Spatial configuration engineering of phenolic resins to tune the closed pores of hard carbon for enhanced plateau-capacity sodium storage

• PF spatial engineering modulates HC closed-pore structure through aldehyde’s benzene ring variation. • RB resin with moderate benzene rings maximizes internal space through crosslinking-rigidity balance. • PF’s crosslinking-rigidity synergy limits carbon layer rearrangement to form closed pores with curved/short carbon microcrystals . • BHC demonstrates closed-pore sodium storage with 243.2 mAh g −1 plateau capacity. Tuning closed pores is crucial for achieving high-performance hard carbon (HC) anodes. However, achieving effective modulation of closed pores in phenolic resin (PF)-derived HC remains a significant challenge at the molecular level. Herein, a spatial configuration strategy based on PF is proposed to precisely modulate the closed-pore structure in HC, and the spatial configuration can be tuned by aldehyde molecules side groups with different numbers of benzene rings, resulting in PF with varying crosslinking degrees and backbone stiffness. We demonstrate that resin synthesized from benzaldehyde grafting a moderate number of benzene rings exhibits the internal space (or free volume) because it balances cross-linking degree and backbone stiffness. This synergy suppresses the rearrangement of carbon layers, facilitating the formation of curved and small carbon microcrystals , which in turn leads to a higher generation of closed pores during carbonization. As a result, the benzaldehyde-derived HC demonstrates a high reversible capacity of 324.7 mAh g −1 and a notable plateau capacity of 243.2 mAh g −1 . Overall, this work opens new avenues at the molecular level for the design of closed pores in other polymer-derived HC anodes for energy storage materials.