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Comparing anode and cathode electrode/electrolyte interface composition and morphology using soft and hard X-ray photoelectron spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
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2013 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 97, 23-32 p.Article in journal (Refereed) Published
Abstract [en]

Electrode/electrolyte interface depth profiling was performed on lithiated graphite and delithiated lithium iron phosphate electrodes after electrochemical cycling in a balanced full cell configuration containing a carbonate based LiPF6 electrolyte. The profiling was performed by synchrotron radiation based hard X‑ray photoelectron spectroscopy, HAXPES, and soft X‑ray photoelectron spectroscopy, SOXPES. In this way, the probing depth was varied over a wide range in the order of 2-50 nm. Both more surface and more bulk sensitive investigations than possible using traditional in-house X‑ray photoelectron spectroscopy (XPS) could thus be performed. The composition and morphology of the lithiated graphite anode/electrolyte interface (solid electrolyte interphase, SEI) and the delithiated lithium iron phosphate cathode/electrolyte interface (solid permeable interface, SPI) were compared. In the vicinity of the highly reductive graphite active material in the SEI, low binding energy components like Li2O were found while no obvious composition gradients were observed in the SPI. Both in the cathode SPI and the anode SEI, significant amounts of C-O and P‑F containing compounds were found to deposit during cycling. Evidence for mixing of the porous binder and other SEI/SPI components was observed in both the anode and cathode electrode/electrolyte interfaces. The lithiated graphite SEI was estimated to be of the order of two tens of nanometers, while the cathode SPI thickness was estimated to a few nanometers only. 

Place, publisher, year, edition, pages
2013. Vol. 97, 23-32 p.
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-196469DOI: 10.1016/j.electacta.2013.03.010ISI: 000319024500004OAI: oai:DiVA.org:uu-196469DiVA: diva2:610200
Available from: 2013-03-08 Created: 2013-03-08 Last updated: 2017-12-06
In thesis
1. Insights into Li-ion Battery and Stainless Steel Interfaces Using Refined Photoelectron Spectroscopy Methodology
Open this publication in new window or tab >>Insights into Li-ion Battery and Stainless Steel Interfaces Using Refined Photoelectron Spectroscopy Methodology
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

If sacrificing some of its material to form a passivating layer at the surface, materials may expand the range of environments where they can be used and further material degradation can decrease. This thesis aims to contribute with insights into passivating layers on especially Li-ion battery anodes (solid electrolyte interphase, SEI) but also on stainless steels, as well as the non-passivating Li-ion battery cathode/electrolyte interface layers (solid permeable interface, SPI). The studies have been performed using new possibilities offered by photoelectron spectroscopy techniques.

Depth gradients in the SEI and SPI layers were studied by combining synchrotron-based hard and soft X-ray photoelectron spectroscopy (HAXPES and SOXPES), which was further developed for Li-ion battery investigations. Stainless steel depth profiles were acquired combining HAXPES with angle resolved X-ray photoelectron spectroscopy (ARXPS).

In the Li-ion battery, organic species were more common in the outermost SEI, while some inorganic compounds were only detected in the more bulk sensitive measurements. No depth gradients were observed in the SPI. The interface between the graphite and the SEI was studied for the first time indicating lithium enrichment at the graphite surface. Furthermore, the influence of the film-forming additive propargyl methanesulphonate (PMS) on the electrode/electrolyte interfaces was studies, and cells cycled to end of life at 22°C and 55°C were compared.

For stainless steels, the thicknesses of the oxide film as well as the nickel enriched metal layer underneath the oxide were determined. A similar methodology was applied to estimate the Li-ion battery SEI thickness.

Finally, experiences from PES methodology work on the Li-ion battery systems are discussed aiming to facilitate further studies of the experimentally challenging electrochemically modified samples.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 69 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1031
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-197153 (URN)978-91-554-8624-2 (ISBN)
Public defence
2013-05-03, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-04-12 Created: 2013-03-18 Last updated: 2013-08-30Bibliographically approved
2. The Complex Nature of the Electrode/Electrolyte Interfaces in Li-ion Batteries: Towards Understanding the Role of Electrolytes and Additives Using Photoelectron Spectroscopy
Open this publication in new window or tab >>The Complex Nature of the Electrode/Electrolyte Interfaces in Li-ion Batteries: Towards Understanding the Role of Electrolytes and Additives Using Photoelectron Spectroscopy
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The stability of electrode/electrolyte interfaces in Li-ion batteries is crucial to the performance, lifetime and safety of the entire battery system. In this work, interface processes have been studied in LiFePO4/graphite Li-ion battery cells. 

The first part has focused on improving photoelectron spectroscopy (PES) methodology for making post-mortem battery analyses. Exposure of cycled electrodes to air was shown to influence the surface chemistry of the graphite. A combination of synchrotron and in-house PES has facilitated non-destructive interface depth profiling from the outermost surfaces into the electrode bulk. A better understanding of the chemistry taking place at the anode and cathode interfaces has been achieved. The solid electrolyte interphase (SEI) on a graphite anode was found to be thicker and more inhomogeneous than films formed on cathodes. Dynamic changes in the SEI on cycling and accumulation of lithium close to the carbon surface have been observed.   

Two electrolyte additives have also been studied: a film-forming additive propargyl methanesulfonate (PMS) and a flame retardant triphenyl phosphate (TPP). A detailed study was made at ambient and elevated temperature (21 and 60 °C) of interface aging for anodes and cathodes cycled with and without the PMS additive. PMS improved cell capacity retention at both temperatures. Higher SEI stability, relatively constant thickness and lower loss of cyclable lithium are suggested as the main reasons for better cell performance. PMS was also shown to influence the chemical composition on the cathode surface.

The TPP flame retardant was shown to be unsuitable for high power applications. Low TPP concentrations had only a minor impact on electrolyte flammability, while larger amounts led to a significant increase in cell polarization. TPP was also shown to influence the interface chemistry at both electrodes.

Although the additives studied here may not be the final solution for improved lifetime and safety of commercial batteries, increased understanding has been achieved of the degradation mechanisms in Li-ion cells. A better understanding of interface processes is of vital importance for the future development of safer and more reliable Li-ion batteries.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1129
Keyword
Li-ion battery, LiFePO4/graphite cell, interface, electrolyte additives, solid electrolyte interphase (SEI), photoelectron spectroscopy (PES), synchrotron
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-219336 (URN)978-91-554-8890-1 (ISBN)
Public defence
2014-04-11, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-20 Created: 2014-02-26 Last updated: 2014-04-29

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Malmgren, SaraCiosek, KatarzynaHahlin, MariaGustafsson, TorbjörnRensmo, HåkanEdström, Kristina

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