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All silicon lithium-ion batteries
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. (Advanced Ångström Battery Center)
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Lithium-ion batteries have been widely used as power supplies for portable electronic devices due to their higher gravimetric and volumetric energy densities compared to other electrochemical energy storage technologies, such as lead-acid, Ni-Cd and Ni-MH batteries. Developing a novel battery chemistry, ‘‘all silicon lithium-ion batteries’’, using lithium iron silicate as the cathode and silicon as the anode, is the primary aim of this Ph.D project. This licentiate thesis is focused on improving the performance of the silicon anode via optimization of electrolyte composition and electrode formulation. Fluoroethylene carbonate (FEC) was investigated as an electrolyte additive for silicon composite electrodes, and both the capacity retention as well as coulombic efficiency were significantly improved by introducing 10 wt% FEC into the LP40 electrolyte. This is due to the formation of a stable SEI, which mainly consisted of FEC decomposition products of LiF, -CHFOCO2-, etc. The chemical composition of the SEI was identified by synchrotron radiation based photoelectron spectroscopy. This conformal SEI prevented formation of large amounts of cracks and continues electrolyte decomposition on the silicon electrode. An alternative lithium salt, lithium 4,5-dicyano-2-trifluoromethanoimidazole (LiTDI), was studied with the silicon electrode in this thesis. The SEI formation led to a rather low 1st cycle coulombic efficiency of 44.4%, and the SEI layer was found to contain hydrocarbon, ether-type and carbonate-type species. Different to conventional composite silicon electrodes, which require heavy and expensive copper current collector, a flexible silicon electrode, consisted of only silicon nanopowder, Cladophora nanocellulose and carbon nanotube, was facilely prepared via vacuum filtration. The electrode showed good mechanical, long-term cycling as well as rate capability performance.

Place, publisher, year, edition, pages
Uppsala universitet, 2015. , 47 p.
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-261626OAI: oai:DiVA.org:uu-261626DiVA: diva2:850809
Presentation
2015-09-24, 15:15 (English)
Opponent
Supervisors
Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2015-09-03Bibliographically approved
List of papers
1. Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive
Open this publication in new window or tab >>Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive
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2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 7, 2591-2599 p.Article in journal (Refereed) Published
Abstract [en]

Silicon as a negative electrode material for lithium-ion batteries has attracted tremendous attention due to its high theoretical capacity, and fluoroethylene carbonate (FEC) was used as an electrolyte additive, which significantly improved the cyclability of silicon-based electrodes in this study. The decomposition of the FEC additive was investigated by synchrotron-based X-ray photoelectron spectroscopy (PES) giving a chemical composition depth-profile. The reduction products of FEC were found to mainly consist of LiF and -CHF-OCO2-type compounds. Moreover, FEC influenced the lithium hexafluorophosphate (LiPF6) decomposition reaction and may have suppressed further salt degradation. The solid electrolyte interphase (SEI) formed from the decomposition of ethylene carbonate (EC) and diethyl carbonate (DEC), without the FEC additive present, covered surface voids and lead to an increase in polarization. However, in the presence of FEC, which degrades at a higher reduction potential than EC and DEC, instantaneously a conformal SEI was formed on the silicon electrode. This stable SEI layer sufficiently limited the emergence of large cracks and preserved the original surface morphology as well as suppressed the additional SEI formation from the other solvent. This study highlights the vital importance of how the chemical composition and morphology of the SEI influence battery performance.

National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:uu:diva-253257 (URN)10.1021/acs.chemmater.5b00339 (DOI)000353176100041 ()
Available from: 2015-05-26 Created: 2015-05-25 Last updated: 2017-12-04Bibliographically approved
2. A hard X-ray photoelectron spectroscopy study on the solid electrolyte interphase of a lithium 4,5-dicyano-2- (trifluoromethyl)imidazolide based electrolyte for Si-electrodes
Open this publication in new window or tab >>A hard X-ray photoelectron spectroscopy study on the solid electrolyte interphase of a lithium 4,5-dicyano-2- (trifluoromethyl)imidazolide based electrolyte for Si-electrodes
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2016 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 301, 105-112 p.Article in journal (Other academic) Published
Abstract [en]

This report focuses on the relatively new salt, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), and its functionality together with a silicon based composite electrode in a half-cell lithium ion battery context. LiTDI is a promising alternative to the commonly used LiPF6 salt because it does not form HF which can decompose the oxide layer on Si. The formation of a solid electrolyte interphase (SEI) as well as the development of the active Si-particles are investigated during the first electrochemical lithiation and de-lithiation. Characterizations are carried out at different state of charge with scanning electron microscopy (SEM) as well as hard x-ray photoelectron spectroscopy (HAXPES) at two different photon energies. This enables a depth resolved picture of the reaction processes and gives an idea of the chemical buildup of the SEI. The SEI is formed by solvent and LiTDI decomposition products and its composition is similar to SEI formed by other carbonate based electrolytes. The LiTDI salt or its decomposition products are not in itself reactive towards the active Si-material and no unwanted side reactions occurs with the active Si-particles. Despite some decomposition of the LiTDI salt, it is a promising alternative for electrolytes aimed towards Si-based electrodes.

Keyword
Lithium 4, 5-dicyano-2-(trifluoromethyl); imidazolide; Silicon negative electrode; Solid electrolyte interphase; Hard x-ray photoelectron spectroscopy
National Category
Natural Sciences Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-261159 (URN)10.1016/j.jpowsour.2015.09.112 (DOI)000365060500014 ()
Funder
VINNOVA, P37446-1EU, FP7, Seventh Framework ProgrammeEU, FP7, Seventh Framework ProgrammeEU, FP7, Seventh Framework Programme
Available from: 2015-08-31 Created: 2015-08-31 Last updated: 2017-12-04Bibliographically approved
3. Flexible freestanding Cladophora nanocellulose paper based Si anodes for lithium-ion batteries
Open this publication in new window or tab >>Flexible freestanding Cladophora nanocellulose paper based Si anodes for lithium-ion batteries
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2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 27, 14109-14115 p.Article in journal (Refereed) Published
Abstract [en]

Freestanding, lightweight and flexible Si paper anodes are prepared via a straightforward paper-making process using Cladophora nano-cellulose, silicon nanoparticles and carbon nanotubes as the building blocks. The uniform Si particle distribution and strong adhesion of the Si nanoparticles to the porous, conductive and flexible nanocellulose/carbon nanotube 3D matrix yield specific capacities of up to 800 mA h g(-1) (based on the weight of whole electrode) and very good cycling performances.

National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-259178 (URN)10.1039/c5ta02136g (DOI)000357257900006 ()
Funder
Swedish Foundation for Strategic Research , RMA-110012SweGRIDS - Swedish Centre for Smart Grids and Energy StorageCarl Tryggers foundation
Available from: 2015-07-29 Created: 2015-07-29 Last updated: 2017-12-04Bibliographically approved

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