Insights into the chemical and electrochemical behavior of halide and sulfide electrolytes in all-solid-state batteries†

Conventional lithium-ion batteries (LIBs) have become widely used in small and large applications, but the use of toxic and flammable liquid electrolytes can lead to safety issues and reduced cell performance. New generation solid-state lithium batteries (SSBs) have the potential to replace LIBs due to their safety and potentially high energy density (>450 W h kg⁻¹). The solid electrolyte (SE) is a crucial component in solid-state batteries. Among the available options, sulfide- and halide-based solid electrolytes stand out as promising candidates due to their high ionic conductivity and ease of processing. They are among the most prominent topics in solid electrolyte research for solid-state batteries. Despite their advantages like good compatibility with high-voltage cathodes and easy manufacturing, solid electrolytes still face issues of degradation of the Li metal/solid electrolyte interface. This is due to the formation of side reaction products at the interface, which inhibits lithium transport across it. The primary issue stems from the poor chemical and electrochemical stability of sulfide- and halide-based solid electrolytes when in contact with lithium metal. In this study, we have demonstrated that the composite electrolytes (Li₃YCl₄Br₂:Li₆PS₅Cl) comprising halide and argyrodite can prevent the formation of unfavorable interactions between the solid electrolyte and the Li metal anode. The Li/Li-symmetric cells employing the Li₃YCl₄Br₂:Li₆PS₅Cl electrolytes exhibited enhanced cycle life and high critical current density (CCD) from C/20 to C/2, compared to the symmetric cells utilizing only Li₃YCl₄Br₂ or Li₆PS₅Cl electrolyte. Furthermore, the Li/Li₃YCl₄Br₂/NCM half-cells demonstrated high initial coulombic efficiency and extended cycle life compared to half-cells utilizing traditional halide and argyrodite electrolytes. The approach described here offers a pathway to enhance halide-based solid-state batteries, providing a relatively simple and effective strategy.