05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Analytic free-energy expression for the 2D-Ising model and perspectives for battery modeling(2023) Markthaler, Daniel; Birke, Kai PeterAlthough originally developed to describe the magnetic behavior of matter, the Ising model represents one of the most widely used physical models, with applications in almost all scientific areas. Even after 100 years, the model still poses challenges and is the subject of active research. In this work, we address the question of whether it is possible to describe the free energy A of a finite-size 2D-Ising model of arbitrary size, based on a couple of analytically solvable 1D-Ising chains. The presented novel approach is based on rigorous statistical-thermodynamic principles and involves modeling the free energy contribution of an added inter-chain bond DAbond(b, N) as function of inverse temperature b and lattice size N. The identified simple analytic expression for DAbond is fitted to exact results of a series of finite-size quadratic N N-systems and enables straightforward and instantaneous calculation of thermodynamic quantities of interest, such as free energy and heat capacity for systems of an arbitrary size. This approach is not only interesting from a fundamental perspective with respect to the possible transfer to a 3D-Ising model, but also from an application-driven viewpoint in the context of (Li-ion) batteries where it could be applied to describe intercalation mechanisms.Item Open Access Modeling and experimental investigation of the interaction between pressure-dependent aging and pressure development due to the aging of lithium-ion cells(2023) Avdyli, Arber; Fill, Alexander; Birke, Kai PeterIn order to meet the increasing demands of the battery in terms of range, safety and performance, it is necessary to ensure optimal operation conditions of a lithium-ion cell. In this thesis, the influence of mechanical boundary conditions on the cell is investigated theoretically and experimentally. First, fundamental equations are derived that lead to coupled models that can be parameterized based on specific cell measurements and predict the pressure evolution due to capacity aging and vice versa. The model is used to derive optimal operating points of the cell, which can be considered in the module design.Item Open Access Surface charge density and induced currents by self-charging sliding drops(2024) Bista, Pravash; Ratschow, Aaron D.; Stetten, Amy Z.; Butt, Hans-Jürgen; Weber, Stefan A. L.Spontaneous charge separation in drops sliding over a hydrophobized insulator surface is a well-known phenomenon and lots of efforts have been made to utilize this effect for energy harvesting. For maximizing the efficiency of such devices, a comprehensive understanding of the dewetted surface charge would be required to quantitatively predict the electric current signals, in particular for drop sequences. Here, we use a method based on mirror charge detection to locally measure the surface charge density after drops move over a hydrophobic surface. For this purpose, we position a metal electrode beneath the hydrophobic substrate to measure the capacitive current induced by the moving drop. Furthermore, we investigate drop-induced charging on different dielectric surfaces together with the surface neutralization processes. The surface neutralizes over a characteristic time, which is influenced by the substrate and the surrounding environment. We present an analytical model that describes the slide electrification using measurable parameters such as the surface charge density and its neutralization time. Understanding the model parameters and refining them will enable a targeted optimization of the efficiency in solid–liquid charge separation.Item Open Access Cycling of double-layered graphite anodes in pouch-cells(2022) Müller, Daniel; Fill, Alexander; Birke, Kai PeterIncremental improvement to the current state-of-the-art lithium-ion technology, for example regarding the physical or electrochemical design, can bridge the gap until the next generation of cells are ready to take Li-ions place. Previously designed two-layered porosity-graded graphite anodes, together with LixNi0.6Mn0.2Co0.2O2 cathodes, were analysed in small pouch-cells with a capacity of around 1 Ah. For comparison, custom-made reference cells with the average properties of two-layered anodes were tested. Ten cells of each type were examined in total. Each cell pair, consisting of one double-layer and one single-layer (reference) cell, underwent the same test procedure. Besides regular charge and discharge cycles, electrochemical impedance spectroscopy, incremental capacity analysis, differential voltage analysis and current-pulse measurement are used to identify the differences in ageing behaviour between the two cell types. The results show similar behaviour and properties at beginning-of-life, but an astonishing improvement in capacity retention for the double-layer cells regardless of the cycling conditions. Additionally, the lifetime of the single-layer cells was strongly influenced by the cycling conditions, and the double-layer cells showed less