Structural insights into BH4- and Cl-co-substituted argyrodite solid electrolytes for superior ionic conductivity

Abstract

All-solid-state batteries (ASSBs) with solid electrolytes offer the potential for higher energy density and improved safety compared to conventional Li-ion batteries. Among solid electrolytes, sulfide-based materials have gained considerable attention due to their excellent ionic conductivity and ease of fabrication. This study focuses on the synthesis and characterization of BH4- and Cl- co-substituted argyrodite solid electrolytes to achieve enhanced Li-ion conductivity. The synthesized electrolytes exhibited exceptional ionic conductivity, reaching 15.1 mS cm- 1. Partial substitution of BH4 sites in the Li argyrodite structure with Cl- introduced anion mixing, significantly improving ionic conductivity. The structural and compositional effects of Cl-incorporation were investigated using Raman and solid-state nuclear magnetic resonance spectroscopies. These techniques identified the thiophosphate local structure and localized the prominent PS4 3- units within the synthesized electrolytes. A strong correlation was observed between the total proportion of the argyrodite phase in terms of the PS4 3- units and ionic conductivity. Furthermore, the synthesized electrolytes were tested in ASSBs featuring a Li-In anode and a high-Ni layered cathode, demonstrating superior rate performance and cycling stability.