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Regensburg 2022 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 13: Charged Soft Matter, Polyelectrolytes and Ionic Liquid

CPP 13.5: Talk

Tuesday, September 6, 2022, 10:45–11:00, H38

Tuning water-in-salt electrolytes: impact of concentration and anion structure on local and long-ranged dynamics probed by NMR — •Dominik Gappa, Elisa Steinrücken, Manuel Becher, and Michael Vogel — TU Darmstadt, Institut für Physik kondensierter Materie, Darmstadt, Germany

Water-in-salt electrolytes (WiSE) are highly concentrated aqueous solutions of (Li-)salts. Newly developed WiSE, as they are nonflammable, nontoxic, have a high lithium-ion density and a wide electrochemical stability window (ESW), are promising materials for applications as lithium-ion electrolytes. Due the high amount of the solute and, thus, strong electrostatic interactions between the components they show complex molecular dynamics. A full understanding of interaction mechanism, e.g. the impact of the concentration and anion structure on the dynamics is still elusive. We investigate LiTFSI, which has a wide ESW for different salt concentrations in water. In particular, we exploit the isotope selectivity of Nuclear Magnetic Resonance (NMR) to observe the behavior of the constituents of LiTFSI-H2O mixtures with various concentrations separately via 1H, 7Li and 19F NMR. The anion structure is modified by extending one side group of the originally symmetric TFSI anion, leading to increasingly heterogeneous dynamics. Local dynamics are investigated by spin-lattice relaxation, including field-cycling NMR, and long-ranged transport by diffusion experiments. Rotational correlation times and diffusion coefficients are extracted to scruntinize the validity of the Stokes-Einstein relation.

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