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Iron based Li-ion insertion materials for battery applications
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala universitet. (Ångström Advanced Battery Center)
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Li-ion batteries are currently the most efficient technology available for electrochemical energy storage. The technology has revolutionized the portable electronics market and is becoming a corner stone for large scale applications, such as electric vehicles. It is therefore important to develop materials in which the energy storage relies on abundant redox active species, such as iron. In this thesis, new iron based electrode materials for positive electrodes in Li-ion batteries were investigated. Lithium iron pyrophosphate (Li2FeP2O7) and two polymorphs of lithium iron sulphate fluoride (LiFeSO4F) were studied.

For Li2FeP2O7, preferred oxidation of iron with different coordination numbers within the crystal structure was studied, and six-coordinated iron was found to be oxidized preferentially at lower potentials compared to five‑coordinated iron. Electrochemical cycling resulted in structural changes of Li2FeP2O7 through an increased Li-Fe mixing in the compound, forming a metastable state during battery operation.

For tavorite LiFeSO4F, the influence of the amount of a conductive polymer (poly(3,4-ethylenedioxythiophene), or PEDOT) was studied. All the different amounts of PEDOT coating reduced the polarization significantly, but the trade-off between functionality and weight added also has to be considered. Additionally, the effect of densifying the electrodes to different degrees is reported, and was found to have a significant influence on the battery performance. Also triplite LiFeSO4F was coated with PEODT, and it was found that the electrochemical performance improved, but not to the same extent as for tavorite LiFeSO4F. The faster solid state transport of Li-ions in tavorite type LiFeSO4F possibly accounts for the difference in electrochemical performance.

Together, the results presented herein should be of importance for developing new iron based materials for Li-ion batteries.

Abstract [sv]

Av de idag tillgängliga teknologierna för elektrokemisk energilagring så har litium-jonbatterier de bästa egenskaperna när det gäller energiförluster och energilagringskapacitet. De har revolutionerat marknaden för portabel elektronik (telefoner, laptops etc.), och blir mer och mer viktiga för storskaliga tillämpningar såsom elbilar. För den typen av applikationer måste teknologin baseras på vanligt förekommande material och grundämnen, t.ex. järn.

I den här avhandlingen har järnbaserade material för den positiva elektroden hos litium-jonbatterier studerats. Olika aspekter som påverkar spänningen och effektiviteten hos elektroderna har undersökts. Ett exempel på det är hur olika omgivningar kring järnatomerna i en förening påverkar spänningen hos ett batteri. För föreningen litiumjärnpyrofosfat visade det sig att sex närmaste grannar ger lägre spänning än fem närmaste grannar till järn. Dessutom har förändringar i föreningens struktur studerats då den används i ett batteri. Den här typen av grundforskning är viktig för förståelsen av nya elektrodmaterial i Li-jonbatterier.

Ur en mer praktisk synvinkel så har elektroder baserade på en annan järnförening, litiumjärnsulfatfluorid, utvecklats. Ledningsförmågan hos dessa elektroder har förbättrats genom att belägga föreningen med ett ledande skikt, samt att mekaniskt pressa samman elektroderna genom mangling. Båda metoderna är viktiga för att tillverka välfungerande elektroder. Föreningen litiumjärnsulfatfluorid förekommer i två olika former, och en jämförelse av hur elektriskt ledande beläggningar påverkar de bägge materialen har också gjorts i den här avhandlingen.

Tillsammans visar resultaten från de olika studierna på hur man kan arbeta och tänka kring utvecklingen av nya material för litium-jonbatterier.  

Place, publisher, year, edition, pages
Uppsala University, Department of Chemistry - Ångström Laboratory , 2016. , 39 p.
Keyword [en]
Li-ion, battery, Li2FeP2O7, LiFeSO4F, PEDOT
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-281263OAI: oai:DiVA.org:uu-281263DiVA: diva2:913544
Presentation
2016-04-12, Å2005, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , EMI11-0028
Available from: 2016-03-22 Created: 2016-03-21 Last updated: 2016-03-22Bibliographically approved
List of papers
1. Structural and Electronic Changes in Li2FeP2O7 during Electrochemical Cycling
Open this publication in new window or tab >>Structural and Electronic Changes in Li2FeP2O7 during Electrochemical Cycling
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2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 11, 3801-3804 p.Article in journal (Refereed) Published
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:uu:diva-258346 (URN)10.1021/acs.chemmater.5b00440 (DOI)000356202800004 ()
Available from: 2015-07-13 Created: 2015-07-13 Last updated: 2017-12-04Bibliographically approved
2. Battery Performance of PEDOT Coated LiFeSO4F Cathodes with Controlled Porosity
Open this publication in new window or tab >>Battery Performance of PEDOT Coated LiFeSO4F Cathodes with Controlled Porosity
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(English)Manuscript (preprint) (Other academic)
Keyword
Li-ion battery, cathode material, Tavorite, LiFeSO4F, fluorosulfate, conductive coating, PEDOT, porosity, electrochemical performance
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-281262 (URN)
Funder
Swedish Foundation for Strategic Research , EM11-0028
Available from: 2016-03-21 Created: 2016-03-21 Last updated: 2016-04-05Bibliographically approved
3. Investigating the Electrochemical Performance of PEDOT-coated Triplite-type LiFeSO4F Cathode Material
Open this publication in new window or tab >>Investigating the Electrochemical Performance of PEDOT-coated Triplite-type LiFeSO4F Cathode Material
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(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-262677 (URN)
Available from: 2015-09-18 Created: 2015-09-18 Last updated: 2016-03-22

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