Researchers at UCLouvain (Belgium), in collaboration with scientists from Marburg University, the Technical University of Münich, the Technical University of Graz, and Toyota have discovered a new solid-state fast ionic conductor—LiTi₂(PS₄)₃ or LTPS—that exhibits a Li-ion diffusion coefficient (a direct measure of lithium mobility) about an order of magnitude higher than that of current state-of-the-art Li superionic conductors (Li₁₀GeP₂S₁₂).

A paper on their discovery is published in the journal Chem.

Solid-state materials with high ionic conduction are necessary for many technologies, including all-solid-state lithium (Li)-ion batteries. The move to solid state batteries offers a number of advantages, including safety, but lithium ions in solids are less mobile than in liquids. This lower mobility limits the battery performance in terms of charge and discharge rate.

Understanding how crystal structure dictates ionic diffusion is at the root of the development of fast ionic conductors, the researchers said, noting that LTPS’ lithium mobility comes directly from its unique crystal structure (i.e., the arrangement of atoms).

… 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.

—Di Stefano et al.

The researchers need further study and to improve the material to enable its future commercialization. Toyota supported the study scientifically and financially. A patent has been filed listing the UCLouvain researchers as inventors.

Resources

• Davide Di Stefano, Anna Miglio, Koen Robeyns, Yaroslav Filinchuk, Marine Lechartier, Anatoliy Senyshyn, Hiroyuki Ishida, Stefan Spannenberger, Denise Prutsch, Sarah Lunghammer, Daniel Rettenwander, Martin Wilkening, Bernhard Roling, Yuki Kato, Geoffroy Hautier (2019) “Superionic Diffusion through Frustrated Energy Landscape” Chem doi: 10.1016/j.chempr.2019.07.001