Moving Beyond 99.9% Coulombic Efficiency for Anode‐Free Sodium Metal Battery

Anode‐free sodium metal batteries (AFSMBs) are promising for high‐energy‐density storage but face challenges such as uneven sodium deposition and dendrite growth. This study develops a three‐dimensional host material consisting of iron‐anchored carbon nanotubes (CNT‐Fe) through in‐situ thermal reduction. Combined with density functional theory calculations and multiphysics simulations, we demonstrate that the sodiophilic Fe nanoparticles significantly reduce Na adsorption energy (–1.757 eV vs. –0.74 eV for Cu) and promote uniform charge distribution on the electrode. The CNT‐Fe@Cu current collector achieves an ultralow nucleation overpotential of 7.6 mV and maintains 99.9% Coulombic Efficiency for 1100 cycles in half‐cells. Na//CNT‐Fe@Cu||Na//CNT‐Fe@Cu symmetric cells exhibit outstanding stability over 2900 h, while CNT‐Fe@Cu||NVP anode‐free full cells retain 84.3% capacity after 150 cycles with 10 mg cm −2 cathode loading. This work establishes a viable strategy for leveraging carbon‐based materials toward high‐performance AFSMBs.