The discovery of superionic conductors has grown in popularity for its application as a solid-state electrolyte (SSE) in all-solid-state batteries (ASSBs). SSEs like Li10GeP2S12 and Li7P3S11 that exhibit superionic conductivity, or conductivity that exceeds its liquid phase, are postulated to be possible because of phonon-ion coupled conduction. Density Functional Theory, Molecular Dynamics (MD), and other computation techniques suggest that the rotation of polyanions, like PS43-, may assist in ion hopping via a paddle wheel mechanism. Although the paddle wheel mechanism relies heavily on the rotation of these polyanions, other phonon modes that involve polyhedral rocking motions are also theorized to affect ion migration. However, very few experimental studies can directly measure these many-body couplings of conduction-relevant phonon modes. In this work, we generate Terahertz (THz) fields to excite phonon modes up to 5.5 THz in a solid-state ion conductor Li0.5La0.5TiO3 (LLTO). The frequency range we excite includes phonon bands that have been predicted to drive ion hopping. The change in impedance is then monitored by electrochemical impedance spectroscopy. Driving the TiO6 rocking modes decreases the impedance by an order of magnitude compared to incoherently heating the entire phonon bath. We further support these observations with Nudged Elastic Band calculations and MD simulations. This proof-of-concept experiment lays the foundation for understanding phonon-ion coupled conduction in promising SSEs and design of superionic conductors for ASSBs.

Probing phonon coupled ion diffusion using THz excitation

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.