Interfacial Electronic Structure Regulation via Dual Built‐In Electric Fields in Sulfide Solid Electrolytes

ABSTRACT Interfacial instability between sulfide solid electrolytes (SSEs) and high‐nickel layered oxide cathodes remains a fundamental bottleneck for high‐power all‐solid‐state lithium‐ion batteries, originating from uncontrolled interfacial charge transfer and electron‐induced electrolyte decomposition. Here, we report an active interfacial charge regulation strategy enabled by engineering the electronic structure at the cathode–electrolyte interface. A thin ferrielectric WO 2 Cl 2 (WOC) interlayer is introduced onto an argyrodite‐type SSE (Li 5.5 PS 4.5 Cl 0.8 Br 0.7 ), establishing a dual built‐in electric field (DBIEF) through work‐function mismatch and spontaneous polarization. This field configuration selectively anchors interfacial electrons while simultaneously lowering the Li + transport barrier, effectively decoupling ionic and electronic conduction at the solid–solid interface. Multimodal characterization and first‐principles calculations reveal suppressed electron penetration, reduced interfacial polarization, and accelerated Li + diffusion without compromising bulk ionic conductivity. As a result, all‐solid‐state cells exhibit exceptional fast‐charging durability, retaining over 83.3% capacity after 6200 cycles at 5 C, alongside stable operation under high cathode loading (26.66 mg cm −2 for more than 2000 cycles). This work establishes interfacial electronic structure engineering via built‐in electric fields as a generalizable materials design principle for stabilizing sulfide‐based solid‐state batteries beyond conventional chemical passivation strategies.