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.