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Mathematical Models for Investigation of Performance, Safety, and Aging in Lithium-Ion Batteries
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-9698-4136
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 [en]
lithium-ion battery, modeling, electrochemical processes, impedance, polarization, performance, safety, aging, power optimized battery
Keyword [sv]
litiumjonbatteri, modellering, elektrokemiska processer, impedans, polarisation, prestanda, säkerhet, åldring, effektoptimerat batteri
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-122308ISBN: 978-91-7501-745-7 (print)OAI: oai:DiVA.org:kth-122308DiVA: diva2:621932
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
List of papers
1. Analysis of the Polarization in a Li-Ion Battery Cell by Numerical Simulations
Open this publication in new window or tab >>Analysis of the Polarization in a Li-Ion Battery Cell by Numerical Simulations
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2010 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 157, no 11, A1236-A1246 p.Article in journal (Refereed) Published
Abstract [en]

An experimentally validated model was developed to analyze the polarization of a LiNi0.8Co0.15Al0.05O2 vertical bar 1.2 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7)vertical bar MAG-10 battery cell during a hybrid pulse power characterization (HPPC) cycle. The analysis was made with a method where the polarization was split up into parts associated with activation of the electrochemical reactions, mass transport of species in the electrolyte and in the solid phase, and inadequate contact between the materials in the electrodes. Each contribution to the polarization was quantified as a snapshot in time and as an average over the HPPC cycle. The polarization during a cycle according to EUCAR was analyzed in detail for state of charge (SOC) 40 and 80. It arose mainly due to the mass transport in the electrolyte, e. g., at SOC 40 it contributed to 43% of the total polarization. In an ISO (International Organization for Standardization)-energy cycle where the current loads are higher and applied for longer times than the EUCAR cycle, the mass transport by diffusion in the electrolyte and in the solid phase of the negative electrode became more significant. The presented method offers the possibility to find a battery cell's optimal operational condition and design.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-27674 (URN)10.1149/1.3486161 (DOI)000283857900021 ()2-s2.0-77957695680 (Scopus ID)
Funder
Swedish Research CouncilStandUp
Note

QC 20150629

Available from: 2010-12-21 Created: 2010-12-20 Last updated: 2017-12-11Bibliographically approved
2. Investigation of Short-Circuit Scenarios in a Lithium-Ion Battery Cell
Open this publication in new window or tab >>Investigation of Short-Circuit Scenarios in a Lithium-Ion Battery Cell
2012 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 159, no 6, A848-A859 p.Article in journal (Refereed) Published
Abstract [en]

A short-circuited lithium-ion battery cell is likely to generate sufficient heat to initiate exothermic side reactions causing thermal runaway. A 2D coupled electrochemical-thermal model was developed to investigate a prismatic LiNi0.8Co0.15Al0.05O2 vertical bar LiPF6, EC/EMC (3:7)vertical bar MAG-10 battery cell that is short-circuited. Three short-circuit scenarios are investigated during the events from when short circuit occurs until exothermic side reactions initiate. The scenarios are an external short circuit, a nail penetration and an impurity-induced short circuit. The model is used to predict the temperature increase within the cell and to explain how the interrelation between the electrochemical processes and the thermal properties affects the increase. Important safety measures are also examined with the model. The simulation results highlight general short-circuit characteristics and critical distinctions between the scenarios. The mass transport of lithium ions in the electrolyte is found to be the most important general characteristic that determines the rate of the temperature increase. The electric resistance distinguishes the scenarios from each other. The rate of the temperature increase is dictated by the mass transport in the electrolyte even when large variations in available active material are made and it is shown to be difficult to slow down the rate by cooling.

Place, publisher, year, edition, pages
Electrochemical Society, 2012
Keyword
active material, battery cells, electrochemical process, lithium ions, lithium-ion battery, nail penetration, safety measures, short-circuit characteristics, side reactions, temperature increase, thermal runaways
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-98342 (URN)10.1149/2.096206jes (DOI)000304140700020 ()2-s2.0-84861369884 (Scopus ID)
Funder
StandUp
Note

QC 20120625

Available from: 2012-06-25 Created: 2012-06-25 Last updated: 2017-12-07Bibliographically approved
3. Aging in Lithium-Ion Batteries: Experimental and Model Investigation of Harvested LiFePO4 and Mesocarbon Microbead Graphite Electrodes
Open this publication in new window or tab >>Aging in Lithium-Ion Batteries: Experimental and Model Investigation of Harvested LiFePO4 and Mesocarbon Microbead Graphite Electrodes
Show others...
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.

Keyword
Lithium-ion battery, Aging, EIS modeling, LiFePO4, Graphite
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-122395 (URN)10.1016/j.electacta.2013.05.081 (DOI)000329530300044 ()2-s2.0-84888320795 (Scopus ID)
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
4. Characterization of Lithium Intercalation Processes of PAN-based Carbon Fibers in a Microelectrode System
Open this publication in new window or tab >>Characterization of Lithium Intercalation Processes of PAN-based Carbon Fibers in a Microelectrode System
(English)Article in journal (Other academic) Submitted
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-122398 (URN)
Funder
StandUp
Note

QC 20160622

Available from: 2013-05-20 Created: 2013-05-20 Last updated: 2016-06-22Bibliographically approved

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