Solid-state materials with extremely high ionic diffusion are necessary to many technologies including all-solid-state Li-ion batteries. Despite the strong efforts made towards the search for crystal structures leading high lithium diffusion, very limited number of compounds showing superionic diffusion are known and clear materials design principles are greatly sought for.
In this work, we demonstrate that LiTi2(PS4)3 exhibits the largest Li-ion diffusion coefficient ever measured in a solid. We use extensive characterisation (neutron, X-ray diffraction, impedance and NMR) as well as theoretical studies and rationalise the exceptional performances of this new superionic conductor through the concept of frustrated energy landscape. The absence of regular and undistorted lithium site to occupy leads to low energy barrier for diffusion as well as an exceptional pre-factor. Our work not only shines light on a new family of superionic conductors but offers a new design principle for discovering new ones.