ABSTRACT
“Water-in-salt” electrolytes have recently been developed for Li-ion batteries, combining the safety and environmental friendliness of aqueous electrolytes with a larger operating window made possible by a solid-electrolyte interphase. Structural relaxation of the water dynamics and ionic framework in the ns time domain has been studied with QENS on H2O and D2O solutions of LiTFSI at 13.9m and 21m concentrations [1]. The data were Fourier transformed to obtain intermediate scattering functions (ISFs) and compared with corresponding quantities obtained from MD simulations. Comparison of the results from H2O and D2O solutions reveals much faster water dynamics compared with structural relaxation of the ionic framework, consistent with the nano-domain picture where the lithium diffusion occurs through the tortuous water domain around the slower relaxing ionic matrix. The structural relaxation has been correlated with the shear relaxation measured by transverse ultrasound [2] which shows a strong frequency dependence in the MHz time domain characteristic of non-Newtonian fluids. We have also measured the sound velocity and longitudinal viscosity with Brillouin scattering at a frequency of 2.3 GHz. The frequency dependence of the longitudinal viscosity [3] has also been measured in the MHz regime and shows a strong relaxation. By combining the shear and longitudinal viscosities the bulk viscosity can be determined. The ratio of bulk to shear viscosity is found to be almost independent of frequency but strongly dependent on LiTFSI concentration.
References:
(1) M. A. González et al., J. Phys. Chem. Lett. 11, 7279 (2020); (2) T. Yamaguchi & T. Matsuoka, Jpn. J. Appl. Phys. 61, SG1021 (2022); (3) A. S. Dukhin & P. J. Goetz, J. Chem. Phys. 130, 124519 (2009).
BIOGRAPHY
Prof. David Price obtained a Ph.D. in physics from the University of Cambridge. He was senior scientist, director of the Solid-State Science Division, and director of the Intense Pulsed Neutron Source at Argonne National Laboratory, and executive director of the High-Flux Isotope Reactor and Center for Neutron Scattering, Oak Ridge National Laboratory. He is currently a research scientist at the CEMHTI, Orléans, France. His research interests include order and disorder in solids and liquids, dynamics of disordered systems, glass transition and melting, neutron and synchrotron X-ray scattering, and materials for energy conversion and storage. He is fellow of the American Physical Society, Fellow of the Institute of Physics, and Fellow of the Neutron Scattering Society of America. He was a Distinguished Visiting Professor, Graduate University for Advanced Studies, Hayama, Japan and received the Alexander Von Humboldt Research Award and the American Crystallographic Association’s Warren Prize.
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