevertheless, they suffer from the drawback of phase transitions and pronounced volume changes during cycling, which causes cell instability. When using these types of electrodes, all cell‐components have to be adjusted. In this study, a tremendous influence of the electrolyte solution on Sb$_{2}$O$_{3}$ conversion electrodes for NIBs is discussed. Solutions based on three solvents and solvent combinations established for NIBs, ethylene carbonate/dimethyl carbonate (EC/DMC), EC/DMC+5 % fluoroethylene carbonate (FEC), and diglyme, lead to a massively divergent electrochemical behavior of the same Sb$_{2}$O$_{3}$ electrode. Sb$_{2}$O$_{3}$ demonstrates the highest stability in solutions containing FEC, because this component forms a flexible, protecting surface film that prevent disintegration. One key finding of this work is that electrolyte solutions based on ether solvents like diglyme can remove Sb‐ions from Sb$_{2}$O$_{3}$ during cycling. Diglyme has the ability to coordinate and extract Sb$^{3+}$ during the oxidation of Sb$_{2}$O$_{3}$. This leads to contaminations of all cell components and a strong capacity loss together with an irregular electrochemical signature. Due to its poor reactivity at low potentials, diglyme forms a thin or even no surface layer. Thereby, there are no protecting films on the Sb$_{2}$O$_{3}$ electrodes that can avoid Sb$^{3+}$ ion dissolution. A critical examination of the electrolyte solutions components’ impact is essential to match them with conversion reaction anodes

Choosing the right carbon additive is of vital importance for high-performance Sb-based Na-ion batteries

Electrodes based on alloying reactions for sodium-ion batteries (NIB) offer high specific capacity but require bespoken electrode material design to enable high performance stability. This work addresses that issue by systematically exploring the impact of carbon properties on antimony/carbon composite electrodes for NIBs. Since the Sb surface is covered by an insulating oxide layer, carbon additives are crucial for the percolation and electrochemical activity of Sb based anodes. Instead of using complex hybridization strategies, the ability of mechanical mixing to yield stable high-performance Sb/C sodium-ion battery (NIB) electrodes is shown. This is only possible by considering the physical, chemical, and structural features of the carbon phase. A comparison of carbon nanohorns, onion-like carbon, carbon black, and graphite as conductive additives is given in this work. The best performance is not triggered by the highest or lowest surface area, and not by highest or lowest heteroatom content, but by the best ability to homogenously distribute within the Sb matrix. The latter provides an optimum interaction between carbon and Sb and is best enabled by onion-like carbon. A remarkable rate performance is attained, electrode cracking caused by volume expansion is successfully prevented, and the homogeneity of the solid/electrolyte interphase is significantly improved as a result of it. With this composite electrode, a reversible capacity of 490 mA h g-1 at 0.1 A g-1 and even 300 mA g-1 at 8 A g-1 is obtained. Additionally, high stability with a capacity retention of 73% over 100 cycles is achieved at charge/discharge rates of 0.2 A g-1 This journal is © The Royal Society of Chemistry