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Different Shades of Li4Ti5O12 Composites: The Impact of the Binder on Interface Layer Formation
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
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2017 (English)In: ChemElectroChem, 10.1002/celc.201700395- p.Article in journal (Refereed) Published
Abstract [en]

Replacing the traditional PVdF(-HFP) electrode binder by water-soluble alternatives can potentially render electrode fabrication more environmentally benign. Herein, the surface layer formation of stored and cycled samples of two water-based Li4Ti5O12 composites employing either poly(sodium acrylate) (PAA-Na) or sodium carboxymethyl cellulose (CMC-Na) as binders are studied by X-ray photoelectron spectroscopy. In all three formulations, the surface layer composition formed upon storage differed notably from the solid-electrolyte interphase (SEI) layer formed on cycled samples. The surface layer under open-circuit conditions seems to originate mostly from the electrolyte salt (LiPF6) degradation. The comparison with cycled samples after 10 and 100 cycles shows a continuous build-up of an SEI layer on PAA-Na and PVdF-HFP electrodes. In contrast, on CMC-Na containing electrodes the SEI composition remains nearly unchanged. The results correlate well with the electrochemical behavior.

Place, publisher, year, edition, pages
2017. 10.1002/celc.201700395- p.
Keyword [en]
Li-ion batteries, LTO, binder, interface layer, photoelectron spectroscopy
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-331107DOI: 10.1002/celc.201700395OAI: oai:DiVA.org:uu-331107DiVA: diva2:1148390
Funder
Swedish Energy AgencyStandUp
Available from: 2017-10-10 Created: 2017-10-10 Last updated: 2017-10-13
In thesis
1. 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)
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Available from: 2017-11-10 Created: 2017-10-13 Last updated: 2017-11-10

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