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Validated Modelling of Electrochemical Energy Storage Devices
KTH, School of Engineering Sciences (SCI), Mechanics.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis aims at formulating and validating models for electrochemical energy storage devices. More specifically, the devices under consideration are lithium ion batteries and polymer electrolyte fuel cells.

A model is formulated to describe an experimental cell setup consisting of a LixNi0.8Co0.15Al0.05O2 composite porous electrode with three porous separators and a reference electrode between a current collector and a pure Li planar electrode. The purpose of the study being the identification of possible degradation mechanisms in the cell, the model contains contact resistances between the electronic conductor and the intercalation particles of the porous electrode and between the current collector and the porous electrode. On the basis of this model formulation, an analytical solution is derived for the impedances between each pair of electrodes in the cell. The impedance formulation is used to analyse experimental data obtained for fresh and aged LixNi0.8Co0.15Al0.05O2 composite porous electrodes. Ageing scenarios are formulated based on experimental observations and related published electrochemical and material characterisation studies. A hybrid genetic optimisation technique is used to simultaneously fit the model to the impedance spectra of the fresh, and subsequently also to the aged, electrode at three states of charge. The parameter fitting results in good representations of the experimental impedance spectra by the fitted ones, with the fitted parameter values comparing well to literature values and supporting the assumed ageing scenario.

Furthermore, a steady state model for a polymer electrolyte fuel cell is studied under idealised conditions. The cell is assumed to be fed with reactant gases at sufficiently high stoichiometric rates to ensure uniform conditions everywhere in the flow fields such that only the physical phenomena in the porous backings, the porous electrodes and the polymer electrolyte membrane need to be considered. Emphasis is put on how spatially resolved porous electrodes and nonequilibrium water transport across the interface between the gas phase and the ionic conductor affect the model results for the performance of the cell. The future use of the model in higher dimensions and necessary steps towards its validation are briefly discussed.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , vi, 28 p.
Series
Trita-MEK, ISSN 0348-467X ; 2009:12
Keyword [en]
lithium ion battery, polymer electrolyte fuel cell, modelling, model validation, parameter fitting
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-11052ISBN: 978-91-7415-423-8 (print)OAI: oai:DiVA.org:kth-11052DiVA: diva2:235087
Presentation
2009-09-25, D3, Lindstedtsvägen 5, Stockholm, 10:15 (English)
Opponent
Supervisors
Available from: 2009-09-15 Created: 2009-09-12 Last updated: 2010-10-19Bibliographically approved
List of papers
1. Impedance as a Tool for Investigating Aging in Lithium-Ion Porous Electrodes: I. Physically Based Electrochemical Model
Open this publication in new window or tab >>Impedance as a Tool for Investigating Aging in Lithium-Ion Porous Electrodes: I. Physically Based Electrochemical Model
2008 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 155, no 4, A304-A319 p.Article in journal (Refereed) Published
Abstract [en]

Electrochemical impedance spectroscopy is potentially a powerful diagnostic tool for the investigation of the effects of aging in porous electrodes. A physically based three-electrode model was developed for a LixNi0.8Co0.15Al0.05O2 composite porous electrode with three porous separators and a reference electrode between a current collector and a plane electrode. Two effects of aging were modeled for this particular electrode chemistry, namely, a resistive corrosion layer on the current collector and a contact resistance between the electronic conductor and the active material of the porous electrode. The derivation of an analytical solution for the impedances between each pair of electrodes in this model yielded a computationally fast, versatile, and modular formulation. The solution was used to study the impact of selected components of the physical model on the impedance spectrum of the porous electrode for a physically relevant base case. Approximating the active material particles as spherical or flake-shaped particles, lognormally or Dirac distributed in size, revealed that the distribution has a negligible impact while the shape makes a noticeable difference. The main aging-related parameters were shown to have quite distinct effects on the impedance spectrum, which is essential for the regression of experimental data and the study of aging hypotheses.

Place, publisher, year, edition, pages
PENNINGTON: ELECTROCHEMICAL SOC INC, 2008
Keyword
HIGH-POWER; ELECTROCHEMICAL IMPEDANCE; INTERCALATION PARTICLES; BATTERY ELECTROLYTES; CURRENT COLLECTORS; CAPACITY FADE; PASSIVE FILM; CELLS; ALUMINUM; CATHODES
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-8326 (URN)10.1149/1.2840015 (DOI)000253761700006 ()2-s2.0-40549116713 (Scopus ID)
Note
QC 20100618Available from: 2008-05-06 Created: 2008-05-06 Last updated: 2010-07-09Bibliographically approved
2. Impedance as a Tool for Investigating Aging in Lithium-Ion Porous Electrodes: II. Positive Electrode Examination
Open this publication in new window or tab >>Impedance as a Tool for Investigating Aging in Lithium-Ion Porous Electrodes: II. Positive Electrode Examination
2008 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 155, no 4, A320-A338 p.Article in journal (Refereed) Published
Abstract [en]

High-power positive LixNi0.8Co0.15Al0.05O2 composite porous electrodes are known to be the main source of impedance increase in batteries based on GEN2 chemistry. The impedance of positive electrodes, both fresh and harvested from coin cells aged in an accelerated EUCAR hybrid electric vehicle lifetime matrix, was measured in a three-electrode setup and the results fitted with a physically based impedance model. A methodology for fitting the impedance data, including an optimization strategy incorporating a global genetic routine, was used to fit either fresh or aged positive electrodes simultaneously at different states of charge down to 0.5 mHz. The fresh electrodes had an exchange current density of approximately 1.0 A m(-2), a solid-phase diffusion coefficient of approximately 1.4 x 10(-1)5 m(2) s(-1), and a log-normal active particle size distribution with a mean radius of 0.25 mu m. Aged electrode impedance results were shown to be highly dependent on both the electrode state of charge and the pressure applied to the electrode surface. An aging scenario incorporating loss of active particles, coupled with an increase both in the local contact resistance between the active material and the conductive carbon and the resistance of a layer on the current collector, was shown to be adequate in describing the measured aged electrode impedance behavior.

Keyword
X-RAY-DIFFRACTION; HIGH-POWER; CURRENT COLLECTORS; BATTERY ELECTROLYTES; CATHODE COMPOSITION; STRESS GENERATION; SOLID-SOLUTIONS; INSERTION CELL; CAPACITY FADE; PASSIVE FILM
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-8327 (URN)10.1149/1.2832654 (DOI)000253761700007 ()2-s2.0-40549091380 (Scopus ID)
Note
QC 20100618Available from: 2008-05-06 Created: 2008-05-06 Last updated: 2010-07-09Bibliographically approved
3. Porous Electrode and Nonequilibrium Water Transport Modelling in Polymer Electrolyte Fuel Cells
Open this publication in new window or tab >>Porous Electrode and Nonequilibrium Water Transport Modelling in Polymer Electrolyte Fuel Cells
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Recent years have seen the appearance of numerous modelling studies of the polymer electrolyte fuel cell. However, in spite of observations in different studies that a model for a cell operating under single-phase conditions must include nonequilibrium water transport and must spatially resolve the porous electrodes in order to capture the behaviour of the cell correctly, there are only very few models in the literature that simultaneously do both. This paper, however, formulates such a model and considers a one-dimensional version of it in a parameter study. In future work, the model will be used to calibrate model parameters against experiments and study the operation of cells in higher dimensions.

Keyword
polymer electrolyte fuel cell, modelling, porous electrode, nonequilibrium water transport
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-11050 (URN)
Note
QC 20101019Available from: 2009-09-12 Created: 2009-09-12 Last updated: 2010-10-19Bibliographically approved

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