Engineering Molecular Rivets to Tune Pore Structure for Significantly Enhanced Sodium Storage

The large-scale application of hard carbon (HC) has been hindered due to its low specific capacity, poor cycling stability, and the lack of a simple preparation process. This study utilized 5-hydroxymethylfurfural (HMF) generated from hydrolysis as a crosslinking bridge to construct a crosslinking precursor via intermolecular reaction, thereby synthesizing hard carbon (HC) rich in closed pores and enhancing its reversible capacity. Moreover, the intermolecular cross-linking strategy results in the HC rich in C═O functional groups, which facilitates the binding of PF₆ ⁻ anions and promotes the formation of a stable inorganic-rich solid electrolyte interphase (SEI), significantly enhancing Na⁺ transport kinetics. The optimized HC increases the closed pore volume to 0.0447 cm³ g⁻¹. And delivers a high reversible specific capacity of 329.19 mAh g⁻¹, with a plateau capacity of 233.8 mAh g⁻¹. Even under a high current rate of 5C, the material maintains a reversible capacity of 187.33 mAh g⁻¹. Moreover, it exhibits excellent cycling stability, retaining a specific capacity of 243.85 mAh g⁻¹ after 1000 cycles at 1C. This work provides a new strategy for designing HC with high capacity and long cycling life.