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Altered electrode degradation with temperature in LiFePO4/mesocarbon microbead graphite cells diagnosed with impedance spectroscopy
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.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.ORCID iD: 0000-0002-0452-0703
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2014 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 141, 173-181 p.Article in journal (Other academic) Published
Abstract [en]

Electrode degradation in LiFePO4 / mesocarbon microbead graphite (MCMB) pouch cells aged at 55 °C by a synthetic hybrid drive cycle or storage is diagnosed and put into context with previous results of aging at 22 °C. The electrode degradation is evaluated by means of electrochemical impedance spectroscopy (EIS), measured separately on electrodes harvested from the cells, and by using a physics-based impedance model for aging evaluation. Additional capacity measurements, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) are used in the evaluation. At 55 °C the LiFePO4 electrode shows increased particle/electronic conductor resistance, for both stored and cycled electrodes. This differs from results obtained at 22 °C, where the electrode suffered lowered porosity, particle fracture, and loss of active material. For graphite, only cycling gave a sustained effect on electrode performance at 55 °C due to lowered porosity and changes of surface properties, and to greater extent than at low temperature. Furthermore, increased current collector resistance also contributes to a large part of the pouch cell impedance when aged at increased temperatures. The result shows that increased temperature promotes different degradation on the electrode level, and is an important implication for high temperature accelerated aging. In light of the electrode observations, the correlation between full-cell and electrode impedances is discussed.

Place, publisher, year, edition, pages
2014. Vol. 141, 173-181 p.
Keyword [en]
battery aging;temperature;electrode impedance;EIS modeling;LiFePO4/MCMB graphite
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-145053DOI: 10.1016/j.electacta.2014.06.081ISI: 000343022900023Scopus ID: 2-s2.0-84905868311OAI: oai:DiVA.org:kth-145053DiVA: diva2:715969
Funder
Swedish Energy Agency
Note

Updated from "Manuscript" to "Journal". QC 20141112

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

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Klett, MatildaWreland Lindström, RakelBehm, MårtenLindbergh, Göran

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