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Characterization of Lithium Intercalation Processes of PAN-based Carbon Fibers in a Microelectrode System
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-9698-4136
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0002-9392-9059
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-9203-9313
(English)Article in journal (Other academic) Submitted
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-122398OAI: oai:DiVA.org:kth-122398DiVA: diva2:622110
Funder
StandUp
Note

QC 20160622

Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2016-06-22Bibliographically approved
In thesis
1. Mathematical Models for Investigation of Performance, Safety, and Aging in Lithium-Ion Batteries
Open this publication in new window or tab >>Mathematical Models for Investigation of Performance, Safety, and Aging in Lithium-Ion Batteries
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Rechargeable lithium-ion batteries have both the power and energy capabilities to be utilized in hybrid electric vehicles and other power demanding applications. However, there are obstacles primarily related to reliability in safety and lifetime. Additionally, there is still room for improvement in the battery performance.

In this work, physics-based mathematical models have been successfully set-up and numerically solved to investigate performance, safety, and aging in lithium-ion battery systems. This modeling approach enabled a detailed analysis of the electrochemical processes related to these issues. As the models included many parameters and spatial resolution of several variables with time or frequency, strategies for investigation needed to be developed for most of the work. The accuracy of the investigation was consolidated by the utilization of parameters characterized from experimental work.

The performance expressed in terms of polarization was determined for a power-optimized battery cell undergoing various operating conditions. A methodology that separated and quantified the contribution of each process to the polarization was set up, allowing the study of the contributions as a snapshot in time and as an average over a cycle. Mass transport in electrolyte was shown to be a crucial feature to improve especially if the battery is expected to undergo high current-loads for long periods of time.

Safety-concerns when a battery cell is short-circuited were investigated for three types of short-circuit scenarios. All scenarios raised the temperature to the point where exothermic side reactions were initiated. The similarities between the scenarios in temperature increase were a result of the limiting current being reached. The differences, however small, were related to the placement of the short-circuit. Especially when the current collectors were not directly connected by the short circuit, an increased electronic resistance was observed which lowered both the generated current and heat.

The aging of a battery cell was investigated by model analysis of electrodes harvested from fresh and aged cells. A methodology was used where a frequency-dependent model was fitted to three-electrode impedance experiments by tuning parameters associated to electrode degradation. For cycled cells, electrolyte decomposition products inhibiting the mass transport in the electrolyte and particle cracking in the positive electrode increased the impedance. A similar model was also set up for investigation of the lithium intercalation processes in PAN-based carbon fibers, showing it to have both good mass transport and kinetic capabilities.

Abstract [sv]

Laddningsbara litiumjonbatterier har både ur energi- och effektsynpunkt möjligheten att kunna användas i elhybridfordon och inom andra effektkrävande tillämpningsområden. Batteriets säkerhet och livslängd är dock inte helt tillförlitliga. Dessutom finns det fortfarande utrymme för förbättringar av litiumjonbatteriets prestanda.

I det här arbetet har matematiska modeller baserade på fysikaliska egenskaper framgångsrikt ställts upp och lösts numeriskt för att studera prestandan, säkerheten samt åldrandet hos litiumjonbatterisystem. Denna typ av modellering gjorde det möjligt att detaljerat analysera hur de elektrokemiska processerna bidrar. Eftersom modellerna omfattade ett stort antal parametrar och har variabler som förändras i åtminstone en dimension med tid eller frekvens, krävdes det att tydliga strategier för arbetet ställdes upp. Modelleringsstudiens noggrannhet stärktes av att flertalet av de använda parametrarna hade bestämts experimentellt.

Polarisationen som ett mått på prestanda bestämdes för ett effektoptimerat batteri under olika laster. En metodik som separerar och beräknar hur mycket varje process bidrar till polarisationen skapades och användes för att studera bidragen över tid eller över en hel lastcykel. Resultaten visade att masstransporten i elektrolyten påverkar till stor del och bör förbättras om batteriet förväntas belastas med hög ström under lång tid.

