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Altered electrode degradation with temperature in LiFePO4/mesocarbon microbead graphite cells diagnosed with impedance spectroscopy
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.ORCID-id: 0000-0003-4901-5820
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.ORCID-id: 0000-0002-0452-0703
Vise andre og tillknytning
2014 (engelsk)Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 141, s. 173-181Artikkel i tidsskrift (Annet vitenskapelig) 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.

sted, utgiver, år, opplag, sider
2014. Vol. 141, s. 173-181
Emneord [en]
battery aging;temperature;electrode impedance;EIS modeling;LiFePO4/MCMB graphite
HSV kategori
Identifikatorer
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, id: diva2:715969
Forskningsfinansiär
Swedish Energy Agency
Merknad

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

Tilgjengelig fra: 2014-05-07 Laget: 2014-05-07 Sist oppdatert: 2017-12-05bibliografisk kontrollert
Inngår i avhandling
1. Electrochemical Studies of Aging in Lithium-Ion Batteries
Åpne denne publikasjonen i ny fane eller vindu >>Electrochemical Studies of Aging in Lithium-Ion Batteries
2014 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2014. s. x, 72
Serie
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:16
Emneord
aging, EIS modeling, electrolyte characterization, graphite, hybrid electric vehicles, impedance spectroscopy, LiFePO4, Li-ion batteries
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-145057 (URN)978-91-7595-116-4 (ISBN)
Disputas
2014-05-28, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish Energy Agency
Merknad

QC 20140512

Tilgjengelig fra: 2014-05-12 Laget: 2014-05-07 Sist oppdatert: 2017-02-22bibliografisk kontrollert

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