Servicenavigation

Project Details

Back

Projekt Print View

Ionic Charge Transport and Molecular Reorientation in Deep Eutectic Solvents studied by Dielectric Spectroscopy and Nuclear Magnetic Resonance

Subject Area Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Experimental Condensed Matter Physics
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 444797029
 
Final Report Year 2024

Final Report Abstract

Electrolytes, where ions carry the electrical current, are essential elements of devices such as batteries, fuel cells, or supercapacitors, needed for tomorrow's sustainable energy supply. To significantly improve them, finding electrolytes with enhanced properties is a key factor. Promising candidates are the deep eutectic solvents (DESs), multicomponent systems mostly consisting of a salt and a molecular material that can form hydrogen bonds (termed hydrogen bond donor). DESs are superior to common electrolytes, e.g., concerning environmental friendliness, reduced flammability, and costs. In these mixtures, a "zoo" of translational and rotational motions of the different particle types (charged symmetric and asymmetric ions and neutral molecules) exists. To develop DESs suitable for applications, a better understanding of the ion motions within this complex environment is prerequisite. To reach this aim, using a combination of experimental methods (dielectric spectroscopy, nuclear magnetic resonance, and rheology) we investigated various DESs and clarified how the different dynamics within them are coupled and how they impact on the technically relevant ionic conductivity. Moreover, we studied the glass transition in these materials and its effect on the conductivity. In all examined DESs, we found intricate relationships including different degrees of coupling among the different types of particle motion. Systematic investigations of related DESs revealed how the hydrogen bonding patterns influence these findings. NMR measurements enabled us to selectively examine the dynamics of the ion species or the hydrogen bond donor molecules. In DESs, a high mobility of small ions like lithium is required for technical applications. Using dielectric and mechanical spectroscopy, we investigated DESs containing either large or very small amounts of lithium salt. Generally, we found that the Li ions lead to stronger interparticle interactions, resulting in slower ionic dynamics. Therefore, also having in mind the relatively high cost and criticality of lithium, DESs with small amounts of lithium salt turned out preferable. For several DESs, we detected an enhanced lithium mobility compared to expectations for particles diffusing in a viscous medium, an effect promising for application. We also investigated ZnCl2-based DESs, proposed as electrolytes in zinc-ion batteries, and suggested how to optimize their room-temperature conductivity. As DESs often contain residual water, we also studied its influence on their properties, which are not dramatically varied even by moderate hydration. Moreover, we found that the lowtemperature glass formation of DESs can strongly affect their ionic conductivity, even at room temperature. Overall, our systematic studies on how the mentioned factors affect the conductivity of DESs and the resulting better understanding of the ionic motions help to pave the way for the development of new DES-based electrolytes.

Publications

 
 

Additional Information

© 2026 DFG Disclaimer / Copyright / Privacy Policy

Textvergrößerung und Kontrastanpassung