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Encasing Si particles within a versatile TiO2−xFx layer as an extremely reversible anode for high energy-density lithium-ion battery
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.ORCID iD: 0000-0001-5861-4281
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0002-8915-3032
Centre for Nano Energy Materials, State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China; Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, United States.
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2016 (English)In: Nano Energy, ISSN 2211-2855, Vol. 30, p. 745-755Article in journal (Refereed) Published
Abstract [en]

The chemical phenomena occurring at the electrode-electrolyte interfaces profoundly determine the cycle behavior of a lithium ion battery. In this work, we report that silicon-based anodes can attain enhanced levels of capacity retention, rate performance and lifespan when a versatile protective layer of, F-doped anatase (TiO2−xFx), is applied towards taming the interfacial chemistry of the silicon particles. With careful choice of titanium fluoride as a precursor, internal voids can be generated upon in-situ fluoride etching of the native oxide layer and are used to alleviate the mechanical stress caused by volume expansion of silicon during cycling. In the course of F-doping, part of the Ti4+(d0) ions in anatase are reduced to Ti3+(d1), thereby increasing charge carriers in the crystal structure. Hence, the multifunctional F-doped TiO2−x coating, not only minimizes the direct exposure of the Si surface to the electrolyte, but also improves the electronic conductivity via inter-valence electron hopping. The best-performing composite electrode, Si@TiO2−xFx-3, delivered a satisfactory performance in both half-cell and full-cell configurations. Furthermore, we present a study of 1) the Si valence change at the buried interface using synchrotron based hard X-ray photoelectron spectroscopy, and 2) the phase transformation of the electrode monitored in operando using X-ray diffraction. Based on these characterizations, we observe that the Li+ conducting intermediate phase (LixTiO2−xFx) formed inside the surface coating enables deep lithiation and delithiation of the silicon during battery operation, and thus increase the capacity that can be accessed from the electrodes.

Place, publisher, year, edition, pages
2016. Vol. 30, p. 745-755
Keyword [en]
Si anode, Versatile interfacial layer, Operando X-ray Diffraction, Kinetic activation, High energy-density
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-311358DOI: 10.1016/j.nanoen.2016.09.026ISI: 000390636100085OAI: oai:DiVA.org:uu-311358DiVA, id: diva2:1059845
Funder
Swedish Foundation for Strategic Research Swedish Research Council, 2012-4681StandUpSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Note

The second and third author contributed equally to this work

Available from: 2016-12-24 Created: 2016-12-24 Last updated: 2017-10-06Bibliographically approved
In thesis
1. Exploration of Non-Aqueous Metal-O2 Batteries via In Operando X-ray Diffraction
Open this publication in new window or tab >>Exploration of Non-Aqueous Metal-O2 Batteries via In Operando X-ray Diffraction
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Non-aqueous metal-air (Li-O2 and Na-O2) batteries have been emerging as one of the most promising high-energy storage systems to meet the requirements for demanding applications due to their high theoretical specific energy. In the present thesis work, advanced characterization techniques are demonstrated for the exploration of metal-O2 batteries. Prominently, the electrochemical reactions occurring within the Li-O2 and Na-O2 batteries upon cycling are studied by in operando powder X-ray diffraction (XRD).

In the first part, a new in operando cell with a combined form of coin cell and pouch cell is designed. In operando synchrotron radiation powder X-ray diffraction (SR-PXD) is applied to investigate the evolution of Li2O2 inside the Li-O2 cells with carbon and Ru-TiC cathodes. By quantitatively tracking the Li2O2 evolution, a two-step process during growth and oxidation is observed.

This newly developed analysis technique is further applied to the Na-O2 battery system. The formation of NaO2 and the influence of the electrolyte salt are followed quantitatively by in operando SR-PXD. The results indicate that the discharge capacity of Na-O2 cells containing a weak solvating ether solvent depends heavily on the choice of the conducting salt anion, which also has impact on the growth of NaO2 particles.

In addition, the stability of the discharge product in Na-O2 cells is studied. Using both ex situ and in operando XRD, the influence of sodium anode, solvent, salt and oxygen on the stability of NaO2 are quantitatively identified. These findings bring new insights into the understanding of conflicting observations of different discharge products in previous studies.

In the last part, a binder-free graphene based cathode concept is developed for Li-O2 cells. The formation of discharge products and their decomposition upon charge, as well as different morphologies of the discharge products on the electrode, are demonstrated. Moreover, considering the instability of carbon based cathode materials, a new type of titanium carbide on carbon cloth cathode is designed and fabricated. With a surface modification by loading Ru nanoparticles, the titanium carbide shows enhanced oxygen reduction/evolution activity and stability. Compared with the carbon based cathode materials, titanium carbide demonstrated a higher discharge and charge efficiency.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 71
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1572
Keyword
Keywords: lithium-oxygen batteries, sodium-oxygen batteries, metal-air, in operando X-ray diffraction, cathode materials
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-330889 (URN)978-91-513-0094-8 (ISBN)
Public defence
2017-11-24, ITC 1211, Lägerhyddsvägen 2, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-11-02 Created: 2017-10-06 Last updated: 2017-11-02

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