Untersuchung der Gelbildung und der Ionenmobilität nach Zugabe von oxidischen bzw. nitridischen Nanopartikeln zu Ionischer Flüssigkeit
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Philipps-Universität Marburg
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Abstract
For battery development, safety is a major issue. Therefore, many efforts were directed towards substitution of volatile and flammable solvents by viscous and thermally stable substances. With regard to security aspects, solids are the most promising electrolyte materials, but their disadvantage is generally lower ionic conductivity compared with liquids. To combine the positive properties of both material classes, there is a growing interest in quasi-solid electrolytes. One attempt is to solidify thermally and chemically stable ionic liquids (ILs) through addition of nanoparticles and to use the resulting ionogel as a new type of solvent for conducting salts.
The suitability of ionogels has already been proven in dye-sensitized solar cells and lithium ion-batteries. The main interest of current research is to understand the nature of the gelation process and, the resulting microstructure as well as its effect on the ionic conductivity. This systematic study presents the influence of the type of the dispersed particles on the colloidal interaction in ILs by comparing SiO2 and Si3N4 particles.
The viscoelastic behavior of the ionogels was investigated in order to better understand the interfacial effects. Dynamic shear experiments showed that 3 vol.-% nanoparticles of both types (either SiO2 or Si3N4) are sufficient to form a gel; however, the underlying gelation process of both systems is entirely different: The elastic modulus in dependence of the particle concentration demonstrates that the Si3N4 ionogels are formed through diffusion-controlled agglomeration and the SiO2 gels through reaction-controlled agglomeration. In contrast to the Si3N4 ionogel, the SiO2 ionogels show thixotropic behavior.
To obtain information about the interactions between particles, zeta-potential measurements were performed, for which monodisperse SiO2 particles were synthesized. The agglomeration behavior of SiO2 particles dispersed in ethanol was investigated in dependence of IL concentration. In addition to TEM-pictures, the results indicated that there is a distance of 10 nm between the SiO2 particles. This observation is attributed to solvation effects: To confirm this assumption, potential curves were calculated and compared qualitatively to experimental results of the rheological measurements.
The ion transport studies revealed that the overall conductivity of the ionogels decreased with increasing particle concentration. Qualitatively, this could be described by the effective medium theory (EMT). The deviation of the absolute values indicates that the forces between particles and the interactions between ions and surface are not negligible. NMR-experiments show that especially cations interact with the surface groups of the particle. A portion of the cations is trapped; these ions do not contribute to the conductivity of the sample. The amount of the immobilized ions in the Si3N4 ionogels is larger than in the SiO2 ionogels. Comparison of the self-diffusion coefficients shows that all ions apart from the lithium species are slowed down more strongly by the addition of Si3N4 particles than by adding SiO2.
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Created: 2013Issued: 2014-02-24Updated: 2014-02-24
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Fachbereich Chemie
Publisher
Philipps-Universität Marburg
Language
ger
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DoctoralThesis
Keywords
gelationionic liquidnanoparticleelectrolyte
DFG-subjects
GelierenIonische FlüssigkeitIonenleitungNanopartikelElektrolyt
DDC-Numbers
540
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Rößer, Carola: Untersuchung der Gelbildung und der Ionenmobilität nach Zugabe von oxidischen bzw. nitridischen Nanopartikeln zu Ionischer Flüssigkeit. : Philipps-Universität Marburg 2014-02-24. DOI: https://doi.org/10.17192/z2014.0085.
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This item has been published with the following license: In Copyright