| 1. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Ab initio calculations, Raman and NMR investigation of the plastic crystal di-methyl pyrrolidinium iodide
- 2003
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Ingår i: Electrochimica Acta. - 0013-4686. ; 48:14-16, s. 2283-2289
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Tidskriftsartikel (refereegranskat)abstract
- Above 110 °C the symmetric di-methyl-pyrrolidinium iodide salt forms a plastic crystal phase of interest in the area of new electrolyte materials. In this study ab initio calculations of this material has been conducted in order to assign the vibrational spectra. Raman spectroscopy measurements on the solid salt as well as on the salt dissolved in different solvents has been performed and these have been compared to the theoretical spectra. Furthermore, Raman spectra as a function of temperature have been recorded to investigate possible changes in inter-ionic interaction and/or structure through the phase transition. 1 H NMR linewidth measurements as a function of temperature showed a large decrease in linewidth above 100 °C, attributed here to an increase in mobility in agreement with a previously reported phase transition at ∼ 110 °C. © 2003 Elsevier Science Ltd. All rights reserved.
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| 2. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Enhancement of ion dynamics in PMMA-based gels with addition of TiO2 nano-particles
- 2003
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Ingår i: Electrochimica Acta. - 0013-4686. ; 48:14-16, s. 2099-2103
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Tidskriftsartikel (refereegranskat)abstract
- Solvent and ion dynamics in PMMA based gels have been investigated as a function of the loading of nanosized TiO 2 particles. The gels have a molar ratio of 46.5:19:4.5:30 of ethylene carbonate (EC), propylene carbonate (PC), lithium perchlorate and PMMA, respectively. A series of samples with 0, 4, 6 and 8 wt.% TiO 2 filler were investigated. The diffusion coefficients for the lithium ions and for the two solvents (EC and PC) were investigated by pfg-NMR. It was shown that the addition of filler to the gel electrolytes enhances the diffusion of the cations, while the diffusion of the solvents remains constant. Raman measurements show no significant changes in ion-ion interactions with the addition of fillers, while the ionic conductivity is seen to decrease. However, the sample with 8 wt.% TiO 2 had a conductivity close to that of the unfilled sample. © 2003 Elsevier Science Ltd. All rights reserved.
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| 3. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Ion transport in polymer electrolytes containing nanoparticulate TiO2: The influence of polymer morphology
- 2003
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 5:4, s. 720-725
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that composite polymer electrolytes, formed by dispersing nanosized ceramic particles in polyether-based electrolytes, have improved ion transport properties as compared to their unfilled analogues. In the present study polymer electrolytes with different loadings of nano-sized ceramic particles (TiO 2 ) and different polymer chemistry and morphology have been investigated. Of special interest are filler induced effects on polymer, solvent and cationic mobility. Partly crystalline polymer electrolytes based on poly(ethylene oxide) have been compared to fully amorphous polymer electrolytes based on a polyether urethane, as well as gel electrolytes based on PMMA. 7 Li pfg-NMR, linewidth and spin-spin relaxation times as well as 1 H pfg-NMR and spin-spin relaxation times, were measured as a function of temperature and composition. The 1 H spin-spin relaxation measurements reveal increased average polymer mobility with the addition of filler up to a maximum at 4 and 8 wt.% TiO 2 for the fully amorphous and the partly crystalline electrolytes, respectively. The 7 Li linewidth measurements for the fully amorphous system show a broadening of the linewidth with addition of filler. Based on variable temperature measurements this broadening is interpreted as a result of the inhomogeneity introduced by the filler particles. Pulsed field gradient (pfg) diffusion measurements were employed to determine ion and solvent self-diffusion coefficients. In the case of the PMMA-based gel electrolyte and the fully amorphous electrolytes enhanced cation self-diffusion was observed upon addition of TiO 2 .
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| 4. |
- Adebahr, Josefina, 1973, et al.
(författare)
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Lithium coordination and mobility in gel electrolytes based on an acrylate polymer with ethylene oxide side chains
- 2003
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 13:4, s. 814-817
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Tidskriftsartikel (refereegranskat)abstract
- Multinuclear NMR has been used to investigate the structure and mobility of a series of polymer gel electrolytes. The co-polymers used as matrixes in the gels have acrylate backbones and side chains of ethylene oxide, where the length of the side chains has been varied, while the ratio of acrylate to ethylene oxide has been kept constant. The electrolyte is a mixture of lithium perchlorate and two solvents, ethylene carbonate and gamma butyrolactone. 13 C spectra of the different gel electrolytes shows that both solvents interact with the salt, and that the strength of the interaction increases with decreasing length of the polymer side chains. It also appears that the lithium ions show no selectivity between the two types of solvent. Furthermore, the lithium chemical shift moves progressively upfield with increasing length of the side chains, showing a gradual change in interaction from lithium-solvent to lithium-(ethylene oxide).
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| 5. |
- Adebahr, Josefina, 1973
(författare)
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Molecular Interactions and Dynamics in Lithium Conducting Electrolytes
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium conducting electrolytes, suitable for battery applications, have been characterized on a molecular level using Raman spectroscopy, ab initio calculations and nuclear magnetic resonance spectroscopy, in order to better understand molecular and ionic interactions and dynamics in the systems. Three different types of electrolytes have been investigated; polymer gel electrolytes, solid polymer electrolytes and plastic crystal materials, with the main focus on the polymer based electrolytes. Polymer gel electrolytes, comprised of a polymer swelled with a liquid electrolyte, are now replacing liquid electrolytes in lithium ion batteries. Extensive research efforts are still needed in order to optimize the performance of these materials. The molecular dynamics and ionic interactions in a series of gel electrolytes based on a co-polymer with an "inert" backbone, poly(methyl methacrylate), PMMA, and "active" side-chains, ethylene oxide, EO, are reported in this thesis. Furthermore, the effects of the addition of ceramic filler nano-particles to gel electrolytes based on PMMA, have been studied. An all solid-state-battery is a future goal, and solid polymer electrolytes show great potential. However, the ionic conductivity of these materials is still too low. Recently, the addition of nano-sized ceramic particles to solid polymer electrolytes has attracted considerable interest due to observed increases in conductivity, approaching values suitable for battery applications. The molecular interactions and dynamics have been investigated for different nanocomposite solid polymer electrolytes as a function of filler type and concentration. Other types of materials are also explored in the field of solid-state electrolytes. Plastic crystal materials have a number of advantageous properties, and it is possible to achieve high molecular/ionic diffusivities, as well as high conductivities. In this thesis the structure and vibrational properties of the different phases of an ionic plastic crystal material has been studied.
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