Universität Stuttgart
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Item Open Access Binder-free V2O5 cathode for high energy density rechargeable aluminum-ion batteries(2020) Diem, Achim M.; Fenk, Bernhard; Bill, Joachim; Burghard, ZaklinaNowadays, research on electrochemical storage systems moves into the direction of post-lithium-ion batteries, such as aluminum-ion batteries, and the exploration of suitable materials for such batteries. Vanadium pentoxide (V2O5) is one of the most promising host materials for the intercalation of multivalent ions. Here, we report on the fabrication of a binder-free and self-supporting V2O5 micrometer-thick paper-like electrode material and its use as the cathode for rechargeable aluminum-ion batteries. The electrical conductivity of the cathode was significantly improved by a novel in-situ and self-limiting copper migration approach into the V2O5 structure. This process takes advantage of the dissolution of Cu by the ionic liquid-based electrolyte, as well as the presence of two different accommodation sites in the nanostructured V2O5 available for aluminum-ions and the migrated Cu. Furthermore, the advanced nanostructured cathode delivered a specific discharge capacity of up to ~170 mAh g-1 and the reversible intercalation of Al3+ for more than 500 cycles with a high Coulomb efficiency reaching nearly 100%. The binder-free concept results in an energy density of 74 Wh kg-1, which shows improved energy density in comparison to the so far published V2O5-based cathodes. Our results provide valuable insights for the future design and development of novel binder-free and self-supporting electrodes for rechargeable multivalent metal-ion batteries associating a high energy density, cycling stability, safety and low cost.Item Open Access Asymmetric Rh diene catalysis under confinement : isoxazole ring‐contraction in mesoporous solids(2024) Marshall, Max; Dilruba, Zarfishan; Beurer, Ann‐Katrin; Bieck, Kira; Emmerling, Sebastian; Markus, Felix; Vogler, Charlotte; Ziegler, Felix; Fuhrer, Marina; Liu, Sherri S. Y.; Kousik, Shravan R.; Frey, Wolfgang; Traa, Yvonne; Bruckner, Johanna R.; Plietker, Bernd; Buchmeiser, Michael R.; Ludwigs, Sabine; Naumann, Stefan; Atanasova, Petia; Lotsch, Bettina V.; Zens, Anna; Laschat, SabineCovalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.Item Open Access Cuttlebone-like V2O5 nanofibre scaffolds - advances in structuring cellular solids(2017) Knöller, Andrea; Runčevski, Tomče; Dinnebier, Robert E.; Bill, Joachim; Burghard, ZaklinaItem Open Access Towards recycling of LLZO solid electrolyte exemplarily performed on LFP/LLZO/LTO cells(2022) Ali Nowroozi, Mohammad; Iqbal Waidha, Aamir; Jacob, Martine; Aken, Peter A. van; Predel, Felicitas; Ensinger, Wolfgang; Clemens, OliverAll‐solid‐state lithium ion batteries (ASS‐LIBs) are promising due to their safety and higher energy density as compared to that of conventional LIBs. Over the next few decades, tremendous amounts of spent ASS‐LIBs will reach the end of their cycle life and would require recycling in order to address the waste management issue along with reduced exploitation of rare elements. So far, only very limited studies have been conducted on recycling of ASS‐LIBS. Herein, we investigate the recycling of the Li7La3Zr2O12 (LLZO) solid‐state electrolyte in a LiFePO4/LLZO/Li4Ti5O12 system using a hydrometallurgical approach. Our results show that different concentration of the leaching solutions can significantly influence the final product of the recycling process. However, it was possible to recover relatively pure La2O3 and ZrO2 to re‐synthesize the cubic LLZO phase, whose high purity was confirmed by XRD measurements.Item Open Access Insights into the first multi-transition-metal containing Ruddlesden-Popper-type cathode for