difference in ageing behaviour.Item Open Access Introducing a concept for designing an aqueous electrolyte with pH buffer properties for Zn-MnO2 batteries with Mn2+/MnO2 deposition/dissolution(2023) Fitz, Oliver; Wagner, Florian; Pross-Brakhage, Julia; Bauer, Manuel; Gentischer, Harald; Birke, Kai Peter; Biro, DanielFor large-scale energy-storage systems, the aqueous rechargeable zinc–manganese dioxide battery (ARZMB) attracts increasing attention due to its excellent advantages such as high energy density, high safety, low material cost, and environmental friendliness. Still, the reaction mechanism and its influence on the electrolyte's pH are under debate. Herein, a pH buffer concept for ARZMB electrolytes is introduced. Selection criteria for pH buffer substances are defined. Different buffered electrolytes based on a zinc salt (ZnSO4, Zn(CH3COO)2, Zn(CHOO)2), and pH buffer substances (acetic acid, propionic acid, formic acid, citric acid, 4-hydrobenzoic acid, potassium bisulfate, potassium dihydrogen citrate, and potassium hydrogen phthalate) are selected and compared to an unbuffered 2 m ZnSO4 reference electrolyte using titration, galvanostatic cycling with pH tracking, and cyclic voltammetry. By adding buffer substances, the pH changes can be reduced and controlled within the defined operating window, supporting the Mn2+/MnO2 deposition/dissolution mechanism. Furthermore, the potential plateau during discharge can be increased from ≈1.3 V (ZnSO4) to ≈1.7 V (ZnSO4 + AA) versus Zn/Zn2+ and the energy retention from ≈30% after 268 cycles (ZnSO4) to ≈86% after 494 cycles (ZnSO4 + AA). Herein, this work can serve as a basis for the targeted design of long-term stable ARZMB electrolytes.Item Open Access Coordination chemistry as a universal strategy for a controlled perovskite crystallization(2023) Zuo, Weiwei; Byranvand, Mahdi Malekshahi; Kodalle, Tim; Zohdi, Mohammadreza; Lim, Jaekeun; Carlsen, Brian; Magorian Friedlmeier, Theresa; Kot, Małgorzata; Das, Chittaranjan; Flege, Jan Ingo; Zong, Wansheng; Abate, Antonio; Sutter‐Fella, Carolin M.; Li, Meng; Saliba, MichaelThe most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI3 PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI3 as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.Item Open Access A high frequency alternating current heater using the advantages of a damped oscillation circuit for low voltage Li-ion batteries(2024) Oehl, Joachim; Gleiter, Andreas; Manka, Daniel; Fill, Alexander; Birke, Kai PeterIn many cases, batteries used in light e-mobility vehicles such as e-bikes and e-scooters do not have an active thermal management system. This poses a challenge when these batteries are stored in sub-zero temperatures and need to be charged. In such cases, it becomes necessary to move the batteries to a warmer location and allow them to acclimatize before charging. However, this is not always feasible, especially for batteries installed permanently in vehicles. In this work, we present an internal high-frequency AC heater for a 48 V battery, which is used for light electric vehicles of EU vehicle classes L1e and L3e-A1 for a power supply of up to 11 kW. We have taken advantage of the features of a damped oscillating circuit to improve the performance of the heater. Additionally, only a small inductor was added to the main current path through a cable with three windings. Furthermore, as the power electronics of the heater is part of the battery main switch, fewer additional parts inside the battery are required and therefore a cost and space reduction compared to other heaters is possible. For the chosen setup we reached a heating rate of up to 2.13 K min -1 and it was possible to raise the battery temperature from -10 °C to 10 °C using only 3.1% of its own usable capacity.Item Open Access Untersuchung von Parallelschaltungen unterschiedlich gealterter Zellmodule(2024) Kreher, Tina; Birke, Kai Peter (Prof. Dr.-Ing.)In dieser Arbeit wird das Thema „Untersuchung von Parallelschaltungen unterschiedlich gealterter Zellmodule“ im Rahmen von drei Themengebieten betrachtet. Es handelt sich dabei um Untersuchungen an parallelgeschalteten Lithium-Ionen-Zellen oder darauf basierenden Batteriesystemen. Der erste Teil untersucht das Potential die Messzeit zur Messdatenerhebung für die Parametrierung eines Ersatzschaltbildes zu reduzieren. Dafür werden verschiedene Charakterisierungsmethoden angewandt und die daraus erstellten Modelle hinsichtlich Genauigkeit und zeitlichem Messaufwand verglichen. Es zeigt sich, dass durch eine geschickte Wahl der Vorgehensweise die benötigte Messzeit und die damit verbundenen Kosten um bis zu 76 % reduziert werden können, ohne einen nennenswerten Nachteil auf die Modellgenauigkeit zu erhalten. Im zweiten Teil der Arbeit finden kalendarische und zyklische Alterungstests statt. Anhand der gewonnenen Daten werden Stressfaktoren der Zellalterung identifiziert und quantifiziert. Die Ergebnisse führen starke Alterung auf hohe Temperaturen und Ladezustände sowie große Zyklentiefen zurück. Des Weiteren wird ein Alterungsmodell erstellt, mit welchem die Alterung von Ersatzschaltbildparametern nachgebildet werden kann. Die