Zn substituted Li4P2S6 as a solid lithium-ion electrolyte for all-solid-state lithium batteries

Li-ion conductors are pivotal materials for all-solid-state Li batteries requiring high energy densities and operational safety. PS4-based thio-phosphate materials have been intensively investigated as solid electrolytes; however, studies on more stable P2S6-based materials are scarce. We herein report on the application of Zn-substituted Li4P2S6, Li4-2xZnxP2S6, as a Li-ion conductor. Owing to the slightly smaller ionic radius of Zn2+ than Li+, the unit cell volume decreases gradually upon Zn substitution without introducing significant structural changes. However, the ionic conductivity of the substitution phase was improved by 104 times (3.8 x 10-6 S cm-1) at x = 0.75 compared to unsubstituted Li4P2S6, which was achieved by generating deficiency on the Li sites via substitution. Such Li-ion deficient site enables Li ions to hop from one site to another in the crystal structure. The 3D diffusion pathway analysis using bond-valence-landscape-energy calculations suggests that the Li diffusion pathways are mostly two-dimensional in the ab plane in this structure. This study shows that an appropriate Li defect concentration within a given structure is critical to improving ionic conductivity.

Automated summary

This study reports on the application of Zinc-substituted Li4P2S6 as a Li-ion conductor, which showed significantly improved ionic conductivity compared to unsubstituted Li4P2S6. The improvement was achieved by generating Li-ion deficiency through Zn substitution, enabling Li ions to hop within the crystal structure. The diffusion pathways of Li ions were found to be mostly two-dimensional in this structure.