all-solid-state fluoride ion batteries(2024) Vanita, Vanita; Waidha, Aamir Iqbal; Vasala, Sami; Puphal, Pascal; Schoch, Roland; Glatzel, Pieter; Bauer, Matthias; Clemens, OliverPromising cathode materials for fluoride-ion batteries (FIBs) are 3d transition metal containing oxides with Ruddlesden-Popper-type structure. So far, the multi-elemental compositions have not been investigated, but it could alternate the electrochemical performance similar to what has been found for cathode materials for lithium-ion batteries. In this study, we investigate RP type La2Ni0.75Co0.25O4.08 as an intercalation-based active cathode material for all-solid-state FIBs. We determine the structural changes of La2Ni0.75Co0.25O4.08 during fluoride intercalation/de-intercalation by ex situ X-ray diffraction, which showed that F- insertion leads to transformation of the parent phase to three different phases. Changes in the Ni and Co oxidation states and coordination environment were examined by X-ray absorption spectroscopy and magnetic measurements in order to understand the complex reaction behaviour of the phases in detail, showing that the two transition metals behave differently in the charging and discharging process. Under optimized operating conditions, a cycle life of 120 cycles at a critical cut-off capacity of 40 mA h g-1 against Pb/PbF2 was obtained, which is one of the highest observed for intercalation electrode materials in FIBs so far. The average coulombic efficiencies ranged from 85% to 90%. Thus, La2Ni0.75Co0.25O4.08 could be a promising candidate for cycling-stable high-energy cathode materials for all-solid-state FIBs.Item Open Access Optimizing the plasma oxidation of aluminum gate electrodes for ultrathin gate oxides in organic transistors(2021) Geiger, Michael; Hagel, Marion; Reindl, Thomas; Weis, Jürgen; Weitz, R. Thomas; Solodenko, Helena; Schmitz, Guido; Zschieschang, Ute; Klauk, Hagen; Acharya, RachanaA critical requirement for the application of organic thin-film transistors (TFTs) in mobile or wearable applications is low-voltage operation, which can be achieved by employing ultrathin, high-capacitance gate dielectrics. One option is a hybrid dielectric composed of a thin film of aluminum oxide and a molecular self-assembled monolayer in which the aluminum oxide is formed by exposure of the surface of the aluminum gate electrode to a radio-frequency-generated oxygen plasma. This work investigates how the properties of such dielectrics are affected by the plasma power and the duration of the plasma exposure. For various combinations of plasma power and duration, the thickness and the capacitance of the dielectrics, the leakage-current density through the dielectrics, and the current–voltage characteristics of organic TFTs in which these dielectrics serve as the gate insulator have been evaluated. The influence of the plasma parameters on the surface properties of the dielectrics, the thin-film morphology of the vacuum-deposited organic-semiconductor films, and the resulting TFT characteristics has also been investigated.Item Open Access Thermoanalytische und konstitutionelle Charakterisierung des Systems Si3N4-Y2O3-Al2O3-SiO2(2008) Ludwig, Thomas; Aldinger, Fritz (Prof. Dr.)Die gängigsten Additive für das Flüssigphasensintern von Si3N4 sind Y2O3 und Al2O3. Diese Oxide bilden mit dem immer auf der Oberfläche von Si3N4 befindlichen SiO2 eine flüssige Phase, die bei Temperaturen ab 1200°C Stickstoff löst. Nach der Abkühlung liegt ein Teil dieser Schmelzphase als amorphe stickstoffhaltige Korngrenzenphase vor, die in einer weiteren Wärmebehandlung teilweise auskristallisiert werden kann. Hierbei entstehen stickstoffhaltige Sekundärphasen wie zum Beispiel die Oxinitride Apatit, Y10(SiO4)6N2, Melilith, Y2Si3O3N4 und Wöhlerit Y4Si2O7N2. Da nur wenig