Intermolecular Hydrogen Bonding Mediated Micropore Activation and Structure Disorder in Hard Carbon for High-Capacity Sodium Storage.

Abstract

Hard carbon (HC) has emerged as a promising anode material for sodium-ion batteries (SIBs); however, the rational design and regulation of its microstructures remain highly challenging. Herein, molecular-level integration between polymerized citric acid-oxamide and sucrose enables micropore manipulation and carbon-layer curvature regulation during carbonization for high-capacity HCs. Intermolecular hydrogen bonding between C═O groups in the polymerized citric acid-oxamide and -OH groups in sucrose alters the local electron density and elongates the C-OH bonds. This promotes preferential pyrolysis of the hybrid precursor below 300 °C without caramelization and favors the formation of blocked micropores. The residual C═O groups decompose at ≥1200 °C, releasing CO₂ that relieves internal stress in carbon layers, thereby generating localized curvature and reopening the initially blocked micropores. The resultant HC is demonstrated to deliver a high capacity of 421.5 mAh g^-1 and enable pouch cells with a layered transition-metal oxide cathode to attain an energy density of 151.8 Wh kg^-1 with excellent cycling stability of 95.4% capacity retention after 800 cycles. This work highlights the critical role of intermolecular bonds for microstructure reconfiguration in Na storage of HC.