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

Abstract 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 0.7 Co 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||Na 3 V 2 (PO 4 ) 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.