Dual-functional enhancement of argyrodite solid electrolytes with borohydride for high ionic conductivity and lithium metal compatibility via AgCl addition

Abstract

All-solid-state batteries (ASSBs) employing sulfide-based solid electrolytes and Li metal anodes offer superior safety and high energy density. Among the various sulfide-based electrolytes, Li argyrodite solid electrolytes incorporating borohydride have attracted significant attention due to their high ionic conductivities, making them strong candidates for practical applications. However, their limited stability against Li metal remains a major obstacle to the advancement of ASSBs. In this study, we propose a dual-functional strategy by introducing silver chloride (AgCl) into borohydride-containing argyrodite solid electrolytes. This approach simultaneously enhances ionic conductivity via Cl⁻ substitution and improves interfacial stability with Li metal through the formation of reduced Ag particles. The optimized composition achieved a high ionic conductivity of 13.3 mS cm⁻¹ and a critical current density of 2.9 mA cm⁻² at 30 °C. Comprehensive analyses confirm that AgCl decomposes during synthesis, enabling Cl⁻ ions to substitute into halide sites within the argyrodite framework, while metallic Ag particles are dispersed throughout the solid electrolyte matrix. These Ag particles form a Li–Ag alloy at the interface, which effectively suppresses Li dendrite growth and mitigates decomposition of the solid electrolyte. ASSBs incorporating the Ag-distributed solid electrolyte demonstrated improved rate capability and cycling stability. This dual-functional design presents a promising direction for enhancing both the performance and longevity of ASSBs.