Soft-carbon-induced interfacial stabilization and pore reconstruction of anthracite-derived hard carbon for advanced sodium-ion batteries

Hard carbon (HC) is considered one of the most promising anode materials for sodium-ion batteries (SIBs) owing to its abundant sodium-storage sites and excellent cycling stability. However, excessive surface defects and open-pore structures in HC usually induce continuous electrolyte decomposition, unstable solid electrolyte interphase (SEI) formation, and low initial Coulombic efficiency (ICE). Herein, a synergistic strategy combining pre-oxidation treatment with oleic-acid (OA)-derived soft-carbon coating is proposed to simultaneously regulate pore structure and interfacial chemistry in anthracite-derived hard carbon. The pre-oxidation process disrupts the highly ordered aromatic structure of anthracite and promotes the formation of cross-linked disordered carbon frameworks, while the OA-derived soft carbon uniformly coats the hard-carbon surface, forming a unique “hard-carbon core/soft-carbon shell” architecture. Structural analyses reveal that the soft-carbon coating partially transforms open pores into closed or semi-closed pores and simultaneously induces the formation of a thin, dense, and homogeneous SEI layer. Benefiting from the synergistic effects of pore reconstruction and interfacial stabilization, the optimized 1.5OA-OHC electrode delivers a high reversible capacity of 293.16 mAh g −1 and an enhanced ICE of 78.21%. Mechanistic investigations further demonstrate that the ordered soft-carbon coating effectively suppresses excessive electrolyte decomposition, accelerates Na + desolvation and transport kinetics, and promotes reversible sodium storage within closed pores. This work provides an effective strategy for simultaneously engineering pore structure and interfacial chemistry toward low-cost and high-performance hard-carbon anodes for next-generation sodium-ion batteries.