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MnSn2 electrodes for Li-ion batteries: Mechanisms at the nano scale and electrode/electrolyte interface
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - Ångström, Strukturkemi.
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2014 (Engelska)Ingår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 123, s. 72-83Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We have investigated the reaction mechanisms occurring upon the first discharge/charge cycle of a MnSn2//Li electrochemical cell, by using bulk- and surface-sensitive characterization techniques (Xray Diffraction, Sn-119 Mossbauer spectroscopy, magnetic measurements, X-ray photoelectron and Auger spectroscopies). Compared to other tin-transition metal alloys, MnSn2 displays an original behaviour. Lithium insertion into MnSn2 particles results in a nanocomposite consisting of Li7Sn2 phase, and of Mn nanoparticles which are immediately oxidized at their surface. Lithium extraction from this nanocomposite leads to the formation of magnetic MnSn2 particles and to our knowledge it is the first time such a mechanism is observed in tin-based intermetallic electrode materials due to electrochemical reaction with Li. The solid electrolyte interphase (SEI) is formed at the beginning of the first discharge and its thickness slightly increases upon further lithium insertion. A partial re-dissolution process occurs upon lithium extraction from the material, while its chemical composition is very stable over the whole cycle.

Ort, förlag, år, upplaga, sidor
elsevier, 2014. Vol. 123, s. 72-83
Nyckelord [en]
Lithium-ion batteries, MnSn2, Tin, Intermetallics, Mössbauer, XPS, Magnetism
Nationell ämneskategori
Materialkemi
Identifikatorer
URN: urn:nbn:se:uu:diva-198264DOI: 10.1016/j.electacta.2014.01.010ISI: 000334898800010OAI: oai:DiVA.org:uu-198264DiVA, id: diva2:615591
Tillgänglig från: 2013-04-11 Skapad: 2013-04-11 Senast uppdaterad: 2017-12-30
Ingår i avhandling
1. Insights in Li-ion Battery Interfaces through Photoelectron Spectroscopy Depth Profiling
Öppna denna publikation i ny flik eller fönster >>Insights in Li-ion Battery Interfaces through Photoelectron Spectroscopy Depth Profiling
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Compounds forming alloys with lithium, such as silicon or tin, are promising negative electrode materials for the next generation of Li-ion batteries due to their higher theoretical capacity compared to the current commercial electrode materials.

An important issue is to better understand the phenomena occurring at the electrode/electrolyte interfaces of these new materials. The stability of the passivation layer (SEI) is crucial for good battery performance and its nature, formation and evolution have to be investigated. It is important to follow upon cycling alloying/dealloying processes, the evolution of surface oxides with battery cycling and the change in surface chemistry when storing electrodes in the electrolyte.

The aim of this thesis is to improve the knowledge of these surface reactions through a non-destructive depth-resolved PES (Photoelectron spectroscopy) analysis of the surface of new negative electrodes. A unique combination utilizing hard and soft-ray photoelectron spectroscopy allows by variation of the photon energy an analysis from the extreme surface (soft X-ray) to the bulk (hard X-ray) of the particles. This experimental approach was used to access the interfacial phase transitions at the surface of silicon or tin particles as well as the composition and thickness/covering of the SEI.

Interfacial mechanisms occurring upon the first electrochemical cycle of Si-based electrodes cycled with the classical salt LiPF6 were investigated.

The mechanisms of Li insertion (LixSi formation) have been illustrated as well as the formation of a new irreversible compound, Li4SiO4, at the outermost surface of the particles. Upon long cycling, the formation of SiOxFy was shown at the extreme surface of the particles by reaction of SiO2 with HF contributing to battery capacity fading.

The LiFSI salt, more stable than LiPF6, improved the electrochemical performances. This behaviour is correlated to the absence of SiOxFy upon long-term cycling. Some degradation of LiFSI was shown by PES and supported by calculations.

Finally, interfacial reactions occurring upon the first cycle of an intermetallic compound MnSn2 were studied. Compared to Si based electrodes, the SEI chemical composition is similar but the alloying process and the role played by the surface metal oxide are different.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2013. s. 200
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1041
Nyckelord
Lithium-ion batteries, negative electrodes, silicon, MnSn2, SEI, PES, XPS, synchrotron
Nationell ämneskategori
Materialkemi Fysikalisk kemi
Forskningsämne
Kemi med inriktning mot oorganisk kemi
Identifikatorer
urn:nbn:se:uu:diva-197250 (URN)978-91-554-8662-4 (ISBN)
Disputation
2013-05-24, Amphithéâtre de l'IPREM, 2 avenue du Président Pierre Angot, Pau, France, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2013-05-03 Skapad: 2013-03-20 Senast uppdaterad: 2013-08-30Bibliografiskt granskad

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Förlagets fulltexthttp://dx.doi.org/10.1016/j.electacta.2014.01.010

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