Laser-driven impedance spectroscopy measures the enabling role of ultrafast chemical and vibrational correlations during ion hopping in solid-state electrolytes Scott Cushing California Institute of Technology, USA The chemical and molecular interactions within a battery is a growing area of interest for physical chemistry. The electrolyte and electrode, as well as their interface, are a complex framework of ionic and electronic interactions happening on a vast variety of timescales. For example, ion hopping times can reach the picosecond timescales in solid-state superionic conductors through a complex interplay of ion-phonon, ion-electron, and ion-ion correlations. In this presentation, we present a new laser-derived technique that can directly measure ultrafast ion hopping on its inherent timescale. As a result, the relative contributions of the different correlations to the many-body, but chemistry dominated, ion hopping Hamiltonian are determined. The technique sweeps a broad-frequency range laser across the UV to THz to perturb AC impedance measurements in the grain boundary and bulk ion hopping regimes. High GHz conduction traces measure the picoseconds change in the ion hopping following the perturbation. With proper renormalization, the changes give the relative ion-electron and ion-phonon coupling terms. We demonstrate the technique on Li 0.5 La 0.5 TiO 3 (LLTO). For this solid-state material, we measure that the dominant ion hopping route is through a near-singular THz rocking mode (matching theoretical predictions). The relative role of ion-electron correlations relative to the ion-phonon correlations is also measured. Finally, we discuss how in the future the technique can be extended to measure ion-ion correlations. The technique is equally applicable to both solid-state and polymer-like materials as well as the electrode and electrode-electrolyte interface.
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© The Author(s), 2023
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