Hyper-Crosslinking to Customize Ultrathin-Wall Closed Pores in Pitch-Derived Carbon for Sodium-Ion Batteries

Pitch is a highly preferable and cost-effective precursor of carbon materials. Nevertheless, its direct pyrolysis typically yields highly graphitized soft carbon, posing challenges to the modulation of closed-pore architecture, due to intense intermolecular π-π interactions. This results in a negligible plateau capacity and sluggish diffusion kinetics in sodium-ion batteries (SIBs). In this study, an innovative hyper-crosslinking strategy is proposed to reconstruct pitch molecularly and precisely tailor the closed-pore structure of the derived carbon. The crosslinker intertwined the pitch units, transforming the linear molecules into 3D porous polymers. Structurally, these 3D cavities tactfully reserved space for forming closed-pore cores, with the single-layer pitch network skeleton transforming into ultrathin pore walls upon carbonization. This strategy enabled the disruption of intense π-π interactions and, therefore, inhibited structural ordering, facilitating a structure transition from graphitic soft carbon to highly-disordered carbon with abundant closed pores featuring appropriate pore sizes (2 nm) and ultrathin pore walls (1-2 layers). The optimal sample delivered a high capacity of 370 mAh g^-1 at 30 mA g^-1, as well as a rate capability that surpassed those of most previously reported pitch-derived carbons. Hyper-crosslinking has advanced the development of low-cost and high-performance carbon materials for large-scale energy storage.