Programmable Steric-Enhanced Dual-Crosslinking Preoxidation Unlocks Closed-Pore Dominated Sodium Storage in Pitch-Derived Carbon Anodes

Pitch is an ideal hard carbon precursor for sodium-ion batteries (SIBs) owing to its abundant availability, low cost, and high carbon yield, yet its pronounced graphitization tendency during carbonization limits sodium storage capacity. To address this, a Steric-Enhanced Dual-Crosslinking (SEDC) preoxidation strategy is developed by integrating multifunctional organophosphorus molecules (e.g., phytic acid) during air preoxidation. The SEDC mechanism synergistically combines two concurrent pathways: (i) steric hindrance induced by multifunctional organophosphorus groups, which utilize their voluminous molecular structures to suppress π–π stacking, and (ii) dual-crosslinking via inherent oxygen-functionality bonding (from air preoxidation) and phosphate-group condensation reactions among organophosphorus molecules. This synergy expands interlayer spacing to 0.390 nm, generates pseudo-graphitic domains with abundant closed nanopores, and maximizes pore-filling-dominated Na⁺ storage. The optimized anode delivers outstanding performance: a reversible capacity of 378.4 mAh g⁻¹ with 68.5% plateau-capacity contribution and 90% initial Coulombic efficiency, surpassing most state-of-the-art pitch-derived carbons. Critically, systematic extension to other organophosphorus systems with graded P-functionality (3–6) validates universality—higher functionality strengthens crosslinking, amplifies disorder/closed-pore density, and elevates electrochemical metrics. Thus, this approach establishes a universal platform for molecularly tailored synthesis of high-performance pitch-derived hard carbon anodes through programmable crosslinking design.