Superionic diffusion through frustrated energy landscape

TL;DR

This paper demonstrates that LiTi2(PS4)3 has a significantly higher lithium-ion diffusion coefficient due to its unique frustrated energy landscape, which resembles liquid-like behavior and enhances ionic mobility.

Contribution

It reveals how a frustrated crystal structure without regular sites can create a liquid-like energy landscape, leading to superior ionic diffusion in solid-state materials.

Findings

LiTi2(PS4)3 exhibits an order of magnitude higher diffusion coefficient.

The crystal structure lacks regular tetrahedral or octahedral sites.

Frustrated energy landscape results in low activation energy and high pre-factor.

Abstract

Solid-state materials with high ionic conduction are necessary to many technologies including all-solid-state Li-ion batteries. Understanding how crystal structure dictates ionic diffusion is at the root of the development of fast ionic conductors. Here, we show that LiTi2(PS4)3 exhibits a Li-ion diffusion coefficient about an order of magnitude higher than current state-of-the-art lithium superionic conductors. We rationalize this observation by the unusual crystal structure of LiTi2(PS4)3 which offers no regular tetrahedral or octahedral sites for lithium to favorably occupy. This creates a smooth, frustrated energy landscape resembling more the energy landscapes present in liquids than in typical solids. This frustrated energy landscape leads to a high diffusion coefficient combining low activation energy with a high pre-factor.