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 Na₂O/Na₂CO₃ 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 Na₂O (10^-12 S cm^-1) and Na₂CO₃ (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.