Benzoxazine Chemistry‐Directed Closed‐Pore Engineering in Microspheric Hard Carbon toward Ultrafast Sodium Energy Storage

ABSTRACT The enhancement of sodium‐storage plateau capacity through closed‐pore engineering remains a crucial challenge in high‐performance hard carbon anodes. Herein, ạ benzoxazine chemistry‐directed cross‐linking strategy is proposed to synthesize polybenzoxazine‐based polymer spheres (G‐FT) through the polymerization of monomers among natural tea polyphenol, glutamic acid, and formaldehyde. We unveil that the dicarboxylic amine‐structured glutamic acid can simultaneously trigger in‐situ Mannich reaction and esterification with tea polyphenols through a multi‐site linkage mechanism. Such highly cross‐linked and unique Mannich bridge frameworks in the polybenzoxazine‐based precursors facilitate the ordered growth of graphitic microdomains during subsequent carbonization process, resulting in abundant nanoscale closed pores within the derived hard carbon microspheres (G‐FT‐HC). For sodium‐ion storage, G‐FT‐HC delivers a boosted initial Coulombic efficiency (90.6%) and a high capacity (325.7 mAh g ⁻¹ ) along with 68.2% plateau capacity contribution. Meanwhile, the optimized carbon microstructure and inorganic‐rich solid‐electrolyte interphase endow the G‐FT‐HC with superb high‐rate capability (78.9 mAh g ⁻¹ at 15 A g ⁻¹ , ≈16 s to full charge or discharge). Theoretical calculations reveal that in the G‐FT‐HC, nitrogen‐doped pseudo‐graphitic domains together with expanded carbon layers and moderate planar defects favor rapid Na ⁺ diffusion kinetics, while the formed closed‐pore structure promotes Na cluster aggregation, thereby enhancing the Na‐storage at low‐voltage plateau.