| 1. |
- Fu, Yifeng, 1984, et al.
(author)
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Selective growth of double-walled carbon nanotubes on gold films
- 2012
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In: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 72, s. 78-80
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Journal article (peer-reviewed)abstract
- Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the as-grown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended.
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| 2. |
- Kim, Jae-Kwang, 1978, et al.
(author)
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Electrochemical properties of a full cell of lithium iron phosphate cathode using thin amorphous silicon anode
- 2014
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In: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 268:Part B, s. 256-260
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Journal article (peer-reviewed)abstract
- Carbon-coated lithium iron phosphate (LiFePO4/C) with uniform carbon coating was synthesized by a mechanical activation method. Silicon negative electrode material was obtained in the form of thin films of amorphous silicon on a Cu foil substrate by vertical deposition technique. The electrochemical performance of the full cell, LiFePO4/C-Si, was tested with 1 M LiPF6 in EC/DMC at 0.5 and 1 C-rates. The cell exhibited an initial discharge capacity of 143.9 mAh g(-1) at 0.5 C-rate at room temperature. A reasonably good cycling performance under a high current density of 1 C-rate could be obtained with the full cell.
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| 3. |
- Martinelli, Anna, 1978, et al.
(author)
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Conformational evolution of TFSI− in protic and aprotic ionic liquids
- 2011
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In: Journal of Raman Spectroscopy. - 0377-0486 .- 1097-4555.
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Journal article (peer-reviewed)abstract
- We here report on the conformational evolution of the bis(trifluoromethanesulfonyl)imide anion (TFSI−) in protic and aprotic TFSI−-based ionic liquids as a function of temperature. The investigation is performed by Raman spectroscopy in the spectral ranges 240-380 cm−1 and 715-765 cm−1, where the interference from bands due to the cations is negligible. The contribution from each TFSI− conformation, i.e. the cisoid (C1) and the transoid (C2), is quantified in order to estimate the enthalpy of conformational change, ΔH, which is found to be in the range 3.4–7.3 kJ/mol in the liquid state. Conformational information is for the first time determined from the 740 cm−1 band, which previously mainly has been used as an indicator of ion-ion interactions. The similarity in ΔH values obtained from the two spectral ranges demonstrates the validity of using also the 740 cm−1 band for the quantification of the TFSI conformational evolution.
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| 4. |
- Nordström, Jonas, 1980, et al.
(author)
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Aggregation, ageing and transport properties of surface modified fumed silica dispersions
- 2010
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 6:10, s. 2293-2299
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Journal article (peer-reviewed)abstract
- We have investigated the aggregation, ageing and transport properties of surface modified silica dispersions in DMSO by photon correlation spectroscopy and conductivity measurements. The surface modification introduces Li+-ions that dissociate in the dispersion creating a single Li+-ion conducting electrolyte. We show that the surface modification changes the aggregation and ageing properties of the material. There is a pronounced ageing observed for the modified silica dispersions. At high concentrations of fumed silica a gel state is found, which in the case of the surface modified silica is a very weak gel that can be rejuvenated by ultrasonic treatment. The key parameter controlling the aggregation in this system is hydrogen bonding and the surface modification results in a very low number of sites for hydrogen bonding. In addition there is a contribution from repulsive electrostatic interactions in the surface modified silica dispersions due to the highly charged surfaces of these particles. Furthermore, the Li+-ion diffusion, at low silica concentration, is three orders of magnitude faster than that of the silica particles and in the gel state the silica particles are immobile. We also find that the Li+-ion diffusion is virtually independent of the silica concentration in the dispersions.
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| 5. |
- Pitawala, Jagath, 1976, et al.
(author)
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Phase behaviour, transport properties, and interactions in Li-salt doped ionic liquids
- 2012
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In: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 154, s. 71-80
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Journal article (peer-reviewed)abstract
- We report on the influence of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) doping on the glass transition temperature (T(g)), the ionic conductivity, and Li-ion coordination of two dicationic ionic liquids (DILs) based on the TFSI anion. The results are compared to the behaviour of traditional mono-cationic ionic liquids. The cations of the DILs contain two imidazolium rings, connected by a decane hydrocarbon chain. Homogeneous mixtures of these ILs and LiTFSI can be obtained in a large concentration range. With increasing Li-salt concentration the ionic conductivity decreases whereas the glass transition temperature increases in both systems. However, the influence of the salt doping on the ionic conductivity and the glass transition temperature is low compared to typical mono-cationic ionic liquids, based on for example the pyrrolidinium cation and the TFSI anion. This behaviour is mirrored in the average coordination number of TFSI anions around Li-ions, determined by Raman spectroscopy. The coordination number is systematically lower in the DILs, suggesting a connection between the difference in the Li-ion environment and the behaviour of the glass transition and the ionic conductivity. A T(g)-scaled Arrhenius plot of the ionic conductivity shows that the ionic conductivity for all LiTFSI concentrations has the same temperature dependence, i.e. the fragility of the liquid is the same. This implies that the conduction process is dominated by the viscous properties of the liquids over the entire concentration range. This provides further support for linking the local environment of the Li-ions to the glass transition and conduction process in the ionic liquid/salt mixtures.
