1,543 research outputs found
Anthraquinone based redox-active polymers for organic batteries
No full textThe development of new materials for energy storage systems plays an increasingly important role to compensate the growing demand for portable and flexible electronics. Redox-active organic compounds, in particular polymers, represent promising materials featuring many advantages such as flexibility, light-weight and being environmental friendly. Moreover, organic redox-active polymers can be produced at low temperature procedures from renewable or recycled resources and can be processed utilizing efficient and low-cost techniques (e.g., printing techniques). Anthraquinone-based polymers represent promising redox-active materials for the application in organic batteries or solar-rechargeable electric energy storage systems. The redox potential of anthraquinones can be tailored to the desired potential by straightforward modification of the carbonyl groups to electron donating or accepting groups (i.e., 1,3-dithiol-2-ylidene, N-cyanoimine, N,N-dicyanomethylene and thione group). Furthermore, a good charge-to-mass ratio is obtained due to the two electrons redox behavior, which results in comparably high theoretical capacities from 132 to 207 mAh/g. The introduction of low molar mass polymerizable groups, such as vinyl or ethynyl results in anthraquinone monomers that can be polymerized by straightforward polymerization techniques like free radical and rhodium-catalyzed polymerization, respectively. Lithium-organic batteries using the developed polymers as cathode material show promising charge/discharge behaviors with good cycling stability. The present results contribute to the understanding of the relationship between structure and electrochemical behavior and show new perspectives for the development of polymers with tailor-made redox potentials for novel redox-active materials in organic electronics
Untersuchungen von Natrium-Festkörperbatterien mit Schwerpunkt auf der Katholyt|Aktivmaterial-Grenzfläche in Kathodenkompositen
No full textAddressing the growing demand for energy storage of renewable energies involves exploring alternatives to lithium-ion batteries. Sodium-based battery materials have gained momentum in research as they offer similar cell chemistry. Additionally, sodium, iron and manganese used in sodium-based cells are more sustainable and cost-effective compared to the classical elements used in high-capacity lithium cells, such as lithium, cobalt and nickel. Despite the higher reac-tivity of sodium with water, sodium-ion batteries show better safety characteristics. However, they face the drawback of lower energy density compared to lithium counterparts.
To optimise the lower energy density issue, the use of solid electrolytes is being investigated not only in academia but in industry as well. Research on lithium-based systems has already shown an increase in energy density of solid-state batteries by employing anode materials with higher specific capacity, like lithium metal, compared to graphite. Solid-state batteries, in addition to their higher energy density, provide enhanced safety due to the non-flammable nature of solid electrolytes, as opposed to liquid electrolytes. Key challenges of solid-state cells include highly resistive interfaces, contact loss due to volume expansion and contraction of the electrodes, re-quiring compensation with high pressures, and interface reactions.
Transitioning from lithium to sodium and liquid to solid electrolyte requires careful considera-tion of the following aspects. Notably, graphite is not an efficient intercalation material for sodi-um, as sodium-ions do not form stable graphite intercalation compounds due to the size mis-match between sodium and the graphite interlayer spacing. More precisely, the increasing size and at the same time an insufficient chemical bonding between the alkali metal ion and the car-bon atoms lead to a positive formation energy. Therefore, either hard carbons, where sodium fills the pores, or elemental sodium is used in sodium-ion batteries. While liquid electrolytes are permeable to dendrites, sodium metal is primarily used as anode material for solid-state cells, along with alloy materials. Hard carbons have been introduced in solid-state cells but encounter challenges in establishing proper contact with the solid electrolyte. Different classes of separator electrolytes for sodium solid-state batteries are under study, each with distinct beneficial proper-ties such as good processability, high ionic conductivity or chemical stability. Cathodes of solid-state batteries are primarily composites of a redox active material with another ion- and often electron-conducting phase, being a solid electrolyte and carbon.
