Bifunctional crosslinking-induced structural engineering towards improved sodium storage in pitch-derived hard carbon

Abstract

The construction of crosslinking structures in pitch-derived carbons is essential for disrupting intrinsic π-π stacking and achieving high performance sodium-ion batteries. However, the structural collapse caused by the pyrolysis-oxidation kinetic mismatch and the challenge of rational crosslinker selection remain significant obstacles. Herein, we introduce a bifunctional crosslinking agent that simultaneously accelerates oxidative ring-opening and reinforces covalent network formation, thereby overcoming the kinetic imbalance between oxidation and pyrolysis. Specifically, 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) not only promotes generating oxygen-free radicals due to the low bond energy of its C–O bonds but also reacts with oxygen-containing functional groups in oxidized pitch to form covalent linkages, thereby further increasing crosslinking density. Consequently, the resulting hard carbons exhibit expanded interlayer spacing (d₀₀₂) and a defect-rich hierarchical porous structure. This gives rise to high reversible capacity (328.32 mAh g⁻¹), excellent rate capability (171.54 mAh g⁻¹ at 400 mA g⁻¹), and outstanding cycling stability (93.4% capacity retention after 200 cycles at 40 mA g⁻¹). Moreover, its practical feasibility is demonstrated in full cells. This work establishes a robust paradigm for developing next-generation hard carbon anodes by synergistically optimizing the bonding configuration of precursors, pore architecture, and carbon framework, while offering deep mechanistic insight into the pitch crosslinking process.