Architecting 3D Space‐Charge Heterointerfacial Networks for Electrode‐Scale Ion Transport

Harnessing space‐charge effects to govern carrier dynamics is central to nanoionics, yet translating localized nanoscale transport into continuous electrode‐wide percolation remains challenging. Here, we report an architectural strategy that uses Na 2 O/Na 2 CO 3 heterointerfaces as local nanoionic transport units and organizes them into a bulk‐distributed, three‐dimensional network throughout a preformed electrode. This architecture is realized by coupling ultralow‐flux Na‐vapor metallization with mesopore‐regulated gas‐solid conversion in a preformed metal‐organic framework (MOF) host. The synergy of space‐charge carrier enrichment and MOF‐mediated lattice distortion simultaneously boosts carrier density and lowers migration barriers, yielding an estimated local interfacial conductivity on the order of 10 −7 S cm −1 at 25°C, from intrinsically insulating Na 2 O (10 −12 S cm −1 ) and Na 2 CO 3 (10 −23 S cm −1 ). Integrated with conducting carbon, this functionally percolating network enables stable solid‐state presodiation and ultrahigh‐rate sodium‐ion full cells. This work bridges the gap between nanoscopic interface physics and macroscopic device functionality, identifying the spatial connectivity of phase boundaries, rather than the localized space‐charge effect alone, as a programmable design variable for next‐generation solid‐state ionics.