Highly Sodiophilic, Defect-Rich, Lignin-Derived Skeletal Carbon Nanofiber Host for Sodium Metal Batteries

Three-dimensional host structures with superior sodiophilicity and low nucleation barriers can help combat the complex failure modes of Na metal anodes originating from accelerated dendrite formation, anodic corrosion, and electrolyte depletion. This work reports the fabrication of a unique super-sodiophilic, defect-rich and hierarchically porous skeletal carbon nanofiber (SCNF) host for SCNF@Na anodes using electrospinning of the low-cost, renewable lignin biopolymer. The uniform nucleation and plating of Na effectuated by the hierarchically porous structure coupled with the defect-induced formation of a resilient, F-rich solid electrolyte interface (SEI) layer offers excellent protection to the metallic anode. The defect-rich porous structure plays an important role in mediating dense Na nucleation, planar growth, and electrochemical stability according to the depth profiling experiments and density functional theory calculations. The SCNF@Na composite anode maintains high Coulombic efficiencies (CEs) and electrochemical reversibility in asymmetric and symmetric cells. The full cells prepared by interfacing the SCNF@Na anode with a Na₃V₂(PO₄)₂F₃ cathode delivers exceptional capacity retention of 106 mAh g^–1 for 350 cycles with an average CE of 99.2% at 1C, and 103 mAh g^–1 after 200 cycles at 4C. Such rationally designed carbon hosts derived from biopolymers open a new avenue for safe and low-cost metal batteries.