Synergistic Regulation of Sodium Metal Deposition Pattern Through Three-Dimensional Sodiophilic Gradient ZnO/Fe0.7Co0.3 Frameworks and Magnetic Fields for High-Performance Sodium Metal Batteries

The application of sodium metal battery is hampered by the large volume change and uncontrollable top growth of Na metal. Herein, a dual strategy including constructing a three-dimensional gradient ZnO/Fe_0.7Co_0.3 (ZFC) framework of decreasing sodiophilic capability from bottom to top, and imposing magnetic fields based on magnetohydrodynamic (MHD) effect, is proposed to regulate the sodium deposition/stripping behavior and realize the bottom-up deposition of Na. Therefore, the ZFC framework under a magnetic field of 200 mT exhibits high electrochemical reversibility with a Coulombic efficiency of 99.77 % at 1 mA cm⁻² and 1 mAh cm⁻². Meanwhile, the ZFC composite anode (ZFC@Na) with the magnetic field of 200 mT delivers a small polarization voltage of approximately10 mV and long cycle life of more than 2500 h at 5 mA cm⁻² and 5 mAh cm⁻² in symmetric cells, along with good cycle stability in ZFC@Na||Na₃V₂(PO₄)₃ full cells (200 cycles at 1 C with a high capacity retention of 98 %). Accordingly, the novel strategy of combining magnetic fields and sodiophilic gradient frameworks provides a perspective to solve the issues of sodium dendrite growth.