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| 6. |
- Xiong, Shizhao, et al.
(author)
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Analysis of the solid electrolyte interphase formed with an ionic liquid electrolyte for lithium-sulfur batteries
- 2014
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 252, s. 150-155
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Journal article (peer-reviewed)abstract
- We have investigated the formation of the solid electrolyte interphase (SEI) on lithium electrodes in the presence of an ionic liquid electrolyte with a particular focus on the influence of polysulfides present in the electrolyte on the SEI. The electrochemical performance of symmetric cells with lithium electrodes and electrolytes composed of N-Methyl-(n-butyl)pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) and LiTFSI, with and without the addition of polysulfides, were analyzed as well as the chemical composition of the SEI, before and after cycling. The cycling behavior of the symmetrical cells shows that the SEI films are relatively stable in the ionic liquid electrolyte, also in the presence of polysulfides. However, the presence of polysulfides results in a higher SEI layer resistance (R-SEI) and a higher activation energy. From X-ray photoelectron spectroscopy spectra (XPS), with argon-ion sputtering for depth profiling, we find that the SEI is formed by decomposition products from both cations and anions of the electrolyte. The XPS spectra show that the presence of polysulfides alters the decomposition process of the electrolyte, resulting in a SEI film with different chemical composition and structure, in line with the results from the electrochemical performance.
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| 7. |
- Åkesson, Dan, 1970, et al.
(author)
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Synthesis and Characterization of a cross-linkable polylactic acid based resin
- 2010
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In: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 115:1, s. 480-486
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Journal article (peer-reviewed)abstract
- A new biobased polyester resin was developed for thermoset composite applications. The resin is potentially inexpensive and can be produced industrially by relatively simple means. The resin consists of star-shaped methacrylated oligomers of lactic acid (LA). LA oligomers were synthesized in a two-step process: in the first step, oligomers of LA were polymerized by direct condensation of LA. In the second step, the oligomers were end-functionalized by methacrylic anhydride. The resin was characterized by differential scanning calorimetry, Raman spectroscopy, NMR, rubber process analyzer, and TOF-SIMS. Tests show that the resin can be crosslinked into a rigid network within a couple of minutes upon thermal initiation.
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| 8. |
- Kim, Jae-Kwang, 1978, et al.
(author)
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An Imidazolium based ionic liquid electrolyte for lithium batteries
- 2010
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 195:22, s. 7639-7643
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Journal article (peer-reviewed)abstract
- An electrolyte for lithium batteries based on the ionic liquid 3-methy-1-propylimidazolium bis(trifluoromethysulfony)imide (PMIMTFSI) complexed with lithium bis(trifluoromethysulfony)imide (LiTFSI) at a molar ratio of 1:1 has been investigated. The electrolyte shows a high ionic conductivity (1.2 × 10−3 S cm−1) at room temperature. Over the whole investigated temperature range the ionic conductivity is more than one order of magnitude higher than for an analogue electrolyte based on N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) complexed with LiTFSI and used here as a benchmark. Raman results indicate furthermore that the degree of lithium coordinated TFSI is slightly lower in the electrolyte based on PMIMTFSI and thus that the Li+ charge carriers should be higher than in electrolytes based on Py14TFSI. An ionic liquid gel electrolyte membrane was obtained by soaking a fibrous fully interconnected membrane, made of electrospun P(VdF-HFP), in the electrolyte. The gel electrolyte was cycled in Li/ionic liquid polymer electrolyte/Li cells over 15 days and in Li/LiFePO4 cells demonstrating good interfacial stability and highly stable discharge capacities with a retention of >96% after 50 cycles (146 mAh g−1).
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| 9. |
- Lombardo, L., et al.
(author)
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In-situ gelled electrolyte for lithium battery: Electrochemical and Raman characterization
- 2014
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 245, s. 232-235
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Journal article (peer-reviewed)abstract
- n this paper we report a polymer lithium cell using a PVdF-based, gel-type electrolyte formed in-situ during cell assembly. The gel electrolyte formation is monitored prior to cell assembly by electro-chemical impedance spectroscopy and by Raman spectroscopy in order to determine the characteristics of the lithium salt diffusion into the gel-membrane. The results show an efficient gel formation and a fast lithium salt diffusion, this finally resulting in an optimized behaviour in a lithium cell using a high voltage spinel-type cathode. We believe that the results here reported may contribute to the enhancement of the safety of lithium batteries. (C) 2013 Elsevier B.V. All rights reserved.
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