Chemical Integration of Multiphase Interfaces in All-Solid-State Sodium–Oxygen Batteries via Monolithic Ceramic Scaffolds

The advancement of all-solid-state sodium-oxygen (Na-O₂) batteries is fundamentally constrained by the formidable chemo-mechanical and kinetic barriers at solid-solid interfaces. Herein, we report a high-performance, room-temperature all-solid-state Na-O₂ battery enabled by a monolithic bilayer β-Al₂O₃ architecture that redefines interfacial charge transfer through a dual-interface integration strategy. By constructing an integrated porous-dense scaffold, we eliminated the macroscopic physical boundaries between the electrolyte and cathode, establishing a seamless, low-resistance ionic conduction continuum. Specifically, a conformal, 30 nm thick graphitic carbon layer was deposited within the cathodic framework via plasma-enhanced chemical vapor deposition, creating a high-fidelity electronic network that maximizes active site utilization. On the anode side, we introduced a reactive wetting mechanism mediated by Bi₂O₃ nanosheets. The in situ chemical reconfiguration and alloying reaction at the interface generate a gradient Na-Bi-O mixed-conducting interphase, effectively fusing the sodium metal to the ceramic electrolyte and ensuring stable long-term cycling (>14,000 h for symmetric cells). Consequently, the battery delivers an unprecedented discharge capacity of 4012 mA h g^-1 at room temperature with an exceptional reversibility. Operando Raman spectroscopy and differential electrochemical mass spectrometry reveal that the solid-state environment provides a unique kinetic stabilization for the metastable NaO₂ phase, suppressing the parasitic disproportionation pathways common to liquid systems. This work provides a universal blueprint for engineering chemically integrated interfaces in complex multiphase all-solid-state energy chemistry.