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Physically based Impedance Modelling of Lithium-Ion Cells
In this book, a new procedure to analyze lithium-ion cells is introduced. The cells are disassembled to analyze their components in experimental cell housings. Then, Electrochemical Impedance Spectroscopy, time domain measurements and the Distribution function of Relaxation Times are applied to obtain a deep understanding of the relevant loss processes. This procedure yields a notable surplus of information about the electrode contributions to the overall internal resistance of the cell.
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Microstructural Characterisation, Modelling and Simulation of Solid Oxide Fuel Cell Cathodes
This work deals with microstructural characterisation, modelling and simulation of SOFC electrodes with the goal of optimizing the electrode microstructures. Methods for a detailed electrode analysis based on focused ion beam (FIB) tomography are presented. A 3D FEM model able to perform simulations of LSCF cathodes based on 3D tomography data is shown. A model generating realistic, yet synthetic microstructures is presented that enables the optimization of microstructural characteristics.
Verfahren zur Charakterisierung des Niederfrequenzverhaltens von Lithium-Ionen Batterien
In order to understand the current-voltage behaviour of a Lithium-Ion Battery, its impedance needs to be investigated in the low-frequency domain. This work deals with measurement, modelling and model validation in that low-frequency domain and introduces the Distribution-Function-of-Differential-Capacity (DDC) as a new tool for investigating capacity contributions of different particle sizes and particle types inside of a Lithium-Ion Battery.
Electrochemical Performance and Stability of Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ for Oxygen Transport Membranes
Mixed ionic-electronic conducting (MIEC) ceramics as oxygen transport membranes (OTMs) can provide high oxygen permeation rates at comparably low energy demands. For this purpose, Ba?.?Sr?.?Co?.?Fe?.?O??? (BSCF) shows the best performance under ideal operating conditions. Thermal and chemical stability investigations, electrical behavior ?(T,pO?,t), and oxygen exchange parameter extraction by means of electrical conductivity relaxation resulted in a far better understanding of the BSCF system.
Finite Element Method (FEM) Model and Performance Analysis of Solid Oxide Fuel Cells
This work presents a numerical FEM framework, capable of predicting SOFC performance under technically relevant, planar stack contacting conditions. A high level of confidence in the model predictions is supplied by using exclusively experimentally determined material/kinetic parameters and by a comprehensive validation. The presented model aids SOFC stack development by pre-evaluating possible material choices and design combinations for cells/interconnectors without any experimental effort.
Impedanzbasierte Spannungsprädiktion von Lithium-Ionen-Batterien
Diese Arbeit präsentiert ein physikalisch motiviertes Modell, welches die Zellspannung einer Lithium-Ionen-Batterie auf Basis der Zellimpedanz vorhersagt. Das Modell wurde an einer kommerziellen Pouchzelle parametriert und validiert. In einer umfassenden Simulationsstudie wird der Einfluss der Elektrodenmikrostruktur auf die Energie- und Leistungsdichte der Zelle quantifiziert. Darüber hinaus wird eine Routine zur Entwicklung anwendungsspezifischer Zelldesigns vorgestellt. - This work presents a physically motivated model that predicts the cell voltage of a lithium-ion-battery based on its impedance. The model was parameterized and validated on a commercial pouch cell. In a comprehensive simulation study, the influence of the electrode microstructure parameters on the energy and power density is quantified. Furthermore, a routine for the development of application-specific cell designs is developed.
Fast Electrochemical Impedance Spectroscopy
This book offers a review of electrochemical impedance spectroscopy (EIS) and its application in online condition monitoring of electrochemical devices, focusing on the practicalities of performing fast and accurate EIS. The first part of the book addresses the theoretical aspects of the fast EIS technique, including stochastic excitation signals, time-frequency signal processing, and statistical analysis of impedance measurements. The second part presents an application of the fast EIS technique for condition monitoring and evaluates the performance of the proposed fast EIS methodology in three different types of electrochemical devices: a Li-ion battery, a Li-S cell, and a polymer electrolyte membrane (PEM) fuel cell. Uniquely, in addition to theoretical aspects the book provides practical guidelines for implementation, commissioning, and exploitation of EIS for condition monitoring of electrochemical devices, making it a valuable resource for practicing engineers as well as researchers.
Charakterisierung und Modellierung der waessrigen Lithium-Luft Batterie
To estimate the reachable specific energy and power of aqueous Li-air batteries, a physical based model was developed, which for the first time includes the microstructure of Li-air cells. Parameters like solid/liquid interface resistances were quantified with help of a newly developed setup. Simulations based on the developed model revealed that even conservative estimations promise an increase in the specific energy by at least a factor of two compared to present Li-ion batteries.
Mikrostrukturelle Charakterisierung, Modellentwicklung und Simulation poroeser Elektroden fuer Lithiumionenzellen
Die Elektrodenmikrostrukturen einer Hochenergie- und einer Hochleistungs-Lithiumionenzelle wurden mit tomographischen Verfahren in 3D erfasst und auf Basis aussagekräftiger Strukturparameter quantitativ miteinander verglichen. Zur Simulation ihres elektrochemischen Verhaltens wurde ein FEM-Modell entwickelt, das erstmals eine reale Partikelgrößenverteilung beinhaltet. Dies erlaubt die Identifikation der begrenzenden Mechanismen während der (Ent-)Ladeprozesse in den Elektroden beider Zelltypen.
