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Electrochemical characterisation and modelling of the mass transport phenomena in LiPF6-EC-EMC electrolyte
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.ORCID-id: 0000-0002-9392-9059
KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.ORCID-id: 0000-0001-9203-9313
2008 (engelsk)Inngår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 53, nr 22, s. 6356-6365Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The conductivity, the salt diffusion coefficient, the lithium-ion transport number and the thermodynamic factor of the salt and the solvent were reported for LiPF6 in EC:EMC (3:7) at 25 IC and for concentrations between 0.2 and 2.0 mol/d M3. The mass transport in the electrolyte was fully characterised by combining three types of electrochemical experiments; concentration cells, galvanostatic polarisation experiments and electrochemical impedance measurements with a mathematical description of the mass transport in the electrolyte. The apparent salt diffusion coefficient had a local maximum in the concentration range, while the viscosity-dependent salt diffusion coefficient decreased from 4.1 X 10-10 M2/s at 0.2 mol/d M3 to 4.4 x 10-11 M2/s at 2.0 mol/dM3. Both the thermodynamic factor and the conductivity varied strongly with the concentration. The conductivity had a maximum of 9.5 mS/cm at 1.0 mol/dm 3. The lithium-ion transport numberwith respect to the room decreased with increasing salt concentration, with a maximum of 0.37 at 0.2 molldm 3 in the concentration range. The Maxwell-Stefan diffusivities and the electrolyte potential drop in a lithium-ion battery at steady state were lastly calculated from the obtained transport properties. An analysis of the characterisation method was also done on the basis of the characterisation results.

sted, utgiver, år, opplag, sider
2008. Vol. 53, nr 22, s. 6356-6365
Emneord [en]
Li-ion battery, lithium hexafluorophosphate, Maxwell-Stefan equation, transport properties, characterisation, li-ion battery, polymer electrolyte, diffusion, polarization, carbonate
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-17731DOI: 10.1016/j.electacta.2008.04.023ISI: 000258009800010Scopus ID: 2-s2.0-54249111513OAI: oai:DiVA.org:kth-17731DiVA, id: diva2:335776
Merknad
QC 20100525Tilgjengelig fra: 2010-08-05 Laget: 2010-08-05 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. An Experimental and Theoretical Study of the Mass Transport in Lithium-Ion Battery Electrolytes
Åpne denne publikasjonen i ny fane eller vindu >>An Experimental and Theoretical Study of the Mass Transport in Lithium-Ion Battery Electrolytes
2011 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Lithium‐ion batteries are particularly suitable as energy storage solutions in high power applications, such as hybrid electric vehicles. It is generally considered that one of the processes that limit the power density for lithium‐ion batteries is the mass transport in the electrolyte. Yet, it is still difficult to find a set of properties that fully describe the mass transport for the most common electrolytes. In this work, characterization studies of the mass transport were undertaken for two technically important lithium‐ion battery electrolytes: (1) a liquid electrolyte which consist of LiPF6 dissolved in ethyl methyl carbonate (EMC) and ethylene carbonate (EC) and, (2) a gel electrolyte which consists of LiPF6 dissolved in ethylene carbonate, propylene carbonate (PC) and poly(vinylidenefluoride‐hexafluoropropylene) (P(VdFHFP)).The mass transport in the electrolytes was characterized by combining several experiments. The Maxwell‐Stefan equation was used as basis for the characterization. Models of the transport were formulated from the equation and the apparent transport properties were identified. The characterization methods were first analyzed mathematically in order to establish at which conditions the characterization experiments should be performed. The values of the apparent transport properties were then obtained by optimizing the models to the experimental responses. In order to give the characterization results a comprehensible interpretation and to allow benchmarking of electrolytes, the concept of a normalized potential gradient was introduced.The characterization results of the liquid electrolyte were used in a full cell model of a LiNi0.8Co0.15Al0.05O2 | LiPF6 EC:EMC (3:7) | MAG‐10 cell. The model was developed to analyze the mass transport during a hybrid pulse power characterization (HPPC) test. The analysis was made with a method where the polarization was split up into parts each associated with a process within the cell. The optimum composition in terms of mass transport was found to lie between 0.5 and 1.2 mol/dm3 LiPF6 for the liquid electrolyte and between 5 and 7 wt. % LiPF6 for the gel electrolyte. Less amount of polymer in the gel electrolyte gave a faster mass transport. It was also found that the mass transport in the liquid electrolyte contributed to a major part of the polarization during HPPC tests.

