Unlocking Anode-Free Sodium Metal Batteries Via Solvent Co-Insertion Mediated In Situ Sodiophilic Interface Engineering

Anode-free sodium metal batteries hold significant promise for high-energy-density storage but face critical challenges related to sodium deposition dynamics and interfacial instability. Traditional approaches, such as alloy-based current collectors or fluorinated interfaces, often suffer from irreversible volume expansion or corrosive fabrication processes. This study introduces a solvent co-intercalation-mediated in situ sodiophilic interface engineering strategy to overcome these limitations. A graphitized carbon-modified aluminum current collector dynamically regulates interfacial evolution through solvated sodium-ion co-intercalation during initial cycling, prompting the formation of a C-NaF interface with ultralow Na⁺ adsorption energy. This sodiophilic interface not only facilitates uniform sodium nucleation by providing abundant sodium-philic sites but also encourages the preferential decomposition of anions in the electrolyte, leading to the creation of a robust and NaF-rich solid electrolyte interphase. Consequently, the asymmetric half-cell delivers an ultralow nucleation overpotential (9.7 mV at 0.5 mA cm⁻²) and maintains an average coulombic efficiency of 99.8% over 400 cycles at 1 mA cm⁻². When combined with a Na₃V₂(PO₄)₂O₂F (NVPOF) cathode, the full cell achieves an energy density of 363 Wh kg⁻¹ with 80% capacity retention after 250 cycles at 0.5 C. This work integrates molecular-level dynamic interfacial engineering with macroscopic electrochemical stability, providing a scalable industrial solution for next-generation battery systems.