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The influence of PMS-additive on the electrode/electrolyte interfaces in LiFePO4/graphite Li-ion batteries
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
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2013 (Engelska)Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 45, s. 23476-23486Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The influence of a film-forming additive, propargyl methanesulfonate (PMS), on electrochemical performance and electrode/electrolyte interface composition of LiFePO4/graphite Li-ion batteries has been studied. Combined use of in-house X-ray photoelectron spectroscopy (XPS) and soft and hard X-ray photoelectron spectroscopy (PES) enabled nondestructive depth profiling at four different probing depths in the 2-50 nm range. Cells cycled with PMS and LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC) were compared to a reference sample cycled without PMS. In the first cycle, PMS cells showed a higher irreversible capacity, which is explained by formation of a thicker solid electrolyte interphase (SEI). After three cycles, the SET thicknesses were determined to be 19 and 25 nm for the reference and PMS samples, respectively. After the initial cycling, irreversible losses shown by the PMS cells were lower than those of the reference cell. This could be attributed to a different SET composition and lower differences in the amount of lithium between lithiated and delithiated electrodes for the PMS sample. It was suggested that PMS forms a triple-bonded radical on reduction, which further reacts with the electrolyte. The PMS additive was shown to influence the chemical composition at the positive electrode/electrolyte interface. Thicker interface layers with higher C-O and smaller LiF contributions were formed on LiFePO4 cycled with PMS.

Ort, förlag, år, upplaga, sidor
2013. Vol. 117, nr 45, s. 23476-23486
Nationell ämneskategori
Materialkemi
Identifikatorer
URN: urn:nbn:se:uu:diva-197151DOI: 10.1021/jp4045385ISI: 000327110500005OAI: oai:DiVA.org:uu-197151DiVA, id: diva2:611749
Forskningsfinansiär
StandUpTillgänglig från: 2013-03-18 Skapad: 2013-03-18 Senast uppdaterad: 2017-12-30
Ingår i avhandling
1. Insights into Li-ion Battery and Stainless Steel Interfaces Using Refined Photoelectron Spectroscopy Methodology
Öppna denna publikation i ny flik eller fönster >>Insights into Li-ion Battery and Stainless Steel Interfaces Using Refined Photoelectron Spectroscopy Methodology
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2013. s. 69
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1031
Nationell ämneskategori
Materialkemi
Identifikatorer
urn:nbn:se:uu:diva-197153 (URN)978-91-554-8624-2 (ISBN)
Disputation
2013-05-03, Häggsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2013-04-12 Skapad: 2013-03-18 Senast uppdaterad: 2013-08-30Bibliografiskt granskad
2. The Complex Nature of the Electrode/Electrolyte Interfaces in Li-ion Batteries: Towards Understanding the Role of Electrolytes and Additives Using Photoelectron Spectroscopy
Öppna denna publikation i ny flik eller fönster >>The Complex Nature of the Electrode/Electrolyte Interfaces in Li-ion Batteries: Towards Understanding the Role of Electrolytes and Additives Using Photoelectron Spectroscopy
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2014. s. 74
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1129
Nyckelord
Li-ion battery, LiFePO4/graphite cell, interface, electrolyte additives, solid electrolyte interphase (SEI), photoelectron spectroscopy (PES), synchrotron
Nationell ämneskategori
Oorganisk kemi
Forskningsämne
Kemi med inriktning mot oorganisk kemi
Identifikatorer
urn:nbn:se:uu:diva-219336 (URN)978-91-554-8890-1 (ISBN)
Disputation
2014-04-11, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-03-20 Skapad: 2014-02-26 Senast uppdaterad: 2014-04-29

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