Regulating Sodium Deposition Kinetics: A MgF ₂ @Graphene Fibers Host for Wide‐Temperature Sodium Metal Batteries

ABSTRACT Stable operation under harsh conditions remains challenging for sodium metal batteries (SMBs) due to large volume expansion, sluggish transport kinetics, and dendrite growth. In this study, a sodophilic host material consisting of MgF 2 nanoparticles embedded within fluorine‐rich graphene fibers (MgF 2 @GF) is successfully synthesized through chemical vapor deposition with in situ fluorination. During the initial Na plating process, MgF 2 nanocrystals undergo an in situ electrochemical conversion to form metallic Mg and NaF. The generated metallic Mg serves as sodiophilic nucleation seeds to promote uniform sodium deposition, while the robust NaF‐rich protective layer prevents unnecessary side reactions, thereby synergistically inhibiting the growth of sodium dendrites. Meanwhile, the porous, F‐doped GF framework offers a buffering space for Na deposition, enhancing cycling stability. Multi‐scale analysis, including theoretical calculations and finite element simulations, are employed to systematically reveal the mechanisms behind the enhanced sodium deposition behavior. The fabricated MgF 2 @GF symmetric cell demonstrates long‐term stable cycling exceeding 1500 h with low overpotential. When paired with Na 3 V 2 (PO 4 ) 2 O 2 F cathode, the full cell exhibits good thermal stability at 40°C and maintains a reversible capacity of 93 mAh g −1 at −15°C with 92.1% capacity retention. This study offers new insights into the design of high‐performance SMBs.