This study focuses on sodium-based all-solid-state battery systems, examining the influence of different electrolytes as separators or catholytes. Cathode composites with sulfide and halide catholytes where prepared, optimized and analyzed. Their cycling performance and especially the reaction with transition metal oxides was studied. Despite the lower ionic conductivity of the halide catholyte, its higher redox stability allowed cell cycling that was not possible with the sul-fide-based electrolyte. Regarding separator electrolytes, sulfides with and without doping were studied, and the need of a protective layer at the anode was determined. This protective layer, represented by an oxide ceramic electrolyte, exhibited beneficial stability at the anode but lacks the necessary flexibility to accommodate pressure changes in the cathode composite. Various methods, including time-of-flight secondary ion mass spectrometry, X-ray photoelectron spec-troscopy, electrochemical impedance spectroscopy, scanning electron microscopy and different cycling procedures, were employed to study these phenomena.
Overall, this thesis provides a detailed insight into current challenges in sodium all-solid-state full cells using halide, sulfide and oxide electrolytes. Based on this knowledge clear trends could be determined for future research approaches and optimization procedures. If the favorable sul-fide electrolytes are to be used as catholytes, coatings need to be introduced to protect the sul-fides from decomposition. The use of the halide with increased chemical stability necessitates an increase of ionic conductivity to ensure the ability to use higher currents. The anode|separator interface has to be improved, potentially by an alternative electrode material such as hard carbon instead of the sodium–tin alloy. The reason is the strong reactivity of the sulfide separator with both sodium metal and the alloy. If oxides may potentially be used, further investigations are needed regarding the mechanical challenges.Federal Ministry of Education and Research (BMBF
Graphite as co-intercalation host for sodium ion batteries
No full textThis cumulative Ph.D. thesis summarizes the research progress obtained during the last years on the role of graphite (and related anode materials) in SIBs. The study focus is on better understanding the co-intercalation reaction and to further improve the performance by changing electrochemical parameters, test environment, solvent and salt. This Ph.D. thesis is divided into two major parts. In the first part, a brief literature overview on the current state of research and the aim of this thesis are presented. In the second part, the summary of the scientific results that have been achieved and published in 3 articles and one submitted manuscript, is stated. ...Diese kumulative Doktorarbeit fasst die in den letzten Jahren erzielten Forschungsfortschritte zur Rolle von Graphit (und verwandten Anodenmaterialien) in SIBs zusammen. Der Schwerpunkt der Studie liegt auf einem besseren Verständnis der Kointerkalationsreaktion und darauf, die Speichereigenschaften weiter zu verbessern indem elektrochemische Parameter, die Testumgebung, Lösungsmittel und Salze verändert werden.
Diese Dissertation gliedert sich in zwei Hauptteile. Im ersten Teil wird ein kurzer Literaturüberblick über den aktuellen Forschungsstand und das Ziel dieser Arbeit gegeben. Im zweiten Teil wird die Zusammenfassung der wissenschaftlichen Ergebnisse, die in drei wissenschaftlichen Artikeln und einem eingereichten Manuskript erzielt und veröffentlicht wurden, gegeben
Medium-temperature solid-state batteries based on sodium-beta alumina
No full textThe demand for more powerful and cost-effective electrochemical energy storage systems is increasing. One focus is research into so-called "post-Li-ion" batteries, which are not based on lithium but on other alkali or alkaline earth metals, such as potassium or calcium. Another prominent approach is using sodium, e.g., as a negative electrode (hereafter: anode), in combination with a solid electrolyte, resulting in solid-state sodium cells. The ceramic, polycrystalline sodium-beta alumina solid electrolyte (BASE) might be a viable candidate due to its outstanding electrochemical properties, low cost, and abundant raw materials. As positive electrodes, intercalation-type positive electrodes might be viable. These are already used successfully in Li-ion systems. Notwithstanding, there is barely any research about combining these material combinations to a cell systems operating below 100 °C yet (δm, Na = 97.7 °C). This thesis gives attention to this fact. The project focuses on clarifying the requirements for and the construction of cells consisting of metallic sodium anodes, sodium-beta alumina, and Na-ion cathodes, which are operated at temperatures below 100 °C. The work highlights the challenges for this specific material combination, suggests possible compositions and instructions for action. It provides initial characteristic values for the system. In doing so all three core components of the cell, i.e., the anode, the cathode, and the solid electrolyte, and their interaction are considered. As the solid electrolyte is the core component of the cell system, three publications (Publication 1, Publication 2, Publication 3) are dedicated to this essential cell component. The interaction of anode and solid electrolyte is examined in Publications 2 and 4. Publications 4 and 5 show the combination of Na-ion cathodes with the solid electrolyte and investigate the resulting cell system
Generierung von aktiven Zentren auf Carbon Nanotubes für die oxidative Dehydrierung von Ethylbenzol
No full textDie Synthese von Styrol ist einer der zehn größten Herstellungsprozesse in der Petrochemie. Im Jahr 2010 wurden 25 Millionen Tonnen produziert, wobei die Nachfrage weiterhin steigt. Durch die Verwendung von Multiwalled Carbon Nanotubes als Katalysatoren (MWCNTs) und Zugabe von Sauerstoff zur Reaktionsmischung kann im Gegensatz zur industriell eingesetzten Dehydrierung von Ethylbenzol ein Vollumsatz thermodynamisch erreicht werden. Zusätzlich ist es möglich bei dieser oxidative Dehydrierung von Ethylbenzol die Reaktionstemperatur um 200 °C zu senken, ohne einen Verlust bei den Umsätzen hervorzurufen.
