Boosting sodium storage in needle coke-derived hard carbon anode via mild ammonium persulfate activation

Needle coke features low cost, high carbon yield, and good electrical conductivity. It is considered a promising precursor for the carbon anode for sodium-ion batteries, but poor structural tunability and inferior performance limit further development. Herein, we report a facile strategy to achieve needle coke-derived hard carbon (NCAPS) with multiscale structures via activation with ammonium persulfate (APS). Systematic characterization revealed that ammonium persulfate activation introduced appropriate oxygen-containing functional groups on the surface of needle coke, while creating a turbostratic microstructure with balanced defect density and mesopores, thereby supplying abundant adsorption sites of Na⁺ and improving electrochemical performance. Benefiting from its appropriate structure and chemical composition, NCAPS exhibited a reversible capacity of 212.6 mAh g^-1 after 200 cycles at 0.2C, which was 37% higher than non-activated needle coke-derived hard carbon, and an excellent rate capability of 195.0 mAh g^-1 at 5C. We utilized APS-assisted activation to enable multiscale structural optimization, thereby significantly enhancing Na⁺ storage kinetics and electrochemical performance. Herein, we provide a mild activation approach for designing a high-performance sodium-ion battery hard carbon anode from a low-cost and highly aromatic precursor.