Oxygen-Driven Molecular Reconfiguration in Coal-Derived Hard Carbon Anodes for High-Performance Sodium-Ion Batteries

Hard carbon (HC) has emerged as a promising anode material for sodium-ion batteries (SIBs), however, it suffers from low specific capacity and inferior initial Coulombic efficiency (ICE). Herein, an oxygen-driven molecular reconfiguration strategy is proposed to strengthen reversible Na⁺ storage in HC through synergistic alkali activation and pre-oxidation. The oxygen functional groups on the surface promote the reconstruction of sp²-carbon within the highly cross-linked amorphous macromolecular coal precursor, thereby enabling the coal-based HC featuring with expanded interlayer spacing, increased pseudo-graphitic and closed-pore domains. This effectively facilitates the Na⁺ transport kinetics and stable Na⁺ (de)intercalation of HC, simultaneously suppressing the electrolyte decomposition. The resultant HC delivers a high reversible capacity of 317.4 mAh g^-1 at 25 mA g^-1, an impressive ICE of 88.05%, excellent rate capability of 253.42  mAh g^-1 at 1000 mA g^-1, and a superior capacity retention of 82.92% over 1000 cycles. This work highlights the crucial role of oxygen-driven microstructural reconstruction in durable sodium storage of HC.