Diffusion and Lattice Dynamics in Disordered Li Argyrodites

Lithium argyrodites Li6PS5X (X=Cl, Br) have been demonstrated as promising solid-state electrolytes (SSEs) for next-generation batteries owing to their high ionic conductivity. Yet, the key atomistic processes enabling their fast ionic diffusion remain poorly known. It is believed the X/S site disorder plays an important role in Li diffusion. However, this explanation ignores the correlated dynamics between Li diffusion and host lattice, which we have recently uncovered its importance. Specifically, based on inelastic neutron scattering and quasi-elastic neutron scattering measurements on Li6PS5Cl, supplemented with AIMD and machine-learning accelerated MD simulations, we have gained important insights into the coupling of fast ion diffusion with anharmonic framework phonons.

Here, we propose to study the lattice dynamics and ion diffusion on Li6PS5Br with different degrees of S/Br disorder by QENS (and INS). By this systematic study, we will separate effects of structural disorder vs framework vibrations on ionic conductivity, and also get a better understanding of the correlation between phonon dynamics and diffusion behavior in SSEs upon structural changes. This project will refine our understanding of the correlation between phonon dynamics and Li diffusion, building on top of our previous findings, and potentially provide an important insight into how to further increase ion diffusion in SSEs via phonon-engineering.