Abstract [sv]

Litiumjonbatterier är speciellt lämpliga som ackumulatorer i högeffektsapplikationer som elhybridfordon. Det är idag allmänt accepterat att en av processerna som begränsar effekttätheten för litiumjonbatterier är masstransporten i elektrolyten. Trots detta är det fortfarande svårt att få tag på data som fullständigt beskriver masstransporten i de vanligaste elektrolyterna.

I det här arbetet har masstransportkarakteriseringar gjorts för två tekniskt viktiga elektrolyter: (1) en vätskeelektrolyt som består av LiPF6 upplöst i etylenkarbonat (EC) och etylmetylkarbonat (EMC), och (2) en gel elektrolyt som består av LiPF6 upplöst i EC, propylenkarbonat (PC) och poly(vinylidene fluoride‐hexafluoro propylene) (P(VdFHFP)).

Masstransporten i elektrolyterna karakteriserades genom att kombinera ett antal karakteriseringsexperiment. Maxwell‐Stefans ekvation användes som utgångspunkt i karakteriseringarna. Modeller av transporten formulerades från ekvationen och de effektiva transportegenskaperna identifierades. En matematisk analys gjordes först av karakteriseringstekniken, så att det kunde fastslås för vilka förhållanden experimenten skulle utföras. Värderna av transportegenskaperna erhölls genom att optimera modellerna till det experimentella beteendet. För att ge karakteriseringsresultaten en begriplig tolkning och för att kunna mäta prestandan av elektrolyter, infördes konceptet normaliserad potentialgradient.

Resultatet från karakteriseringen av vätskeelektrolyten användes i en model av en LiNi0.8Co0.15Al0.05O2 | LiPF6 EC:EMC (3:7) | MAG‐10 cell. Modellen utvecklades för att analysera masstransporten i cellen under ett hybridpulstest (HPPC). Analysen gjordes med en metod där polarisationen delades upp i delar som var och en var kopplad till en process i batteriet.

Den optimala sammansättningen med avseende på masstransporten låg i regionen 0.5–1.2 mol/dm3 LiPF6 för vätskeelektrolyten och 5‐7 vikt% LiPF6 för gelelektrolyten. Mindre mängd polymer i gelelektrolyten gav en snabbare masstransport. Det konstaterades också att masstransporten i vätskeelektrolyten bidrog med en av de största delarna till polarisationen i HPPC testen.

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2011. s. 64
Serie
Trita-CHE-Report, ISSN 1654-1081 ; 2011:6
Emneord
Lithium‐ion batteries, Electrolytes, Transport properties, Conductivity, Diffusion coefficients, Transport number, Maxwell-Stefan equation, Simulations, Mathematical analysis, Polarization, Hybrid electric vehicles, Litiumjonbatterier, Aprotiska elektrolyter, Transport egenskaper, Konduktivitet, Diffusion koefficienter, Transporttal, Maxwell-Stefans ekvation, Simuleringar, Matematisk analys, Polarisation, Elhybridfordon
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-29121 (URN)978-91-7415-852-6 (ISBN)
Disputas
2011-02-28, K2, Teknikringen 28, Entréplan, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad
QC 20110128Tilgjengelig fra: 2011-01-28 Laget: 2011-01-25 Sist oppdatert: 2011-05-20bibliografisk kontrollert

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