Tailoring Local Anion Chemistry Affinity Enables Stable Halide–Sulfide Interfaces and Fast Ion Transport in Dual‐Electrolyte all‐Solid‐State Batteries

ABSTRACT 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 Li 2 O–TaCl 5 , 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 PS 4 units in Li 6 PS 5 Cl, 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.