thermodynamische Daten dieser oxinitridischen Phasen in der Literatur zu finden sind, wurden erstmals Wärmekapazitätsdaten auf direktem Wege mittels dynamischer Hochtemperaturkalorimetrie ermittelt. Im Fall von Apatit und Wöhlerit liegen die Messdaten bis 15% über der Neumann-Kopp-Abschätzungen, für Melilith 17% unterhalb der Abschätzung. Die Bildungsenthalpien der Verbindungen Yttrium-Monosilikat Y2SiO5, Ytterbium-Monosilikat (Yb2SiO5), YAM (Y4Al2O9), Apatit (Y10(SiO4)6N2) und Wöhlerit (Y4Al2O7N2) wurden mit Hochtemperatur-Einwurflösungskalorimetrie (Alkali-Borat-Schmelze als Lösungsmittel) gemessen. Die Verbindungen sind stabil bezüglich ihrer Ausgangsverbindungen und den Elementen. Eine Ausnahme liegt für die YAM Phase Y4Al2O9 vor. Die Bildungsenthalpie bezüglich den binären Oxiden ist nur schwach exotherm. Im System Y2O3-Al2O3-SiO2 wurde die eutektische Temperatur des SiO2-reichen Eutektikums überprüft und die Schmelzenthalpie bestimmt. Die eutektische Temperatur liegt mit 1371±5°C über den experimentellen Literaturwerten und unterhalb des von Gröbner [94Grö] berechneten Wertes. Desweiteren konnte eine quasiternäre Phase mit der Zusammensetzung Y0,9Al1,3Si1,7O7 (auf 7 Sauerstoff-Atome normiert) detektiert werden. Eine Strukturbestimmung war bisher nicht möglich. Auch ist nicht geklärt, ob die Phase nur metastabil vorliegt oder ob aus kinetischen Gründen die Bildung nur aus der Glasphase erfolgt. Geht man von der fremdionenstabilisierten y-Modifikation des Disilikats aus, so lässt sich die Stöchiometrie YAlSi2O7 als Endglied ableiten. Damit wäre auch die Elektroneutralitätsbedingung erfüllt. Es wurden Aluminosilikatgläser mit unterschiedlichem Stickstoffgehalt mit temperaturabhängiger Röntgenpulverdiffraktometrie untersucht, um die Kristallisation in situ zu verfolgen. Die Kristallisationstemperaturen nahmen mit steigendem Stickstoffgehalt zu. Dies ist auf die stärkere Vernetzung durch den Einbau des trivalenten Stickstoffanions zurückzuführen. Es erfolgt immer zuerst die Kristallisation einer Yttriumdisilikat-Modifikation, gefolgt von Aluminatphasen. Im Gegensatz zu Auslagerungsexperimenten kristallisiert das Disilikat in der für den entsprechenden Temperaturbereich stabilen Modifikation und wandelt dann mit zunehmender Temperatur in die nächst stabilere Modifikation um. Die Umwandlungstemperaturen stimmen mit den Literaturangaben überein. In klassischen Experimenten (Auslagerung eines Festkörpers im Ofen) findet meist zuerst eine Primärkristallisation zweier unterschiedlicher Disililikat-Modifikationen statt, wobei oft Modifikationen auskristallisieren, die bei den entsprechenden Temperaturen nicht stabil sein dürften. Da das Kristallisationsverhalten von der Beweglichkeit der Baugruppen oder Ionen im Glas abhängt und damit von der Viskosität, werden hier Strukturen bevorzugt die ähnlich der Struktureinheiten im Glas aufgebaut sind, obwohl sie thermodynamisch eigentlich nicht stabil sind.Item Open Access Realization of a classical Ruddlesden Popper type bilayer nickelate in Sr3Ni2-xAlxO7-δ with unusual Ni4+(2024) Yilmaz, Hasan; Küster, Kathrin; Starke, Ulrich; Clemens, Oliver; Isobe, Masahiko; Puphal, PascalThe discovery of 80 K superconductivity in bilayer La3Ni2O7 at pressures greater than 14 GPa presents a unique opportunity to study a novel class of high-temperature superconductors. Therefore, other bilayer nickelates following the classical (T4+) Ruddlesden-Popper (RP) series of Sr3Ni2O7 would present an interesting new candidate. In this work, we study the stabilization of RP n = 2 phase in Sr3Ni2-xAlxO7-δ, via floating zone growth of crystals. With powder and single-crystal XRD, we study the stability range of the RP-type phase. Our Thermogravimetric Analysis (TGA), X-ray photoelectron spectroscopy (XPS) and gas extraction studies reveal a remarkably