Säkerheten i samband med kortslutning av en battericell undersöktes för tre olika fall av kortslutningar. Alla fall uppvisade en temperaturökning som skulle kunna bidra till att exoterma reaktioner startas och termisk rusning uppstår. Temperaturökningen var liknande i samtliga kortslutningsfall och berodde på att gränsströmmen nåddes inom cellen. Skillnaderna mellan kortslutningsfallen var inte så betydande men kunde härledas till kortslutningens placering. Framförallt fallet då strömtilledarna inte kontakterades av kortslutningen observerades en ökad elektronisk resistans som sänkte både strömmen och värmeproduktionen.

Åldringen i en battericell undersöktes genom modellanalys av elektroder som tagits från nya eller åldrade celler. Som metod användes en frekvensberoende modell som anpassades till tre-elektrod-impedansmätningar genom förändring av parametrar som beskriver elektrodnedbrytning. Då cellerna cyklats, visade förändringen av dessa parametrar att impedansen ökar på grund av nedbrytningsprodukter från elektrolyten som hindrar masstransporten och att det aktiva materialet i positiva elektroden spricker. En liknande modell användes också till att undersöka PAN-baserade kolfibrers förmåga att interkalera litium och resultaten visade på att den har mycket goda elektrokemiska egenskaper.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 66 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:25
Keyword
lithium-ion battery, modeling, electrochemical processes, impedance, polarization, performance, safety, aging, power optimized battery, litiumjonbatteri, modellering, elektrokemiska processer, impedans, polarisation, prestanda, säkerhet, åldring, effektoptimerat batteri
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-122308 (URN)978-91-7501-745-7 (ISBN)
Public defence
2013-06-10, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
The Swedish Energy Agency
Note

QC 20130520

Available from: 2013-05-20 Created: 2013-05-17 Last updated: 2013-05-20Bibliographically approved
2. Performance of Conventional and Structural Lithium-Ion Batteries
Open this publication in new window or tab >>Performance of Conventional and Structural Lithium-Ion Batteries
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries have, in recent years, experienced a rapid development from small everyday devices towards hybrid electric vehicle (HEV) applications. Due to this shift in application area, the battery performance andits degradation with time are becoming increasingly important issues to besolved.In this thesis, lithium-ion batteries are investigated with focus on lifetime performance of an existing battery chemistry, and development of electrodes for so-called structural batteries. The systems are evaluated by electrochemical methods, such as cycling and electrochemical impedance spectroscopy (EIS),combined with material characterization and modeling.

Lifetime performance of mesocarbon microbeads (MCMB)/LiFePO4 cells was investigated to develop an understanding of how this technology tolerates and is influenced by different conditions, such as cycling, storage and temperature.The lifetime of the LiFePO4-based cells was found to be significantly reduced by cycling at elevated temperature, almost five times shorter compared to cycle-aged cells at ambient temperature. The calendar-aged cells also showed major signs of degradation at elevated temperatures. The overall cause of aging was electrolyte decomposition which resulted in loss of cyclable lithium, i.e. capacity fade, and impedance increase.

Commercially available polyacrylonitrile (PAN)-based carbon fibers were investigated, both electrochemically and mechanically, to determine their suitability as negative electrodes in structural batteries. The electrochemical performance of carbon fibers was found to be excellent compared to other negative electrode materials, especially for single or well-separated fibers. The mechanical properties, measured as changes in the tensile properties, showed that the tensile stiffness was unaffected by lithium-ion intercalation and cycling. The ultimate tensile strength, however, showed a distinct variation with state-of-charge (SOC). Overall, carbon fibers are suitable for structural battery applications.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 48 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:28
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-122875 (URN)978-91-7501-774-7 (ISBN)
Public defence
2013-06-12, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130529

Available from: 2013-05-29 Created: 2013-05-28 Last updated: 2013-05-29Bibliographically approved

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