Ultra-Sodiophilic Mixed Conductor Interphase Enabling Uniform Top Deposition for Quasi-Solid-State Sodium-Metal Batteries

Artificial solid electrolyte interphase offers a promising route to improve the lifespan and safety of quasi-solid-state sodium-metal batteries (QSMBs), yet its limited ion conductivity and the low liquidity of the polymer electrolyte often result in unstable Na plating/stripping kinetics and poor interfacial durability. Herein, we propose a surface-induced “top” Na deposition mechanism facilitated by an ultra-sodiophilic ionic/electronic mixed conductor interphase exhibiting strong Na⁺ adsorption affinity, which ensures fast and dendrite-free Na anode operation. The embedded Na₃Sb alloy phase, featuring high electronic conductivity and strong Na⁺ adsorption energy, significantly accelerates interfacial ion diffusion and nucleation kinetics, forming a smooth and compact Na deposition layer that facilitates stable solid electrolyte interphase formation and preserves interfacial integrity. Consequently, Na||Na symmetric cells employing a 1, 3-dioxolane-based gel polymer electrolyte deliver an ultra-long-cycling lifespan of 1000 h at 0.5 mA cm⁻² with a low overpotential of 40 mV. Moreover, QSMBs incorporating the modified Na anode and Na₃V₂(PO₄)₃ cathode demonstrate outstanding cycling stability (74.1% capacity retention after 9000 cycles at 2C) and superior rate capability (91.7 mAh g⁻¹ at 5C). The work provides mechanistic insights and practical strategies for regulating Na deposition, paving the way toward high-performance QSMBs. (Figure presented.)