Heterogeneous Interfacial Layers Derived from the In Situ Reaction of CoF2 Nanoparticles with Sodium Metal for Dendrite‐Free Na Metal Anodes

Abstract Sodium‐metal batteries, with high energy density and low cost, are emerging stars in the field of large‐scale energy storage and power batteries. The application of sodium metal is hindered by side reactions between the active sodium metal anode and the electrolyte, unstable solid electrolyte interphase, and dendrite growth caused by the uneven distribution of sodium ions. Here, heterogeneous interface layer composed of the sodium fluoride and metallic cobalt (NaF/Co) is constructed in situ and spontaneously by introducing the CoF 2 nanoparticles confined in carbon to the Na metal surface. The NaF/Co artificial interface layer with high Young's modulus, high Na + conductivity, high surface energy, and strong sodiophilicity renders the Na + evenly distributed, suppresses Na‐dendrite growth, and reduces side reaction with electrolyte. Due to these virtues, the Na||Na symmetric cells with NaF/Co interface layers demonstrate long cycle life (1000 h at 1.0 mA cm −2 , 1.0 mAh cm −2 ). Moreover, when the NaF/Co/Na anode is matched with Na 3 V 2 (PO 4 ) 3 cathode, the produced full battery (Na 3 V 2 (PO 4 ) 3 ||NaF/Co/Na) exhibits a long lifespan of 1000 cycles at 15 C and a high‐rate capacity of ≈52 mAh g −1 at 60 C. This work provides a new strategy to solve the dendrite growth of Na metal anodes.