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

Abstract 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 H 2 S 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+x P 1−x Ce x S 4.4−2x O 2x Cl 1.6 (0 ≤ x ≤ 0.05) solid electrolytes. The substitution of P 5+ with Ce 4+ and S 2− with O 2‐ in the PS 4 3− structure forms stable CeS 4 4− and PS 3 O 3− groups and enhances structural integrity. Simultaneously, the incorporation of Ce 4+ expands the lattice spacing and facilitates Li + transport. Optimized Li 5.42 P 0.98 Ce 0.02 S 4.36 O 0.04 Cl 1.6 electrolyte exhibits superior ionic conductivity (7.13 mS cm −1 ) and excellent air stability (H 2 S emission: 0.36 cm 3 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 LiNbO 3 @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.