(Battery Division Student Research Award Sponsored by Mercedes-Benz Research & Development) Rationalizing Fast Lithium-ion Diffusion in Inorganic Lithium Superionic Conductors

All-solid-state batteries are gaining attention due to the potential advantage that solid electrolytes provide in terms of safety and energy density. Understanding the mechanism of fast lithium-ion diffusion in inorganic materials has become one of the key challenges in materials science. Among various factors that affect lithium mobility, the topology of the crystal structure strongly dictates which materials can accommodate fast lithium-ion motion. Despite this, the intrinsic mechanism that connects the lithium-ion diffusion to the structural feature of the crystal structure and motion of the non-diffusing framework remains unclear, hindering the rational design of novel fast-conducting solid electrolytes. This talk focuses on the fundamental understanding of the structure-property relationship of lithium-ionic conductivities. We first discuss the structural factors governing fast lithium-ion diffusion in oxide materials. We find that both the topology of the lithium-ion diffusion network as well as the connectivity of the non-diffusing framework strongly affect lithium-ions diffusion in oxide materials. Structural features that allow lithium superionic conductivity in oxide materials are identified, which led to the discovery of 16 novel fast lithium-ion conducting frameworks. In the second part of the talk, we present our statistical framework for understanding the correlation between anion-group rotational motion and lithium-ion translational motion. Using event-detection algorithms on long ab-initio molecular dynamics trajectories, we detect and differentiate various types of rotational motion of anion groups. This allows us to obtain a statistically rigorous understanding of how each type of anion group rotational motion affects lithium-ion diffusion events. These fundamental understandings provide design guidelines towards the development of fast-diffusing inorganic materials optimal for all-solid-state batteries.