Tailoring Local Anion Chemistry Affinity Enables Stable Halide-Sulfide Interfaces and Fast Ion Transport in...

All-solid-state batteries (ASSBs) employing halide/sulfide bilayer electrolytes offer a promising route toward high energy density by combining the high oxidative stability of halides with the superior reductive stability of sulfides. However, severe halide-sulfide interfacial incompatibility induces continuous interfacial degradation and undermines Li⁺ transport. Unlike conventional interfacial engineering approaches that rely on coatings or artificial buffer layers, we report a local chemistry-driven intrinsic compatibility strategy that fundamentally stabilizes halide-sulfide interfaces. By sulfurizing amorphous halide electrolytes Li₂O-TaCl₅, the short-range coordination chemistry and medium-range topology are simultaneously reconstructed, in which sulfur-rich local motifs become thermodynamically more resistant to further sulfur substitution, whereas sulfur-containing medium-range networks exhibit stronger binding with PS₄ units in Li₆PS₅Cl, thereby intrinsically stabilizing the halide-sulfide interface and suppressing interfacial decomposition. Simultaneously, the sulfurized framework exhibits enhanced structural heterogeneity and interconnected Li⁺ migration pathways, achieving an ultrahigh ionic conductivity of 14.2 mS cm^-1. As a result, the assembled NCM89|8S-LTOC|LPSC|Li-In ASSBs exhibit outstanding electrochemical performance from -50°C to 100°C, including 131 mAh g^-1 at -50°C, 2000-cycle stability at 15 C, and high areal capacities up to 21.7 mAh cm^-2. This work highlights local anion chemistry regulation as an effective strategy for developing robust halide-sulfide ASSBs.