Boosting the Reversibility of Sodium Metal Anode via Heteroatom-Doped Hollow Carbon Fibers.

Sodium (Na) metal anodes stand out with their remarkable capacity and natural abundance. However, the dendritic Na growth, infinite dimensional changes, and low Coulombic efficiency (CE) present key bottlenecks plaguing practical applications. Here, heteroatom-doped (nitrogen, sulfur) hollow carbon fibers (D-HCF) are rationally synthesized as a nucleation-assisting host to enable a highly reversible Na metal. The "sodiophilic" functional groups introduced by the heteroatom-doping and large surface area (≈1052 m2 g-1 ) synchronously contribute to a homogenous plating morphology with dissipated local current density. High "sodiophilicity" of the D-HCF is confirmed by first-principle calculations and experimental results, where strong adsorption energy of -3.52 eV with low Na+ nucleation overpotential of 3.2 mV at 0.2 mA cm-2 is realized. As such, highly reversible plating/stripping is achieved at 1.0 mA cm-2 with average CE approximating 99.52% over 600 cycles. The as-assembled Na@D-HCF symmetric cells exhibit a prolonged lifetime for 1000 h. A full-cell paired with Na3 V2 (PO4 )3 cathode further demonstrates stable electrochemical behavior for 200 cycles at 1 C along with excellent rate performance (102 mAh g-1 at 5 C). The results clearly show the effectiveness of the D-HCF in manipulating Na+ deposition and thus the significance of nucleation control in realizing dendrite-free metal anodes.