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Computational Studies of Nanotube Growth, Nanoclusters and Cathode Materials for Batteries
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Density functional theory has been used to investigate cathode materials for rechargeable batteries, carbon nanotube interactions with catalyst particles and transition metal catalyzed hydrogen release in magnesium hydride nanoclusters.

An effort has been made to the understand structural and electrochemical properties of lithium iron silicate (Li2FeSiO4) and its manganese-doped analogue. Starting from the X-ray measurements, the crystal structure of Li2FeSiO4 was refined, and several metastable phases of partially delithiated Li2FeSiO4 were identified. There are signs that manganese doping leads to structural instability and that lithium extraction beyond 50% capacity only occurs at impractically high potentials in the new material.

The chemical interaction energies of single-walled carbon nanotubes and nanoclusters were calculated. It is found that the interaction needs to be strong enough to compete with the energy gained by detaching the nanotubes and forming closed ends with carbon caps. This represents a new criterion for determining catalyst metal suitability. The stability of isolated carbon nanotube fragments were also studied, and it is argued that chirality selection during growth is best achieved by exploiting the much wider energy span of open-ended carbon nanotube fragments.

Magnesium hydride nanoclusters were doped with transition metals Ti, V, Fe, and Ni. The resulting changes in hydrogen desorption energies from the surface were calculated, and the associated changes in the cluster structures reveal that the transition metals not only lower the desorption energy of hydrogen, but also seem to work as proposed in the gateway hypothesis of transition metal catalysis.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2009. , p. 59
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 670
Keywords [en]
Materials science, density functional theory, cathode materials, hydrogen-storage materials, carbon nanotube growth
National Category
Other Physics Topics
Research subject
Physics of Matter; Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-108261ISBN: 978-91-554-7603-8 (print)OAI: oai:DiVA.org:uu-108261DiVA, id: diva2:234815
Public defence
2009-10-23, Polhemsalen, Ångströmlaboratoriet, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-10-01 Created: 2009-09-10 Last updated: 2009-10-01
List of papers
1. An ab initio study of the Li-ion battery cathode material Li2FeSiO4
Open this publication in new window or tab >>An ab initio study of the Li-ion battery cathode material Li2FeSiO4
2006 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 8, no 5, p. 797-800Article in journal (Refereed) Published
Abstract [en]

A density functional theory (DFT) calculation is reported for the novel Li-ion battery cathode material lithium iron silicate (Li2FeSiO4) and for three possible Li arrangements in the delithiated structure (LiFeSiO4). Relevant battery-related properties have been derived: average voltage (2.77 V vs. Li/Li+), energy density (1200 Wh/l) and specific energy (440 Wh/kg). Lattice constants and atomic fractional coordinates are also given for each case. The calculated values are in good agreement with recent experimental values (A. Nytén, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun., 7 (2005) 156). Voltages were calculated (again vs. Li/Li+) for the three different Li arrangements in LiFeSiO4; these differed by 0.22 V – a difference which could perhaps be related to the experimentally observed 0.30 V drop in voltage between the first and subsequent charge cycles.

Keywords
Li2FeSiO4, Lithium iron silicate, Cathode material, Li-ion battery, Density functional theory
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-94467 (URN)10.1016/j.elecom.2006.03.012 (DOI)
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2017-12-14Bibliographically approved
2. Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
Open this publication in new window or tab >>Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 4, p. 043510-Article in journal (Refereed) Published
Abstract [en]

In this paper, we report on Na2FePO4F and Li2FePO4F, which are materials that are used as cathodes in batteries, using density functional theory with the LDA, LDA + U, GGA, or GGA + U approximations. Specifically, we study their crystal structure, electronic structure, and magnetic properties and provide similar information about the intermediate compounds LiFePO4F and NaFePO4F. Finally, the intercalation voltages of the corresponding batteries are calculated using various exchange-correlation approximations and conclusions are drawn about which one is the most suitable to use for the study of this class of materials.

