Catalytic Copyrolysis Strategy for Coal-Derived Hard Carbons with Enlarged Interlayer Spacing and Closed Pores toward High-Capacity Sodium-Ion Batteries

Coal-derived hard carbon (HC) is a promising anode material for sodium-ion batteries (SIBs) owing to its low cost, abundant reserves, and high carbon yield but its practical application is hindered by the excessive formation of graphite-like microcrystals during pyrolysis, which results in poor sodium storage performance. Here, we propose a catalytic copyrolysis strategy to tailor the carbon microstructure at the molecular level. During copyrolysis, biomass-derived radicals interact with coal molecules, significantly reducing the apparent activation energy of coal pyrolysis. This catalytic effect promotes the cleavage of large aromatic ring structures in coal, decreases steric hindrance to cross-linking, and exposes more reactive sites, thereby facilitating cross-linking reactions, while gaseous byproducts further disrupt the ordered stacking of carbon layers. These cooperative effects promote the formation of disordered microcrystalline domains with enlarged interlayer spacing and abundant closed pores, thereby accelerating Na⁺ transport. The optimized HC (HC-37) achieves a high reversible capacity of 317 mAh g^-1, an initial Coulombic efficiency of 88%, excellent rate performance, and nearly 100% capacity retention after 1500 cycles at 1 A g^-1, outperforming conventional coal-derived HCs. This catalyzed pyrolysis strategy offers a facile and scalable route for tailoring coal-based carbon anodes in high-performance SIBs.