eigentlichen Untersuchungen zu Parallelschaltungen finden im dritten Teil statt und bauen auf den Ergebnissen aus den ersten beiden Teilen auf. Zunächst wird ein Simulationsmodell aufgebaut und validiert, welches ein Parallelschaltungssystem aus zwei Lithium-Ionen-Zellen darstellt. Im nächsten Schritt erfolgt die Betrachtung einer ungesteuerten Parallelschaltung aus Zellen unterschiedlichen Alterungszustands, bei welcher mit einer inhomogenen Zellstromaufteilung zu rechnen ist. Dabei ist mit zunehmender Alterungsdifferenz der Zellen eine Lastverschiebung hin zur neueren Zelle festzustellen. Bezogen auf die Alterung zeigt sich eine bis zu 1,24-fach stärkere Kapazitätsabnahme und ein 1,33-facher Innenwiderstandsanstieg der neueren Zelle im Vergleich zu einem System mit gleichen Zellzuständen und homogener Stromaufteilung. Als nächstes findet die Ausarbeitung einer Betriebsstrategie für eine gesteuerte Parallelschaltung anhand eines möglichen Anwendungsfalls statt. Dafür wird implementiert, dass ein Parallelbetrieb beider Zellen, wie auch das gezielte Zu- und Wegschalten von einzelnen Strängen im System zulässig ist. Die Ergebnisse zeigen, dass so ein sicherer Betrieb von Parallelschaltungen bestehend aus unterschiedlich stark gealterten Zellen möglich ist. Die auf Zellebene gewonnenen Ergebnisse zu Parallelschaltungen werden im Rahmen eines Forschungsprojekt auf eine Fahrzeuganwendung mit zwei autarken Batterien unterschiedlichen Alterungszustandes übertragen. Zusammen mit dem Projektpartner erfolgt der Aufbau eines Prototyps, bei welchem der Parallelbetrieb und das gezielte An- und Abkoppeln der Batterien an das Hochvoltsystem möglich ist. Dieser Aufbau dient als Machbarkeitsnachweis für den Parallelbetrieb von Lithium-Ionen-Zellen und Batterien mit unterschiedlichen Alterungszuständen.Item Open Access Laser doping for silicon solar cells : modeling and application(2024) Hassan, Mohamed; Werner, Jürgen H. (Prof. Dr. rer. nat. habil.)In meiner Dissertation geht es um die Simulation des Laserdotierungsprozess der Oberfläche des Siliziumwafers um hoch effizienten Solarzellen herzustellen. Die Simulation ermöglicht die genaue Vorhersage der Dimensionen eines dotierten Bereiches. Das hat ermöglicht, nicht nur die Abhängigkeit des ergebenden Schichtleitwerts von der benutzten Rastergeschwindigkeit des Laserstrahls auf die Siliziumoberfläche zu verstehen, sondern auch der Schichtleitwert einer laserdotierten Schicht basierend auf ein einfaches geometrisches Modell vorherzusagen.Item Open Access Laser activation for highly boron-doped passivated contacts(2023) Sharbaf Kalaghichi, Saman; Hoß, Jan; Zapf-Gottwick, Renate; Werner, Jürgen H.Passivated, selective contacts in silicon solar cells consist of a double layer of highly doped polycrystalline silicon (poly Si) and thin interfacial silicon dioxide (SiO2). This design concept allows for the highest efficiencies. Here, we report on a selective laser activation process, resulting in highly doped p++-type poly Si on top of the SiO2. In this double-layer structure, the p++-poly Si layer serves as a layer for transporting the generated holes from the bulk to a metal contact and, therefore, needs to be highly conductive for holes. High boron-doping of the poly Si layers is one approach to establish the desired high conductivity. In a laser activation step, a laser pulse melts the poly Si layer, and subsequent rapid cooling of the Si melt enables electrically active boron concentrations exceeding the solid solubility limit. In addition to the high conductivity, the high active boron concentration in the poly Si layer allows maskless patterning of p++-poly Si/SiO2 layers by providing an etch stop layer in the Si etchant solution, which results in a locally structured p++-poly Si/SiO2 after the etching process. The challenge in the laser activation technique is not to destroy the thin SiO2, which necessitates fine tuning of the laser process. In order to find the optimal processing window, we test laser pulse energy densities (Hp) in a broad range of 0.7 J/cm2 ≤ Hp ≤ 5 J/cm2 on poly Si layers with two different thicknesses dpoly Si,1 = 155 nm and dpoly Si,2 = 264 nm. Finally, the processing window 2.8 J/cm2≤ Hp ≤ 4 J/cm2 leads to the highest sheet conductance (Gsh) without destroying the SiO2 for both poly Si layer thicknesses. For both tested poly Si layers, the majority of the symmetric lifetime samples processed using these Hp achieve a good passivation quality with a high implied open circuit voltage (iVOC) and a low saturation current density (J0). The best sample achieves iVOC = 722 mV and J0 = 6.7 fA/cm2 per side. This low surface recombination current density, together with the accompanying measurements of the doping profiles, suggests that the SiO2 is not damaged during the laser process. We also observe that the passivation quality is independent of the tested poly Si layer thicknesses. The findings of this study show that laser-activated p++-poly Si/SiO2 are not only suitable for integration into advanced passivated contact solar cells, but also offer the possibility of maskless patterning of these stacks, substantially simplifying such solar cell production.