Symmetry-Engineered Carbon Scaffold for Interface-First Sodium-Sulfur Batteries

Room-temperature sodium-sulfur (RT Na─S) batteries offer high theoretical energy density (1274 Wh kg^-1) and low-cost, abundant materials, making them promising for large-scale energy storage. However, commercialization is hindered by multiple challenges: polysulfide shuttling and sluggish kinetics at the cathode, coupled with dendrite growth and interfacial failure at the anode. Here, an oxygen-doped carbon fiber (OCF) framework is designed and employed as a bifunctional host within a symmetric all-carbon-fiber cell architecture to simultaneously address these issues. The 3D porous OCF framework chemically anchors polysulfides, catalyzes their redox reactions, and guides uniform sodium nucleation/deposition. This synergy suppresses polysulfide shuttling and dendrite growth. Performance tests demonstrate an extremely low Na nucleation overpotential (27 mV at 1 mA cm^-2) and stable, dendrite-free cycling exceeding 3600 h. In full Na─S cells, this design delivers a specific capacity of 753 mAh g^-1 after 200 cycles at 0.2 C, retains ≈85% capacity after 2000 cycles at 0.5 C, and exhibits excellent rate performance (5 C). Mechanistic studies reveal OCF enhances Na⁺ transport and interfacial kinetic stability. This work presents a generalizable, interface-first design paradigm for safe, long-lasting, low-cost Na─S batteries free from shuttling and dendrites.