Reconstructing the Spatial State of the Precursor Chain Segment to Obtain a Hard Carbon Anode with High Platform Capacity for Sodium Ion Batteries

Closed pores play a critical role in enhancing the sodium storage capacity of hard carbon (HC) anodes, and regulation of the closed pore structure is regarded as one of the most effective strategies for improving the electrochemical performance of sodium-ion batteries (SIBs). However, in polymer-derived HCs, the mechanism of closed pore formation and effective regulation strategies at the molecular level remain unclear. In this study, we propose, based on experimental data and theoretical calculations, that the introduction of phenyl π–π stacking effects not only increases the rigidity of the precursor framework by creating additional entanglement sites within the precursor chains but also restricts the occurrence of chain disentanglement during high-temperature carbonization, thereby promoting the formation of the pseudographitic phase and closed-pore structures in hard carbon microcrystals. As a result, the optimized HC anode achieves a reversible specific capacity of up to 410.5 mA h g –1 at 0.02 A g –1, while also demonstrating exceptional cycling stability, with a capacity retention rate of 88.6% after 800 cycles at 1 A g –1 . This study provides a perspective on elucidating the mechanism of closed pore formation at the molecular level.