Place, publisher, year, edition, pages
American Institute of Physics, 2009
National Category
Physical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-108262 (URN)10.1063/1.3202384 (DOI)000270083800025 ()
Available from: 2009-09-10 Created: 2009-09-10 Last updated: 2017-12-13Bibliographically approved
3. Calculating carbon nanotube–catalyst adhesion strengths
Open this publication in new window or tab >>Calculating carbon nanotube–catalyst adhesion strengths
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2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 11, p. 115419-Article in journal (Refereed) Published
Abstract [en]

Density-functional theory is used to assess the validity of modeling metal clusters as single atoms or rings of atoms when determining adhesion strengths between clusters and single-walled carbon nanotubes (SWNTs). Representing a cluster by a single atom or ring gives the correct trends in SWNT-cluster adhesion strengths (Fe ≈ Co > Ni), but the single-atom model yields incorrect minimum-energy structures for all three metals. We have found that this is because of directional bonding between the SWNT end and the metal cluster, which is captured in the ring model but not by the single atom. Hence, pairwise potential models that do not describe directional bonding correctly, and which are commonly used to study these systems, are expected to give incorrect minimum-energy structures.

National Category
Physical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-108263 (URN)10.1103/PhysRevB.75.115419 (DOI)000245329600124 ()
Available from: 2009-09-10 Created: 2009-09-10 Last updated: 2017-12-13Bibliographically approved
4. The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes
Open this publication in new window or tab >>The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes
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2008 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 2, p. 463-468Article in journal (Refereed) Published
Abstract [en]

Density functional theory is used to show that the adhesion between single-walled carbon nanotubes (SWNTs) and the catalyst particles from which they grow needs to be strong to support nanotube growth. It is found that Fe, Co, and Ni, commonly used to catalyze SWNT growth, have larger adhesion strengths to SWNTs than Cu, Pd, and Au and are therefore likely to be more efficient for supporting growth. The calculations also show that to maintain an open end of the SWNT it is necessary that the SWNT adhesion strength to the metal particle is comparable to the cap formation energy of the SWNT end. This implies that the difference between continued and discontinued SWNT growth to a large extent depends on the carbon-metal binding strength, which we demonstrate by molecular dynamics (MD) simulations. The results highlight that first principles computations are vital for the understanding of the binding strength's role in the SWNT growth mechanism and are needed to get accurate force field parameters for MD.

National Category
Other Physics Topics
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-108264 (URN)10.1021/nl072431m (DOI)000253166200016 ()18162001 (PubMedID)
Available from: 2009-09-10 Created: 2009-09-10 Last updated: 2017-12-13Bibliographically approved
5. Copper/Molybdenum Nanocomposite Particles as Catalysts for the Growth of Bamboo-Structured Carbon Nanotubes
Open this publication in new window or tab >>Copper/Molybdenum Nanocomposite Particles as Catalysts for the Growth of Bamboo-Structured Carbon Nanotubes
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2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 32, p. 12201-12206Article in journal (Refereed) Published
Abstract [en]

Bamboo-structured carbon nanotubes (BCNTs), with mean diameters of 20 nm, have been synthesized on MgO-supported Cu and Mo catalysts by the catalytic chemical vapor deposition of methane. BCNTs could only be generated using a combination of Cu and Mo catalysts. No BCNTs were produced from either individual Cu or Mo catalysts. In combination, Mo was found to be essential for cracking the methane precursor, while Cu was required for BCNT formation. Energy dispersive X-ray analysis of the individual particles at the tips of the nanotubes suggest that Cu and Mo are present as a “composite” nanoparticle catalyst after growth. First-principles modeling has been used to describe the interaction of the Cu/Mo catalyst with the nanotubes, suggesting that the catalyst binds with the same energy as traditional catalysts such as Fe, Ni, and Co.

National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-108265 (URN)10.1021/jp8023556 (DOI)000258290100026 ()
Available from: 2009-09-10 Created: 2009-09-10 Last updated: 2017-12-13Bibliographically approved
6. Role of Catalyst in Dehydrogenation of MgH2 Nanoclusters
Open this publication in new window or tab >>Role of Catalyst in Dehydrogenation of MgH2 Nanoclusters
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2008 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 24, p. 8227-8231Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-96881 (URN)10.1073/pnas.0711743105 (DOI)
Available from: 2008-03-20 Created: 2008-03-20 Last updated: 2017-12-14Bibliographically approved

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