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Structural Changes in Lithium Battery Materials Induced by Aging or Usage
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Li-ion batteries have a huge potential for use in electrification of the transportation sector. The major challenge to be met is the limited energy storage capacity of the battery pack: both the amount of energy which can be stored within the space available in the vehicle (defining its range), and the aging of the individual battery cells (determining how long a whole pack can deliver sufficient energy and power to drive the vehicle). This thesis aims to increase our knowledge and understanding of structural changes induced by aging and usage of the Li-ion battery materials involved.

Aging processes have been studied in commercial-size Li-ion cells with two different chemistries. LiFePO4/graphite cells were aged under different conditions, and thereafter examined at different points along the electrodes by post mortem characterisation using SEM, XPS, XRD and electrochemical characterization in half-cells. The results revealed large differences in degradation behaviour under different aging conditions and in different regions of the same cell. The aging of LiMn2O4-LiCoO2/Li4Ti5O12 cells was studied under two different aging conditions. Post mortem analysis revealed a high degree of Mn/Co mixing within individual particles of the LiMn2O4-LiCoO2 composite electrode.

Structural changes induced by lithium insertion were studied in two negative electrode materials: in Li0.5Ni0.25TiOPO4 using in situ XRD, and in Ni0.5TiOPO4 using EXAFS, XANES and HAXPES. It was shown that Li0.5Ni0.25TiOPO4 lost most of its long-range-order during lithiation, and that both Ni and Ti were involved in the charge compensation mechanism during lithiation/delithiation of Ni0.5TiOPO4, with small clusters of metal-like Ni forming during lithiation.

Finally, in situ XRD studies were also made of the reaction pathways to form LiFeSO4F from two sets of reactants: either FeSO4·H2O and LiF, or Li2SO4 and FeF2. During the heat treatment, Li2SO4 and FeF2 react to form FeSO4·H2O and LiF in a first step. In a second step LiFeSO4F is formed. This underlines the importance of the structural similarities between LiFeSO4F and FeSO4·H2O in the formation process of LiFeSO4F.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 75 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1227
Keyword [en]
Li-ion batteries, XRD, EXAFS, HAXPES
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-243328ISBN: 978-91-554-9165-9 (print)OAI: oai:DiVA.org:uu-243328DiVA: diva2:787036
Public defence
2015-03-27, Å4001, Ångström laboratory, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2015-03-04 Created: 2015-02-09 Last updated: 2015-03-12Bibliographically approved
List of papers
1. Analysis of aging of commercial composite metal oxide - Li4Ti5O12 battery cells
Open this publication in new window or tab >>Analysis of aging of commercial composite metal oxide - Li4Ti5O12 battery cells
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2014 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 270, 131-141 p.Article in journal (Refereed) Published
Abstract [en]

Commercial battery cells with Li4Ti5O12 negative electrode and composite metal oxide positive electrode have been analyzed with respect to aging mechanisms. Electrochemical impedance spectroscopy (EIS), differential capacity analysis (dQ/dV), differential voltage analysis (dV/dQ) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) were used to identify different ageing mechanisms such as lithium inventory loss, loss of active electrode material and surface film growth. The active material of the positive electrode was also examined by X-ray diffraction (XRD). Aging mechanisms were studied for both calendar-aged and cycle-aged cells. Data from half cells prepared from post mortem harvested electrode material, using lithium foil as negative electrode and pouch material as encapsulation, were used as reference to full cell data. Electrochemical analysis of full and half cells combined with material analysis showed to be a powerful method to identify aging mechanisms in this type of commercial cells. The calendar-aged cell showed insignificant aging while the cycle-aged cell showed noticeable loss of positive electrode active material and loss of cyclable lithium, but only minor loss of negative electrode active material. The results imply that Li4Ti5O12 negative electrode material is a good alternative to other materials if high energy density is not the primary goal.

Keyword
Hybrid electrical vehicle (HEV), Lithium ion battery, Li4Ti5O12, LiMn2O4, dV/dQ, dQ/dV
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-235294 (URN)10.1016/j.jpowsour.2014.07.050 (DOI)000342245400017 ()
Available from: 2014-11-11 Created: 2014-10-30 Last updated: 2017-12-05Bibliographically approved
2. Non-uniform aging of cycled commercial LiFePO4//graphite cylindrical cells revealed by post-mortem analysis
Open this publication in new window or tab >>Non-uniform aging of cycled commercial LiFePO4//graphite cylindrical cells revealed by post-mortem analysis
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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.

