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Non-uniform aging of cycled commercial LiFePO4//graphite cylindrical cells revealed by post-mortem analysis
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0003-4901-5820
Uppsala University.
Chalmers Technical University.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0001-9559-0004
Show others and affiliations
2014 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 257, 126-137 p.Article in journal (Refereed) Published
Abstract [en]

Aging of power-optimized commercial 2.3 Ah cylindrical LiFePO4//graphite cells to be used in hybrid electric vehicle is investigated and compared for three different aging procedures; (i) using a simulated hybrid electric vehicle cycle within a narrow SOC-range, (ii) using a constant-current cycle over a 100% SOC-range, and (iii) stored during three years at 22 degrees C. Postmortem analysis of the cells is performed after full-cell electrochemical characterization and discharge. EIS and capacity measurements are made on different parts of the disassembled cells. Material characterization includes SEM, EDX, HAXPES/XPS and XRD. The most remarkable result is that both cycled cells displayed highly uneven aging primarily of the graphite electrodes, showing large differences between the central parts of the jellyroll compared to the outer parts. The aging variations are identified as differences in capacity and impedance of the graphite electrode, associated with different SEI characteristics. Loss of cyclable lithium is mirrored by a varying degree of lithiation in the positive electrode and electrode slippage. The spatial variation in negative electrode degradation and utilization observed is most likely connected to gradients in temperature and pressure, that can give rise to current density and potential distributions within the jellyroll during cycling.

Place, publisher, year, edition, pages
2014. Vol. 257, 126-137 p.
Keyword [en]
Battery aging, LiFePO4/graphite cells, Hybrid electric vehicle, Synchrotron material characterization, Electrode utilization
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-145047DOI: 10.1016/j.jpowsour.2014.01.105ISI: 000333780000017Scopus ID: 2-s2.0-84894504735OAI: oai:DiVA.org:kth-145047DiVA: diva2:715946
Funder
Swedish Energy Agency
Note

QC 20140509

Available from: 2014-05-07 Created: 2014-05-07 Last updated: 2017-12-05Bibliographically approved
In thesis
1. 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
2. Methods for Testing and Analyzing Lithium-Ion Battery Cells intended for Heavy-Duty Hybrid Electric Vehicles
Open this publication in new window or tab >>Methods for Testing and Analyzing Lithium-Ion Battery Cells intended for Heavy-Duty Hybrid Electric Vehicles
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries designed for use in heavy-duty hybrid vehicles are continuously improved in terms of performance and longevity, but they still have limitations that need to be considered when developing new hybrid vehicles.               

The aim of this thesis has been to study and evaluate potential test and analysis methods suitable for being used in the design process when maximizing lifetime and utilization of batteries in heavy-duty hybrid vehicles.

A concept for battery cell cycling on vehicles has been evaluated. The work included development of test equipment, verification of hardware and software as well as an extended period of validation on heavy-duty trucks. The work showed that the concept has great potential for evaluating strategies for battery usage in hybrid vehicles, but is less useful for accelerated aging of battery cells.                            

Battery cells encapsulated in flexible packaging material have been investigated with respect to the durability of the encapsulation in a demanding heavy-duty hybrid truck environment. No effect on water intrusion was detected after vibration and temperature cycling of the battery cells.                   

Aging of commercial battery cells of the type lithium manganese oxide - lithium cobalt oxide / lithium titanium oxide (LMO-LCO/LTO) was investigated with different electrochemical methods to gain a deeper understanding of the origin of performance deterioration, and to understand the consequences of aging from a vehicle manufacturer's perspective. The investigation revealed that both capacity loss and impedance rise were largely linked to the positive electrode for this type of battery chemistry.                          

Postmortem analysis of material from cycle-aged and calendar-aged battery cells of the type LMO-LCO/LTO and LiFePO4/graphite was performed to reveal details about aging mechanisms for those cell chemistries. Analysis of cycle-aged LMO-LCO/LTO cells revealed traces of manganese in the negative electrode and that the positive electrode exhibited the most severe aging. Analysis of cycle-aged LFP/graphite cells revealed traces of iron in the negative electrode and that the negative electrode exhibited the most severe aging.

Abstract [sv]

Litiumjonbatterier anpassade för användning i tunga hybridfordon förbättras kontinuerligt med avseende på prestanda och livslängd men har fortfarande begränsningar som måste beaktas vid utveckling av nya hybridfordon.                

Syftet med denna avhandling har varit att studera och utvärdera potentiella prov- och analysmetoder lämpliga för användning i arbetet med att maximera livslängd och utnyttjandegrad av batterier i tunga hybridfordon.                              

Ett koncept för battericykling på fordon har utvärderats. Arbetet innefattade utveckling av testutrustning, verifiering av hårdvara och mjukvara samt en längre periods validering på lastbilar. Arbetet har visat att konceptet har stor potential för utvärdering av strategier för användandet av batterier i hybridfordon, men är mindre användbar för åldring av batterier.                               

Batterier kapslade i flexibelt förpackningsmaterial har undersökts med avseende på kapslingens hållbarhet i en krävande hybridlastbilsmiljö. Ingen påverkan på fuktinträngning kunde påvisas efter vibration och temperaturcykling av de testade battericellerna.                    

Åldring av kommersiella battericeller av typen litiummanganoxid - litiumkoboltoxid/litiumtitanoxid (LMO-LCO/LTO) undersöktes med olika elektrokemiska metoder för att få en djupare förståelse för prestandaförändringens ursprung och för att förstå konsekvenserna av åldrandet ur en fordonstillverkares användarperspektiv. Undersökningen visade att både kapacitetsförlust och impedanshöjning till största delen var kopplat till den positiva elektroden för denna batterityp.                 

Post-mortem analys av material från cyklade och kalenderåldrade kommersiella battericeller av typen LMO-LCO/LTO och LiFePO4/grafit utfördes för att avslöja detaljer kring åldringsmekanismerna för dessa cellkemier. Vid analys av cyklade LMO-LCO/LTO celler påvisades mangan i den negativa elektroden samt uppvisade den positiva elektroden kraftigast åldring. Vid analys av cyklade LFP/grafit celler påvisades järn i den negativa elektroden samt uppvisade den negativa elektroden kraftigast åldring.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xii, 75 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:21
Keyword
Li-ion, battery, hybrid electric vehicle
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-145166 (URN)978-91-7595-127-0 (ISBN)
Public defence
2014-06-03, K2, Teknikringen 28, KTH, Stockholm, 16:06 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 35088-1
Note

QC 20140520

Available from: 2014-05-20 Created: 2014-05-13 Last updated: 2014-06-03Bibliographically approved

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Klett, MatildaSvens, PontusWreland Lindström, RakelLindbergh, Göran

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