Innerhalb der Arbeit wurden verschiedene Methoden untersucht, mit denen die MWCNTs für den Einsatz als Katalysatoren verbessert werden konnten. Dabei wurden zum einen eine Erhöhung der Oberfläche durch KOH-Behandlung und zum anderen verschiedene Oxidationsverfahren an dem Kohlenstoffmaterial realisiert. Durch die Oxidationen wurden dabei die reaktiven Sauerstoffgruppen für die Katalyse im unterschiedlichen Mengen und Verhältnissen zueinander generiert. Die entstandenen aktiven Zentren wurden umfassend quantifiziert und daraus Reaktionsmechanismen für die Oxidationen an den MWCNTs abgeleitet.
Es zeigte sich bei dem Einsatz in der oxidativen Dehydrierung von Ethylbenzol, dass alle Sauerstoffgruppen auf den MWCNTs während der Reaktion zu den aktiven Zentren umgeformt werden und somit eine direkte Korrelation zwischen dem Funktionalisierungsgrad der MWCNTs und dem Umsatz von Ethylbenzol besteht. Eine Erhöhung der Oberfläche hingegen sorgte für eine geringere thermische Stabilität des Materials und führte zu einem Verlust des Katalysators innerhalb der ersten Stunden während der Katalyse
Exploration of Novel Cathode Active Materials for Sodium-Ion Batteries
No full textLithium-ion batteries (LIBs) have led the energy storage market for decades due to their excellent performance. However, the increasing scarcity and cost of lithium resources have shifted research interest toward alternative technologies. Sodium-ion batteries (SIBs), with their abundant sodium resources and competitive electrochemical properties, have emerged as promising candidates. In particular, O3-type layered oxide cathodes are attractive for practical applications due to their high sodium content and potential for high reversible capacity.
This dissertation focuses on optimizing Ni- and Mn-rich O3-type layered oxide cathodes for SIBs. Using NaNiO2 (NNO) as a prototype material, the work first addresses the challenges associated with irreversible phase transitions caused by Na+-de/intercalation-induced interlayer gliding and Jahn-Teller (JT) distortion from Ni3+. To improve the structural reversibility and electrochemical performance, Ti4+ was introduced to produce NaNi0.9Ti0.1O2 (NNTO), which was successfully synthesized via a solid-state reaction for the first time. NNTO exhibited a high specific capacity of 190 mAh/g, but suffered from chemo-mechanical degradation and irreversible lattice oxygen loss. To further address these limitations, Ca2+ was introduced as a pillaring ion. Among the various substitution levels explored, Na0.95Ca0.025Ni0.9Ti0.1O2 (CaNNTO) exhibited the largest interlayer spacing, along with best capacity retention and rate performance. In situ X-ray diffraction (XRD), scanning electron microscopy (SEM), acoustic emission (AE), and differential electrochemical mass spectrometry (DEMS) analyses confirmed that Ca2+ effectively mitigates interlayer gliding and volume collapse, thereby enhancing the reversibility of both nickel and oxygen redox reactions and increasing the structural and interfacial stability during electrochemical cycling.
