Engineering high-performance argyrodite sulfide electrolytes via metal halide doping for all-solid-state lithium metal batteries

Abstract

Solid-state electrolytes (SSEs) play a crucial role in the operation of all-solid-state lithium metal batteries (ASSLMBs). Among them, sulfide SSEs have attracted particular attention due to their high ionic conductivity. However, the incompatibility of sulfide SSEs with lithium anodes and the inherent air instability severely impact battery cycling performance. Here, we successfully synthesize halogen-rich lithium argyrodites with the general formula Li_{5.5 + 3x}P_1−xCu_xS_4.5Cl_{1.5 − 2x}Br_2x. The incorporation of Cu and Br alter the spatial arrangement and electronic distribution of structure. Given that the anion disorder positively affects Li-ion dynamics, the ultrahigh ionic conductivity of 10.3 mS cm⁻¹ at room temperature has been achieved in Li_5.8P_0.9Cu_0.1S_4.5Cl_1.3Br_0.2 (LPSC-CB). Importantly, benefiting from the robust and stable interlayer, the lithium symmetric batteries deliver prolonged plating/stripping over 3000 h at 0.2 mA cm⁻². Furthermore, the density functional theory calculations were used to prove the mechanisms of high chemical stability. Notably, the LPSC-CB electrolyte has remarkable applicability in ASSLMBs. The full batteries of FeS₂/LPSC-CB/Li deliver outstanding discharge-specific capacities of 788.9 mAh g⁻¹ and robust cycling stability (>4.02 mAh cm⁻² after 200 cycles). The versatile CuBr₂ substitution in the most promising argyrodite electrolytes is considered as a valid strategy to realize high ionic conductivity and air-stabilized sulfide SSEs for large-scale applications.