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A two-dimensional single-phase model is developed for the steady-state and transient analysis of polymer electrolyte membrane fuel cells (PEMFC). Based on diluted and concentrated solution theories, viscous flow is introduced into a phenomenological multi-component modeling framework in the membrane. Characteristic variables related to the water uptake are discussed. A Butler–Volmer formulation of the current-overpotential relationship is developed based on an elementary mechanism of electrochemical oxygen reduction. Validated by using published V–I experiments, the model is then used to analyze the effects of operating conditions on current output and water management, especially net water transport coefficient along the channel. For a power PEMFC, the long-channel configuration is helpful for internal humidification and anode water removal, operating in counterflow mode with proper gas flow rate and humidity. In time domain, a typical transient process with closed anode is also investigated.
The state-of-the-art electrochemical impedance spectroscopy (EIS) calculations have not yet started from fully multi-dimensional modeling. For a polymer electrolyte membrane fuel cell (PEMFC) with long flow channel, the impedance plot shows a multi-arc characteristic and some impedance arcs could merge. By using a step excitation/Fourier transform algorithm, an EIS simulation is implemented for the first time based on the full 2D PEMFC model presented in the first part of this work. All the dominant transient behaviors are able to be captured. A novel methodology called ‘configuration of system dynamics’, which is suitable for any electrochemical system, is then developed to resolve the physical meaning of the impedance spectra. In addition to the high-frequency arc due to charge transfer, the Nyquist plots contain additional medium/low-frequency arcs due to mass transfer in the diffusion layers and along the channel, as well as a low-frequency arc resulting from water transport in the membrane. In some case, the impedance spectra appear partly inductive due to water transport, which demonstrates the complexity of the water management of PEMFCs and the necessity of physics-based calculations.
Ziel der Investitionsmaßnahme Enerlab 4.0 war die Bereitstellung einer umfangreichen in-operando und post-mortem Diagnostik für dezentrale Energieerzeuger und -Speicher, z. B. Batteriezellen und Photovoltaikzellen. Diese sind wichtige Komponenten für verschiedene Bereiche der Industrie 4.0 – von autonomen Sensoren über energieautarke Produktion bis hin zur Qualitätskontrolle. Zu diesem Zweck wurde die apparative Ausstattung der Hochschule Offenburg erweitert, und zwar sowohl für in-operando Diagnostik (elektrische Zyklierer, Impedanzspektrometer, Temperaturprüfschränke) als auch für post-mortem Diagnostik (Glovebox, Probenpräparationen für vorhandene Werkstoffanalytik und chemische Analytik). Be-reits vorhandene Geräte aus anderen laufenden oder abgeschlossenen Projekten wurden in die neue Infrastruktur integriert. Im Ergebnis entstand ein modernes und leistungsfähiges Batterie- und Photovoltaiklabor, welches in zahlreichen laufenden und neuen Vorhaben genutzt wird.
Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Bestimmung des Ladezustandes (SOC) einer aufladbaren Batterie (106) eines vorgegebenen Batterietyps oder eines damit in einem physikalischen Zusammenhang stehenden Parameters, insbesondere einer in der Batterie enthaltenen Restladungsmenge Q, wobei das Verfahren mittels eines spannungsgeführten Batteriemodells (102) arbeitet, welches für die betreffende Batterie (106) oder einen entsprechenden Batterietyp parametriert wird. Es muss lediglich die Batteriespannung Umess gemessen und dem Batteriemodell (102) als Eingangsgröße zur Verfügung gestellt werden. Weiterhin betrifft die Erfindung ein Verfahren und eine Vorrichtung zur Bestimmung des Gesundheitszustandes (SOH) einer Batterie (102), wobei das Batteriemodell (102), das auch zur Bestimmung des SOC verwendet wird, einen modellierten Batteriestrom Imodliefert. Aus diesem können modellierte Ladungsmengen während Lade- und Entladephasen der Batterie (106) bestimmt und mit gemessenen Ladungsmengen, die aus dem gemessenen Batteriestrom Imessbestimmt werden, verglichen werden. Da das Batteriemodell (102) nicht altert, kann hierdurch der SOH der Batterie bestimmt werden.
Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur Bestimmung des Ladezustandes (SOC) einer aufladbaren Batterie (106) eines vorgegebenen Batterietyps oder eines damit in einem physikalischen Zusammenhang stehenden Parameters, insbesondere einer in der Batterie enthaltenen Restladungsmenge Q, wobei das Verfahren mittels eines spannungsgeführten Batteriemodells (102) arbeitet, welches für die betreffende Batterie (106) oder einen entsprechenden Batterietyp parametriert wird. Es muss lediglich die Batteriespannung Umess gemessen und dem Batteriemodell (102) als Eingangsgröße zur Verfügung gestellt werden. Weiterhin betrifft die Erfindung ein Verfahren und eine Vorrichtung zur Bestimmung des Gesundheitszustandes (SOH) einer Batterie (102), wobei das Batteriemodell (102), das auch zur Bestimmung des SOC verwendet wird, einen modellierten Batteriestrom Imodliefert. Aus diesem können modellierte Ladungsmengen während Lade- und Entladephasen der Batterie (106) bestimmt und mit gemessenen Ladungsmengen, die aus dem gemessenen Batteriestrom Imessbestimmt werden, verglichen werden. Da das Batteriemodell (102) nicht altert, kann hierdurch der SOH der Batterie bestimmt werden.
