Inorganic Seminar
"Harnessing Static and Dynamic Disorder for Solid-state Ion Transport"
Abstract: Mastery over solid-state ion transport is paramount for broad diversity of applications and technologies, including batteries, fuel cells, neuromorphic computing, and beyond. Disorder – both static and dynamic – plays a crucial role in dictating ion diffusion in the solid state. Our work seeks to understand and harness disorder across time and length scales to impact ion transport processes. The argyrodites Li6PS5X (X = Cl–, Br–, I–, CN–) are amenable to a large degree of both static and dynamic disorder that conspire to influence mobile ion dynamics. Recently, we have identified signatures of PS4 rotational disorder in the local structure of the halide argyrodites Li6PS5X(X = Cl–, Br–, I–). The amplitude of these (presumably dynamic) rotations are correlated with the presence of site disorder and with higher lithium-ion conductivity. We further correlate the details of the local structure with the underlying contributions to lithium transport. To further explore the role of rotational dynamics in the argyrodite family, we have discovered the cyanide argyrodite Li6PS5(CN) in which the halide site is occupied by the orientationally-disordered cyanide ion. Through experimental and computational efforts, we find that the configuration of site disorder between the sulfide and cyanide anions leads to vast differences in the timescales of lithium ion hopping and cyanide rotational dynamics. The cyanide dynamics can be rationalized by considering how interactions between neighboring cyanides impact the energetic landscape for molecular rotations. We further explore the potential for coupled dynamics between lithium and cyanide. Taken together, our work highlights the complex interplay between static site disorder and the dynamics of molecular/polyhedral species and their impact on ion transport in argyrodite solid-state ion conductors.