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Ziel des Projekts STABIL war die Vorhersage der Alterung und Verbesserung der Lebensdauer von mobilen und stationären Lithium-Ionen-Batterien. Batterien sind zentrale Komponenten der Elektromobilität und der stationären Speicherung von regenerativem Strom. Die im Stand der Technik unzureichende Lebensdauer der Batterie ist heute wesentlicher Kostentreiber. Im Projekt wurde daher in einem skalenübergreifenden und interdisziplinären Ansatz das Verhalten von einzelnen Batteriezellen und ganzen Batteriesystemen unter zwei unterschiedlichen systemischen Randbedingungen untersucht.
Modeling and simulation play a key role in analyzing the complex electrochemical behavior of lithium-ion batteries. We present the development of a thermodynamic and kinetic modeling framework for intercalation electrochemistry within the open-source software Cantera. Instead of using equilibrium potentials and single-step Butler-Volmer kinetics, Cantera is based on molar thermodynamic data and mass-action kinetics, providing a physically-based and flexible means for complex reaction pathways. Herein, we introduce a new thermodynamic class for intercalation materials into the open-source software. We discuss the derivation of molar thermodynamic data from experimental half-cell potentials, and provide practical guidelines. We then demonstrate the new class using a single-particle model of a lithium cobalt oxide/graphite lithium-ion cell, implemented in MATLAB. With the present extensions, Cantera provides a platform for the lithium-ion battery modeling community both for consistent thermodynamic and kinetic models and for exchanging the required thermodynamic and kinetic parameters. We provide the full MATLAB code and parameter files as supplementary material to this article.
Model-based analysis of Electrochemical Pressure Impedance Spectroscopy (EPIS) for PEM Fuel Cells
(2019)
Electrochemical impedance spectroscopy (EIS) is a widely-used diagnostic technique to characterize electrochemical processes. It is based on the dynamic analysis of two electrical observables, that is, current and voltage. Electrochemical cells with gaseous reactants or products, in particular fuel cells, offer an additional observable, that is, the gas pressure. The dynamic coupling of current or voltage with gas pressure gives rise to a number of additional impedance definitions, for which we have previously introduced the term electrochemical pressure impedance spectroscopy (EPIS) [1,2]. EPIS shows a particular sensitivity towards transport processes of gas-phase or dissolved species, in particular, diffusion coefficients and transport pathway lengths. It is as such complementary to standard EIS, which is mainly sensitive towards electrochemical processes. First EPIS experiments on PEM fuel cells have recently been shown [3].
We present a detailed modeling and simulation analysis of EPIS of a PEM fuel cell. We use a 1D+1D continuum model of a fuel/air channel pair with GDL and MEA. Backpressure is dynamically varied, and the resulting simulated oscillation in cell voltage is evaluated to yield the ▁Z_( V⁄p_ca ) EPIS signal. Results are obtained for different transport situations of the fuel cell, giving rise to very complex EPIS shapes in the Nyquist plot. This complexity shows the necessity of model-based interpretation of the complex EPIS shapes. Based on the simulation results, specific features in the EPIS spectra can be assigned to different transport domains (gas channel, GDL, membrane water transport).
Ziel des LiBaLu-Teilprojekts Modellierung und Simulation war die Unterstützung der Elektroden- und Zellentwicklung mit Hilfe umfangreicher Computersimulationen im Sinne des computergestützten Engineering (CAE). Zwei verschiedene Schwerpunkte standen im Mittelpunkt der Untersuchungen. Zum einen wurde das mechanistische Verständnis der komplexen Elektrochemie in Lithium-Luftbatterien durch mikrokinetische Modelle aufgeklärt. Auf Basis von postulierten Mehrschrittmechanismen wurden makroskopische Eigenschaften (Entlade-/Ladekennlinien, Zyklovoltammogramme) vorhergesagt und mit experimentellen Daten der Projektpartner verglichen. Zum anderen wurde das Design der Prototypzelle mit Hilfe numerischer Simulationen untersucht und optimiert. So konnten z. B. optimale Schichtdicken oder die Rolle von Gastransportlimitierungen identifiziert werden.