Superionic Diffusion through Frustrated Energy Landscape

Solid-state materials with high ionic conduction are necessary for many technologies, including all-solid-state lithium (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 that of current state-of-the-art Li superionic conductors. We rationalize this observation by the unusual crystal structure of LiTi2(PS4)3, which offers no regular tetrahedral or octahedral sites for Li to favorably occupy. This creates a smooth, frustrated energy landscape resembling the energy landscapes present in liquids more than those in typical solids. This frustrated energy landscape leads to a high diffusion coefficient, combining low activation energy with a high pre-factor.