The invention relates to a method and to a device for determining the state of charge (SOC) of a rechargeable battery (106) of a specified battery type or a parameter physically related thereto, in particular a remaining charge amount Q contained in the battery, the method operating by means of a voltage-controlled battery model (102), which is parameterized for the battery (106) in question or a corresponding battery type. It is merely necessary to measure the battery voltage Umess and to provide said battery voltage to the battery model (102) as an input variable. The invention further relates to a method and to a device for determining the state of health (SOH) of a battery (102), wherein the battery model (102) also used to determine the SOC provides a modeled battery current Imod. Modeled charge amounts during charging and discharging phases of the battery (106) can be determined from said modeled battery current and can be compared with measured charge amounts, which are determined from the measured battery current Imess. Because the battery model (102) does not age, the SOH of the battery can thereby be determined.
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.
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.
Passive hybridization refers to a parallel connection of photovoltaic and battery cells on the direct current level without any active controllers or inverters. We present the first study of a lithium-ion battery cell connected in parallel to a string of four or five serially-connected photovoltaic cells. Experimental investigations were performed using a modified commercial photovoltaic module and a lithium titanate battery pouch cell, representing an overall 41.7 W-peak (photovoltaic)/36.8 W-hour (battery) passive hybrid system. Systematic and detailed monitoring of this system over periods of several days with different load scenarios was carried out. A scaled dynamic synthetic load representing a typical profile of a single-family house was successfully supplied with 100 % self-sufficiency over a period of two days. The system shows dynamic, fully passive self-regulation without maximum power point tracking and without battery management system. The feasibility of a photovoltaic/lithium-ion battery passive hybrid system could therefore be demonstrated.
Simulation-based degradation assessment of lithium-ion batteries in a hybrid electric vehicle
(2017)
The accurate diagnosis of state of charge (SOC) and state of health (SOH) is of utmost importance for battery users and for battery manufacturers. State diagnosis is commonly based on measuring battery current and using it in Coulomb counters or as input for a current-controlled model. Here we introduce a new algorithm based on measuring battery voltage and using it as input for a voltage-controlled model. We demonstrate the algorithm using fresh and pre-aged lithium-ion battery single cells operated under well-defined laboratory conditions on full cycles, shallow cycles, and a dynamic battery electric vehicle load profile. We show that both SOC and SOH are accurately estimated using a simple equivalent circuit model. The new algorithm is self-calibrating, is robust with respect to cell aging, allows to estimate SOH from arbitrary load profiles, and is numerically simpler than state-of-the-art model-based methods.
Aqueous lithium–oxygen batteries are promising candidates for electric energy storage. In this paper we present and discuss a multiphase continuum model of an aqueous lithium–oxygen single cell including reactions and transport in a porous gas diffusion electrode (GDE). The model is parameterized using in-house half-cell experiments and available literature data on aqueous electrolytes. We validate our transport model with cyclic voltammetry and electrochemical impedance spectroscopy measurements over a wide range of temperatures (25, 40, 55 °C) and electrolyte concentrations (0.1–2 M). We observe very good agreement between simulations and measurements during oxygen reduction conditions. A sensitivity analysis of the validated model demonstrates the influence of the porous structure on GDE performance and gives directions for the future development of electrodes.
Seven cell design concepts for aqueous (alkaline) lithium–oxygen batteries are investigated using a multi-physics continuum model for predicting cell behavior and performance in terms of the specific energy and specific power. Two different silver-based cathode designs (a gas diffusion electrode and a flooded cathode) and three different separator designs (a porous separator, a stirred separator chamber, and a redox-flow separator) are compared. Cathode and separator thicknesses are varied over a wide range (50 μm–20 mm) in order to identify optimum configurations. All designs show a considerable capacity-rate effect due to spatiotemporally inhomogeneous precipitation of solid discharge product LiOH·H2O. In addition, a cell design with flooded cathode and redox-flow separator including oxygen uptake within the external tank is suggested. For this design, the model predicts specific power up to 33 W/kg and specific energy up to 570 Wh/kg (gravimetric values of discharged cell including all cell components and catholyte except housing and piping).
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 (e.g., fuel cells, metal/air cells, electrolyzers) offer an additional observable, that is, the gas pressure. The dynamic coupling of current and/or voltage with gas pressure gives rise to a number of additional impedance definitions, for which we have 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. This sensitivity can be exploited for model parameterization and validation. A general analysis of EPIS is presented, which shows the necessity of model-based interpretation of the complex EPIS shapes in the Nyquist plot (cf. Figure). We then present EPIS simulations for two different electrochemical cells: (1) a sodium/oxygen battery cell and (2) a hydrogen/air fuel cell. We use 1D or 2D electrochemical and transport models to simulate current excitation/pressure detection or pressure excitation/voltage detection. The results are compared to first EPIS experimental data available in literature [2,3].