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Impedance as a Tool for Investigating Aging in Lithium-Ion Porous Electrodes: II. Positive Electrode Examination
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-8318-1251
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0001-9203-9313
2008 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, 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.

Place, publisher, year, edition, pages
2008. Vol. 155, no 4, A320-A338 p.
Keyword [en]
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: urn:nbn:se:kth:diva-8327DOI: 10.1149/1.2832654ISI: 000253761700007Scopus ID: 2-s2.0-40549091380OAI: oai:DiVA.org:kth-8327DiVA: diva2:13619
Note
QC 20100618Available from: 2008-05-06 Created: 2008-05-06 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Diagnosis of the Lifetime Performance Degradation of Lithium-Ion Batteries: Focus on Power-Assist Hybrid Electric Vehicle and Low-Earth-Orbit Satellite Applications
Open this publication in new window or tab >>Diagnosis of the Lifetime Performance Degradation of Lithium-Ion Batteries: Focus on Power-Assist Hybrid Electric Vehicle and Low-Earth-Orbit Satellite Applications
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Lithium-ion batteries are a possible choice for the energy storage system onboard hybrid electric vehicles and low-earth-orbit satellites, but lifetime performance remains an issue. The challenge is to diagnose the effects of ageing and then investigate the dependence of the magnitude of the deterioration on different accelerating factors (e.g. state-of-charge (SOC), depth-of-discharge (DOD) and temperature).

Lifetime studies were undertaken incorporating different accelerating factors for two different applications: (1) coin cells with a LixNi0.8Co0.15Al0.05O2-based positive electrode were studied with a EUCAR power-assist HEV cycle, and (2) laminated commercial cells with a LixMn2O4-based positive electrode were studied with a low-earth-orbit (LEO) satellite cycle. Cells were disassembled and the electrochemical performance of harvested electrodes measured with two- and three-electrode cells. The LixNi0.8Co0.15Al0.05O2-based electrode impedance results were interpreted with a physically-based three-electrode model incorporating justifiable effects of ageing.

The performance degradation of the cells with nickelate chemistry was independent of the cycling condition or target SOC, but strongly dependent on the temperature. The positive electrode was identified as the main source of impedance increase, with surface films having a composition that was independent of the target SOC, but with more of the same species present at higher temperatures. Furthermore, impedance results were shown to be highly dependent on both the electrode SOC during the measurement and the pressure applied to the electrode surface. An ageing hypothesis incorporating a resistive layer on the current collector and a local contact resistance (dependent on SOC) between the carbon and active material, both possibly leading to particle isolation, was found to be adequate in fitting the harvested aged electrode impedance data.

The performance degradation of the cells with manganese chemistry was accelerated by both higher temperatures and larger DODs. The impedance increase was small, manifested in a SOC-dependent increase of the high-frequency semicircle and a noticeable increase of the high-frequency real axis intercept. The positive electrode had a larger decrease in capacity and increase in the magnitude of the high-frequency semi-circle (particularly at high intercalated lithium-ion concentrations) in comparison with the negative electrode. This SOC-dependent change was associated with cells cycled for either extended periods of time or at higher temperatures with a large DOD. An observed change of the cycling behaviour in the second potential plateau for the LixMn2O4-based electrode provided a possible kinetic-based explanation for the change of the high-frequency semi-circle.

Abstract [sv]

Litiumjonbatteriet är en möjlig kandidat för energilagring i hybridfordon och i satelliter i låg omloppsbana, men än så länge är livslängden på batterierna ett problem. Utmaningen ligger i att kunna förstå hur batteriet åldras genom att utforska hur åldringsprocessen accelereras av faktorer som laddningstillstånd, urladdningsdjup och temperatur.

Livslängdsstudier för två olika typer av batterier tänkta för olika applikationer utfördes: (1) knappceller med positiva LixNi0,8Co0,15Al0,05O2-baserade elektroder studerades med en effektstödd (power-assist) hybridcykel från EUCAR, och (2) laminerade kommersiella celler med positiva LixMn2O4-baserade elektroder studerades med en satellitcykel, avsedd för en satellit med låg omloppsbana. Cellerna öppnades och de uttagna elektrodernas elektrokemiska egenskaper utvärderades i två- och tre-elektroduppställningar. Resultaten från elektrokemiska impedansmätningar för den positiva LixNi0,8Co0,15Al0,05O2-baserade elektroden tolkades med hjälp av en fysikalisk tre-elektrod modell som tog hänsyn till de i litteraturen främst föreslagna effekterna av åldring.

Prestandadegraderingen av celler med nickelkemi var oberoende av cykel och laddningstillståndet där åldringen skedde, men starkt beroende av temperaturen. Den positiva elektroden visade sig vara den största orsaken till impedansökningen i batteriet. Ytfilmerna på den positiva elektroden hade en sammansättning som var oberoende av laddningstillståndet men beroende av temperaturen. Impedansresultaten från de uttagna elektroderna var starkt beroende av både laddningstillstånd och yttre tryck på elektrodytan. Det visade sig att det var tillräckligt att ta hänsyn till ett resistivt skikt på strömtilledaren och en lokal kontaktresistans mellan kolet och det aktiva materialet (som är beroende av laddningstillståndet) för att anpassa modellen till impedansdata mätt på de uttagna elektroderna.

Prestandadegraderingen av celler med mangankemi påskyndades av både högre temperaturer och högre urladdningsdjup. Impedansen ökade något, då både högfrekvenshalvcirkeln och högfrekvensintercepten ändrades. Positiva elektroden hade en större degradering i kapaciteten och en större ökning i magnituden av högfrekvenshalvcirkeln (speciellt vid högre litiumjon koncentrationer i elektroden) jämfört med den negativa elektroden. Denna laddningstillståndsberoende impedans-ökning var kopplad till celler som hade cyklats under en längre tid eller vid en högre temperatur och med ett högt urladdningsdjup. Ökningen i magnituden av högfrekvenshalvcirkeln skulle kunna vara relaterad till kinetiska begränsningar eftersom cyklingsbeteendet vid andra spänningsplatån ändrades samtidigt för de LixMn2O4-baserade elektroderna.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. x, 132 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:13
Keyword
lithium-ion battery, LixNi0.8Co0.15Al0.05O2, LixMn2O4, LiyC6, ageing, three-electrode measurements, impedance modelling, surface film characterisation, hybrid electric vehicle, low-earth-orbit satellite, litiumjonbatteri, åldring, treelektroduppställning, impedansmodell, ytfilmskarakterisering, hybridfordon, satelliter
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-4722 (URN)978-91-7178-875-7 (ISBN)
Public defence
2008-05-23, D2, Lindstedtsvägen 5, Entreplan, KTH, 10:00
Opponent
Supervisors
Note
QC 20100621Available from: 2008-05-06 Created: 2008-05-06 Last updated: 2010-07-13Bibliographically approved
2. Validated Modelling of Electrochemical Energy Storage Devices
Open this publication in new window or tab >>Validated Modelling of Electrochemical Energy Storage Devices
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
lithium ion battery, polymer electrolyte fuel cell, modelling, model validation, parameter fitting
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-11052 (URN)978-91-7415-423-8 (ISBN)
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

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