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Lithium titanate as anode material in lithium-ion batteries: -A surface study
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. (Kristina Edström)
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 [en]
titanate battery anode SEI
National Category
Other Chemical Engineering
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-267567OAI: oai:DiVA.org:uu-267567DiVA: diva2:873630
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
List of papers
1. Depth profiling the solid electrolyte interpahase on lithium titanate (Li4Ti5O12) using synchrotron-based photoelectron spectroscopy
Open this publication in new window or tab >>Depth profiling the solid electrolyte interpahase on lithium titanate (Li4Ti5O12) using synchrotron-based photoelectron spectroscopy
2015 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 294, 173-179 p.Article in journal (Refereed) Published
Abstract [en]

The presence of a surface layer on lithium titanate (Li4Ti6O12, LTO) anodes, which has been a topic of debate in scientific literature, is here investigated with tunable high surface sensitive synchrotron-based photoelectron spectroscopy (PES) to obtain a reliable depth profile of the interphase. Li vertical bar vertical bar LTO cells with electrolytes consisting of 1 M lithium hexafluorophosphate dissolved in ethylene carbonate:diethyl carbonate (LiPF6 in EC:DEC) were cycled in two different voltage windows of 1.0-2.0 V and 1.4-2.0 V. LTO electrodes were characterized after 5 and 100 cycles. Also the pristine electrode as such, and an electrode soaked in the electrolyte were analyzed by varying the photon energies enabling depth profiling of the outermost surface layer. The main components of the surface layer were found to be ethers, P-O containing compounds, and lithium fluoride.

Keyword
Li-ion batteries, LTO, PES, XPS, Surface layer, SEI
National Category
Energy Engineering Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-261214 (URN)10.1016/j.jpowsour.2015.06.038 (DOI)000358968400022 ()
Funder
Swedish Energy Agency
Available from: 2015-09-08 Created: 2015-08-31 Last updated: 2017-12-04Bibliographically approved
2. Manganese in the SEI layer of Li4Ti5O12 studied using combined NEXAFS and HAXPES techniques
Open this publication in new window or tab >>Manganese in the SEI layer of Li4Ti5O12 studied using combined NEXAFS and HAXPES techniques
Show others...
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.

National Category
Other Chemical Engineering
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-267788 (URN)10.1021/acs.jpcc.5b11756 (DOI)000370678700012 ()
Funder
Swedish Energy Agency
Available from: 2015-11-26 Created: 2015-11-26 Last updated: 2017-12-01Bibliographically approved

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