Ce/O Co‐Substitution Strategy Enhanced Stability of Sulfide Electrolyte for All‐Solid‐State Lithium Metal Batteries

Sulfide solid electrolytes (SSEs) exhibit exceptional ionic conductivity and processing advantages for all-solid-state lithium metal batteries (ASSLBs), but their commercialization is constrained by ambient hydrolysis-induced H₂S generation and lithium dendrite formation at electrolyte/anode interfaces. Herein, a Ce/O co-substitution strategy is employed to synthesize argyrodite-type Li_5.4+xP_1-xCe_xS_4.4-2xO_2xCl_1.6 (0 ≤ x ≤ 0.05) solid electrolytes. The substitution of P⁵⁺ with Ce⁴⁺ and S^2- with O^2- in the PS₄ ^3- structure forms stable CeS₄ ^4- and PS₃O^3- groups and enhances structural integrity. Simultaneously, the incorporation of Ce⁴⁺ expands the lattice spacing and facilitates Li⁺ transport. Optimized Li_5.42P_0.98Ce_0.02S_4.36O_0.04Cl_1.6 electrolyte exhibits superior ionic conductivity (7.13 mS cm^-1) and excellent air stability (H₂S emission: 0.36 cm³ g^-1 after 30 min in 30% RH). The electrolyte demonstrates an enhanced critical current density of 1.3 mA cm^-2 and stable lithium plating/stripping over 5000 h at 0.1 mA cm^-2. ASSLBs with LiNbO₃@NCM622 cathodes deliver an initial discharge capacity of 128.19 mAh g^-1 and 99.49% retention after 300 cycles. This work provides a Ce/O co-substitution strategy for designing high-performance SSEs toward practical all-solid-state lithium metal batteries.