Lanthanum and oxygen co-doping of lithium argyrodite for enhanced humid air stability and lithium metal compatibility

Lithium argyrodite sulfide has emerged as one of the most promising solid electrolytes for all-solid-state lithium metal batteries (ASSLMBs) due to its outstanding ionic conductivity and favorable mechanical properties. However, its application is significantly hindered by issues such as poor moisture and electrochemical stability. Herein, we implement a La₂O₃ doping strategy to enhance the chemical and electrochemical stability of the Li_5.5PS_4.5Cl_1.5 electrolyte. Specifically, the large radius of La³⁺ ions induces a size effect that provides additional lithium-ion transport channels, preserving the high ionic conductivity of the original electrolyte. The introduction of O²⁻ forms stronger P-O chemical bonds, stabilizing the electrolyte structure and improving its air stability. The optimized electrolyte, Li_{5.5 + 2x}P_1-xLa_xS_4.5-1.5xO_1.5xCl_1.5 (where x = 0.04, namely LPSC-La_0.04), exhibits a remarkable room-temperature ionic conductivity of 6.23 mS cm⁻¹, a critical current density of 3.1 mA cm⁻², and stable lithium deposition/stripping behavior. The introduction of La³⁺ not only promotes uniform lithium-ion deposition but also enhances the lithium-ion transport across the passivation layer, especially at high current densities. Furthermore, the mechanical properties of the passivation layer help to suppress dendrite growth more effectively. Notably, LPSC-La_0.04 shows enhanced stability in both air and moisture environments. The material also maintains good structural stability after thermal treatment. LPSC-La_0.04-based ASSLMBs using high-nickel cathodes and Li-In anodes demonstrate a high initial discharge capacity of 179.1 mAh g⁻¹ at 1C, and a capacity retention of 83.6 % after 500 cycles. This study introduces a novel approach to simultaneously enhance the moisture and electrochemical stability of sulfide electrolytes, providing valuable insights for the development of high-performance ASSLMBs.