The study was further extended to Mn-rich O3-type layered oxides. NaMnO2 (NMO), a cost-effective and environmentally friendly cathode candidate, is also known to undergo complex and irreversible phase transitions, along with significant manganese migration at high potentials. In this work, precipitated Mn3O4 was employed as a precursor for NMO synthesis. To enhance its structural and electrochemical properties, Ti4+ was introduced to form NaMn0.9Ti0.1O2 (NMTO). Titanium substitution effectively stabilized the O3 phase, suppressed the JT distortion associated with Mn3+, and facilitated the transformation from polycrystalline to quasi-single-crystalline morphology. The optimized NMTO also exhibited an enlarged interlayer spacing, enhanced capacity retention ([42-70] % after 50 cycles), and suppressed oxygen evolution, while effectively preventing the formation of the O1 phase, as confirmed by in situ XRD and DEMS measurements.
In conclusion, this dissertation demonstrates effective strategies for improving the structural and electrochemical stability of both Ni-rich and Mn-rich O3-type layered oxides. The mechanistic insights and material design principles presented herein provide valuable guidance for the development of high-performance sodium-ion cathode materials
The influence of transition metal addition on lithium stabilized Na-β″-alumina electrolytes
No full textThe present work elucidates the effects of 3d transition metal doping on ceramic, lithium stabilized Na-β″-alumina electrolytes. Three dopants, namely TiO2, Mn3O4, and NiO in various molar amounts, were analyzed for their effect on the synthesis and resulting properties of transition metal doped Na-β″-alumina electrolytes at three different sintering temperatures. The resulting electrolytes were characterized in respect of their phase content, sintering behavior, microstructure, characteristic fracture strength, and ionic conductivity. The work was complemented by introducing two battery application cases for doped Na-β″-alumina electrolytes
Philipp Melanchthon
No full textPhilipp Melanchthon (1497–1560) was, with Martin Luther, the most influential reformer of the church during the 16th century. He was also a reformer of university education, especially theological studies, as well as the school system in Germany. He was responsible for a theological curriculum that included Greek, Hebrew, and philosophy. He, as a professor of Greek at the University of Wittenberg since 1518, was the author of the first generally accepted Protestant confession, known as the Confessio Augustana (1530). He also wrote the first Protestant commentaries on Paul’s letter to the Romans (1519), as well as the first Protestant handbook in systematic theology (1521). He was the main negotiator of the Protestant movement during the diets and religious discussions with the Roman Catholic Church. He is known as the ‘teacher of Germany and Europe’ and is respected as the father of the ecumenical movement. Yet, Melanchthon is not known to South Africans and especially Afrikaans-speaking people who, traditionally, have close links with the reformational tradition. There is not yet one single publication on Melanchthon in Afrikaans or by a South African scholar, making this book, therefore, the first by an Afrikaans-speaking scholar on Melanchthon
#Bitcoin : an analysis of the field of a decentralized virtual currency using twitter data
No full textAuthor Philipp AllerstorferAbstract in englischer SpracheMasterarbeit Universität Linz 201
Chemisches und elektrochemisches Verhalten von Schwefel und Sulfiden in elektrochemischen Zellen
No full textThe cumulative dissertation is about different possibilities to use sulfur as part of electrochemical storage devices and is based on four independent publications. One is dealing with the mobility and identity of elemental sulfur in a porous carbon matrix. The property changes of sulfur which is staying in physical contact with carbon were monitored by different analytical methods and are discussed. The relevance of the findings regarding metal/sulfur-batteries was experimentally verified. The second topic was about the (electro)-chemical stability of the Li3PS4 solid electrolyte against lithium electrodes and InLi-alloy electrodes of different stoichiometry. The article discusses the relationship between electrode potential, electrode phase composition, and electrode/electrolyte-interface stability. Further, it provides a guideline for using InLi electrodes correctly in combination with thiophosphate solid electrolytes. The last project describes the realization of a Na/polysulfide-cell with two liquid electrolyte chambers separated by a solid electrolyte. Poor cyclability characteristics were counteracted with two approaches: The use of P2S5 as additive and tetramethylurea as solvent. Moreover, Vis-spectroscopy was applied and the tetramethylurea electrolyte has been characterized. A review article presenting the different concepts of sulfur utilization in electrochemical cells is also included. Therein, advantages, disadvantages, and challenges of the concepts are discussed. Besides the publications, the dissertation contains additional material. Among them, a review on low-temperature Na/S-batteries is given, detailed descriptions of electrochemical cell assemblies are provided, and relevant parameters towards electrochemical characterization methods are explained
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