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Manganese in the SEI layer of Li4Ti5O12 studied using combined NEXAFS and HAXPES techniques
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. (Kristina Edström)
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0003-2538-8104
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
Helmholz Zentrum Berlin Mat & Energie GmbH, D-14109 Berlin, Germany.
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2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 6, 3206-3213 p.Article in journal (Refereed) Published
Abstract [en]

A combination of hard X-ray photoelectron spectroscopy (HAXPES) and near edge X-ray absorption fine structure (NEXAFS) are here used to investigate the presence and chemical state of crossover manganese deposited on Li-ion battery anodes. The synchrotron based experimental techniques-using HAXPES and NEXAFS analysis on the same sample in one analysis chamber-enabled us to acquire complementary sets of information. The Mn crossover and its influence on the anode interfacial chemistry has been a topic of controversy in the literature. Cells comprising lithium manganese oxide (LiMn2O4, LMO) cathodes and lithium titanate (Li4Ti5O12, LTO) anodes were investigated using LP40 (1 M LiPF6, EC:DEC 1:1) electrolyte. LTO electrodes at lithiated, delithiated, and open circuit voltage (OCV-stored) states were analyzed to investigate the potential dependency of the manganese oxidation state. It was primarily found that a solid surface layer was formed on the LTO electrode and that this layer contains deposited Mn from the cathode. The results revealed that manganese is present in the ionic state, independent of the lithiation of the LTO electrode. The chemical environment of the deposited manganese could not be assigned to simple compounds such as fluorides or oxides, indicating that the state of manganese is in a more complex form.

Place, publisher, year, edition, pages
2016. Vol. 120, no 6, 3206-3213 p.
National Category
Other Chemical Engineering
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-267788DOI: 10.1021/acs.jpcc.5b11756ISI: 000370678700012OAI: oai:DiVA.org:uu-267788DiVA: diva2:874308
Funder
Swedish Energy Agency
Available from: 2015-11-26 Created: 2015-11-26 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Lithium titanate as anode material in lithium-ion batteries: -A surface study
Open this publication in new window or tab >>Lithium titanate as anode material in lithium-ion batteries: -A surface study
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The ever increasing awareness of the environment and sustainability drives research to find new solutions in every part of society. In the transport sector, this has led to a goal of replacing the internal combustion engine (ICE) with an electrical engine that can be powered by renewable electricity. As a battery for vehicles, the Li-ion chemistries have become dominant due to their superior volumetric and gravimetric energy densities. While promising, electric vehicles require further improvements in terms of capacity and power output before they can truly replace their ICE counterparts. Another aspect is the CO2 emissions over lifetime, since the electric vehicle itself presently outlives its battery, making battery replacement necessary. If the lifetime of the battery could be increased, the life-cycle emissions would be significantly lowered, making the electric vehicle an even more suitable candidate for a sustainable society. In this context, lithium titanium oxide (LTO) has been suggested as a new anode material in heavy electric vehicles applications due to intrinsic properties regarding safety, lifetime and availability. The LTO battery chemistry is, however, not fully understood and fundamental research is necessary for future improvements. The scope of this project is to investigate degradation mechanisms in LTO-based batteries to be able to mitigate these and prolong the device lifetime so that, in the end, a suitable chemistry for large scale applications can be suggested. The work presented in this licentiate thesis is focused on the LTO electrode/electrolyte interface. Photoelectron spectroscopy (PES) was applied to determine whether the usage of LTO would prevent anode-side electrolyte decomposition, as suggested from the intercalation potential being inside the electrochemical stability window of common electrolytes. It has been found that electrolyte decomposition indeed occurs, with mostly hydrocarbons of ethers, carboxylates, and some inorganic lithium fluoride as decomposition products, and that this decomposition to some extent ensued irrespective of electrochemical battery operation activity. Second, an investigation into how crossover of manganese ions from Mn-based cathodes influences this interfacial layer has been conducted. It was found, using a combination of high-energy x-ray photoelectron spectroscopy (HAXPES) and near-edge x-ray absorption fine structure (NEXAFS) that although manganese is present on the LTO anode surface when paired with a common manganese oxide spinel cathode, the manganese does little to alter the surface chemistry of the LTO electrode.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2015. 46 p.
Keyword
titanate battery anode SEI
National Category
Other Chemical Engineering
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-267567 (URN)
Presentation
2015-12-17, Beurlingrummet, Lägerhydsvägen 1, Uppsala, 13:59 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Available from: 2015-11-26 Created: 2015-11-24 Last updated: 2015-11-26Bibliographically approved
2. A Quest for the Unseen: Surface Layer Formation on Li4Ti5O12 Li-Ion Battery Anodes
Open this publication in new window or tab >>A Quest for the Unseen: Surface Layer Formation on Li4Ti5O12 Li-Ion Battery Anodes
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The electric vehicle itself today outlives its battery, necessitating battery replacement. Lithium titanium oxide (LTO) has, in this context, been suggested as a new anode material in heavy electric vehicle applications due to intrinsic properties regarding safety, lifetime and availability.

The work presented here is focused on the LTO electrode/electrolyte interface. Photoelectron spectroscopy (PES) has been applied to determine how and if the usage of LTO could prevent extensive anode-side electrolyte decomposition and build-up of a surface layer. The presence of a solid electrolyte interphase (SEI) comprising LiF, carbonates and ether compounds was found in half-cells utilizing a standard ethylene:diethylcarbonate electrolyte with 1 M LiPF6. Via testing of symmetrical LTO-LTO cells, the stability of the formed SEI was put in to question. Moreover, the traditional polyvinylidene difluoride (PVdF) binder was replaced by more environmentally benign carboxylmethyl cellulose (CMC) and polyacrilic acid (PAA) binders in LTO electrodes, and it was found that CMC helped to form a more stable surface-layer that proved beneficial for long term cycling.

Following the half-cell studies, full-cells were investigated to observe how different cathodes influence the SEI of LTO. The SEI in full-cells displayed characteristics similar to the half-cells, however, when utilizing a high voltage LiNi0.5Mn1.5O4 cathode, more electrolyte decomposition could be observed. Increasing the operational temperature of this battery cell generated even more degradation products on the LTO electrodes. Mn was also found on the anode when using Mn-based cathodes, however, it was found in its ionic state and did not significantly affect the composition or behavior of the observed SEI layer. Furthermore, by exchanging the electrolyte solvent for propylene carbonate, the thickness of the SEI increased, and by replacing the LiPF6 salt for LiBF4 the stability of the SEI improved. Thus is it demonstrated that such a passivation can be beneficial for the long-term surface stability of the electrode. These findings can therefore help prolong the lifetime of LTO-based battery chemistries.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2017. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1576
Keyword
SEI, LTO, XPS, PES, Surface Layer, Titanate
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-331349 (URN)978-91-513-0105-1 (ISBN)
Public defence
2017-12-01, Häggsalen, Ångström, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-11-10 Created: 2017-10-13 Last updated: 2017-11-10

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Nordh, TimYounesi, RezaHahlin, MariaTengstedt, CarlBrandell, DanielEdström, Kristina

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