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Aging in Lithium-Ion Batteries: Experimental and Model Investigation of Harvested LiFePO4 and Mesocarbon Microbead Graphite Electrodes
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: 0000-0003-4901-5820
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: 0000-0002-9392-9059
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2013 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 110, 335-348 p.Article in journal (Refereed) Published
Abstract [en]

This study investigates aging in LiFePO4/mesocarbon microbead graphite cells that have been subjected to either a synthetic hybrid drive cycle or calendar aging, at 22 C. The investigation involves detailed examination and comparison of harvested fresh and aged electrodes. The electrode properties are determined using a physics-based electrochemical impedance spectroscopy (EIS) model that is fitted to three-electrode EIS measurements, with input from measured electrode capacity and scanning electrode microscopy (SEM). Results from the model fitting provide a detailed insight to the electrode degradation and is put into context with the behavior of the full cell aging. It was established that calendar aging has negligible effect on cell impedance, while cycle aging increases the impedance mainly due to structural changes in the LiFePO4 porous electrode and electrolyte decomposition products on both electrodes. Further, full-cell capacity fade is mainly a consequence of cyclable lithium loss caused by electrolyte decomposition.

Place, publisher, year, edition, pages
2013. Vol. 110, 335-348 p.
Keyword [en]
Lithium-ion battery, Aging, EIS modeling, LiFePO4, Graphite
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-122395DOI: 10.1016/j.electacta.2013.05.081ISI: 000329530300044Scopus ID: 2-s2.0-84888320795OAI: oai:DiVA.org:kth-122395DiVA: diva2:622108
Funder
StandUpSwedish Energy Agency
Note

 QC 20140120. Updated from "Accepted" to "Published".

Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2017-12-06Bibliographically 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
3. Electrochemical Studies of Aging in Lithium-Ion Batteries
Open this publication in new window or tab >>Electrochemical Studies of Aging in Lithium-Ion Batteries
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries are today finding use in automobiles aiming at reducing fuel consumption and emissions within transportation. The requirements on batteries used in vehicles are high regarding performance and lifetime, and a better understanding of the interior processes that dictate energy and power capabilities is a key to strategic development. This thesis concerns aging in lithium-ion cells using electrochemical tools to characterize electrode and electrolyte properties that affect performance and performance loss in the cells.

 

A central difficulty regarding battery aging is to manage the coupled effects of temperature and cycling conditions on the various degradation processes that determine the lifetime of a cell. In this thesis, post-mortem analyses on harvested electrode samples from small pouch cells and larger cylindrical cells aged under different conditions form the basis of aging evaluation. The characterization is focused on electrochemical impedance spectroscopy (EIS) measurements and physics-based EIS modeling supported by several material characterization techniques to investigate degradation in terms of properties that directly affect performance. The results suggest that increased temperature alter electrode degradation and limitations relate in several cases to electrolyte transport. Variations in electrode properties sampled from different locations in the cylindrical cells show that temperature and current distributions from cycling cause uneven material utilization and aging, in several dimensions. The correlation between cell performance and localized utilization/degradation is an important aspect in meeting the challenges of battery aging in vehicle applications.

 

The use of in-situ nuclear magnetic resonance (NMR) imaging to directly capture the development of concentration gradients in a battery electrolyte during operation is successfully demonstrated. The salt diffusion coefficient and transport number for a sample electrolyte are obtained from Li+ concentration profiles using a physics-based mass-transport model. The method allows visualization of performance limitations and can be a useful tool in the study of electrochemical systems.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. x, 72 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:16
Keyword
aging, EIS modeling, electrolyte characterization, graphite, hybrid electric vehicles, impedance spectroscopy, LiFePO4, Li-ion batteries
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-145057 (URN)978-91-7595-116-4 (ISBN)
Public defence
2014-05-28, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QC 20140512

Available from: 2014-05-12 Created: 2014-05-07 Last updated: 2017-02-22Bibliographically approved

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Zavalis, Tommy GeorgiosKlett, MatildaBehm, MårtenWreland Lindström, RakelLindbergh, Göran

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