Keyword
Battery aging, LiFePO4/graphite cells, Hybrid electric vehicle, Synchrotron material characterization, Electrode utilization
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-224557 (URN)10.1016/j.jpowsour.2014.01.105 (DOI)000333780000017 ()
Available from: 2014-05-19 Created: 2014-05-14 Last updated: 2017-12-05Bibliographically approved
3. Electrochemical lithium ion intercalation in Li 0.5Ni 0.25TiOPO 4 examined by in situ X-ray diffraction
Open this publication in new window or tab >>Electrochemical lithium ion intercalation in Li 0.5Ni 0.25TiOPO 4 examined by in situ X-ray diffraction
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2012 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 225, no SI, 547-550 p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

The complex structural transformations of Li 0.5Ni 0.25TiOPO 4 during electrochemical lithiation have been examined by in situ X-ray diffraction. During the first lithiation two structural changes take place: first a transition to a second monoclinic phase (a = 9.085(4), b = 8.414(5), c = 6.886(5), β = 99.85(4)) and secondly a transition to a third phase with limited long-range order. The third phase is held together by a network of corner sharing Ti-O octahedra and phosphate ions with disordered Ni-Li channels. During delithiation the third phase is partially transformed back to a slightly disordered original phase, Li 0.5Ni 0.25TiOPO 4 without formation of the second intermediate phase. These phase transitions correspond well to the different voltage plateaus that this material shows during electrochemical cycling.

Keyword
Batteries, In situ X-ray powder diffraction, Lithium intercalation compounds, Corner sharing, De-lithiation, Electrochemical cycling, Electrochemical lithiation, In-situ, Intermediate phase, Lithiation, Lithium Intercalation, Lithium ions, Long range orders, Monoclinic phase, Phosphate ions, Structural change, Structural transformation, Third phase, Solar cells, X ray diffraction, X ray powder diffraction, Lithium
National Category
Natural Sciences Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-186837 (URN)10.1016/j.ssi.2011.11.001 (DOI)000311873400113 ()
Conference
18th International Conference on Solid State Ionics, July 3 -8, 2011, Warsaw, Poland
Funder
StandUp
Available from: 2012-12-06 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
4. Electronic and Structural Changes in Ni0.5TiOPO4 Li-ion Battery Cells Upon First Lithiation and Delithiation, Studied by High-Energy X-ray Spectroscopies
Open this publication in new window or tab >>Electronic and Structural Changes in Ni0.5TiOPO4 Li-ion Battery Cells Upon First Lithiation and Delithiation, Studied by High-Energy X-ray Spectroscopies
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2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 18, 9692-9704 p.Article in journal (Refereed) Published
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-243325 (URN)10.1021/jp511170m (DOI)000354339000002 ()
Available from: 2015-02-08 Created: 2015-02-08 Last updated: 2017-12-04Bibliographically approved
5. Formation of Tavorite-Type LiFeSO4F Followed by In Situ X-ray Diffraction
Open this publication in new window or tab >>Formation of Tavorite-Type LiFeSO4F Followed by In Situ X-ray Diffraction
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2015 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 298, 363-368 p.Article in journal (Refereed) Published
Abstract [en]

The tavorite-type polymorph of LiFeSO4F has recently attracted substantial attention as a positive elec- trode material for lithium ion batteries. The synthesis of this material is generally considered to rely on a topotactic exchange of water (H2O) for lithium (Li) and fluorine (F) within the structurally similar hy- drated iron sulfate precursor (FeSO4·H2O) when reacted with lithium fluoride (LiF). However, there have also been discussions in the literature regarding the possibility of a non-topotactic reaction mechanism between lithium sulfate (Li2SO4) and iron fluoride (FeF2) in tetraethylene glycol (TEG) as reaction medium. In this work, we use in situ X-ray diffraction to continuously follow the formation of LiFeSO4F from the two suggested precursor mixtures in a setup aimed to mimic the conditions of a solvothermal autoclave synthesis. It is demonstrated that LiFeSO4F is formed directly from FeSO4·H2O and LiF, in agreement with the proposed topotactic mechanism. The Li2SO4 and FeF2 precursors, on the other hand, are shown to rapidly transform into FeSO4·H2O and LiF with the water originating from the highly hygroscopic TEG before a subsequent formation of LiFeSO4F is initiated. The results highlight the importance of the FeSO4·H2O precursor in obtaining the tavorite-type LiFeSO4F, as it is observed in both reaction routes.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-243324 (URN)10.1016/j.jpowsour.2015.08.062 (DOI)000362146800044 ()
Funder
VINNOVA, P37446-1Swedish Energy Agency, 30769-2Swedish Research Council, C0468101StandUp
Available from: 2015-02-08 Created: 2015-02-08 Last updated: 2017-12-04Bibliographically approved

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