high oxidation state of Ni4+ stabilized by chemical strain from Al. The obtained black crystals are insulating in transport and show a magnetic transition around 12 K.Item Open Access Towards recycling of all‐solid‐state batteries with argyrodite sulfide electrolytes : insights into electrolyte and electrode degradation in dissolution‐based separation processes(2025) Wissel, Kerstin; Hu, Zian; Wu, Xuebin; Jacob, Martine; Küster, Kathrin; Starke, Ulrich; Clemens, OliverAll‐solid‐state Li‐ion batteries (ASSBs) represent a promising leap forward in battery technology, rapidly advancing in development. Among the various solid electrolytes, argyrodite thiophosphates Li6PS5X (X=Cl, Br, I) stand out due to their high ionic conductivity, structural flexibility, and compatibility with a range of electrode materials, making them ideal candidates for efficient and scalable battery applications. However, despite significant performance advancements, the sustainability and recycling of ASSBs remain underexplored, posing a critical challenge for achieving efficient circular processes. This study investigates the dissolution‐based separation and recovery of argyrodite thiophosphate electrolytes and transition metal oxide electrode materials as a potential recycling strategy for ASSBs. A focus is set on the impact of solvent treatments on the recrystallization behavior of these electrolytes. Furthermore, the interactions between dissolved argyrodite thiophosphates and various transition metal oxide electrode materials (LiCoO2, LiMn2O4, LiNi0.8Mn0.1Co0.1O2, LiFePO4 and Li4Ti5O12) is examined to assess their influence on the functional properties of both the electrolytes and electrode materials. Structural, compositional and morphological changes are analyzed using X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, inductively coupled plasma mass spectrometry and X‐ray photoelectron spectroscopy. Our findings provide insights into the complexities of recycling ASSBs, but also highlight the potential for developing efficient, sustainable recycling processes.Item Open Access Synthesis and optical properties of single‐crystalline phosphors Gd3In2Ga3O12:RE3+ (RE = Nd3+ and Ho3+) grown via the optical float zone method(2025) Yilmaz, Hasan; Kinik, Gülsüm; Isobe, Masahiko; Puphal, Pascal; Suta, Markus; Clemens, OliverThe continuous development of innovative optical materials with lanthanoid ions as activators has emerged as a modern sector of materials chemistry. The experience with the fabrication of single crystals with the optical float zone has motivated one to investigate the luminescence of Nd3+ and Ho3+ ions in the garnets (Gd3−xREx)In2Ga3O12 (RE = Nd and Ho, x = 0; 0.15–0.30). Upon usage of an Ar/O2 (80:20 ratio) atmosphere and application of an auxiliary pressure (6 bar) to suppress In2O3 evaporation, single‐crystalline domain sizes in the order of ≈6 × 6 × 1 mm3 are obtained. Structural analysis confirms the formation of a cubic garnet phase with space group Ia3¯d, with the substituents incorporated in accordance with Vegard's law. Backscattered electron imaging and energy‐dispersive X‐ray spectroscopy are conducted, demonstrating a homogeneous elemental distribution within the crystals. Photoluminescence studies are carried out, revealing the characteristic narrow‐line 4fn → 4fn transitions of Nd3+ and Ho3+, with decay times in the submillisecond range, suggesting non‐negligible cross‐relaxation effects are present. Despite this, the large nearest‐neighbor Gd-Gd distance (3.88 Å) in Gd3In2Ga3O12 and the low phonon cutoff energy (≈700 cm-1) are found to limit cross‐relaxation pathways, preserving significant photoluminescence brightness. These results highlight the potential of Gd3In2Ga3O12:RE3+ single crystals as promising candidates for advanced optical applications.