Heterogeneous nucleation strategy toward ordered hard carbon surface enriched in carbonyls for sodium-ion batteries

Hard carbon stands as one of the most promising anode materials for sodium-ion batteries (SIBs). While, the practical application has been severely limited by low initial Coulombic efficiency (ICE) and sluggish kinetics arising from uncontrolled surface side reactions. Herein, a novel heterogeneous nucleation-engineered surface reconstruction strategy was proposed to create an ordered, carbonyl-enriched surface on the hard carbon microspheres. Distinct from conventional coating methods, this approach achieved the synthesis of core-shell spherical hard carbon by precisely regulating the nucleation mode of raw materials in the solution. The as-prepared material delivered excellent electrochemical performance, achieving an ICE of over 91% with a reversible capacity of 364 mAh g⁻¹ in the ether-based electrolytes, and an ICE exceeding 85% with a capacity over 370 mAh g⁻¹ in the ester-based electrolytes. Comprehensive characterization combined with theoretical calculations elucidated that the surface carbonyl groups, generated via heterogeneous nucleation, played a dual role in suppressing the decomposition of organic solvent components and accelerating adsorption kinetics of Na⁺. This work provided a transformative interfacial engineering perspective for designing high-efficiency hard carbon anodes for next-generation energy storage.