Carbon‐Layer Curvature Regulates Sodium Storage via Interfacial Electric Field Engineering

ABSTRACT Understanding how carbon‐layer curvature regulates sodium storage in hard carbon remains challenging because the missing link between structural curvature and Na + transport kinetics has not been experimentally resolved. Herein, hard carbons with tunable curvature are developed to elucidate the role of interfacial electrostatics in sodium storage. Kelvin probe force microscopy directly reveals a positive correlation between curvature and surface potential, providing experimental evidence that curvature governs the local electrostatic environment. Operando structural analyses demonstrate that enhanced interfacial electric fields promote early Na + intercalation, whereas excessively strong fields hinder Na + migration toward low‐potential pore filling. Consequently, Na + transport exhibits a non‐monotonic dependence on interfacial electrostatics, where moderate curvature simultaneously enables rapid Na + capture and efficient bulk transport. The optimized BC‐1000 sample, with balanced curvature and interfacial electric field, delivers a high reversible capacity of 207.5 mAh g − 1 at 10 A g − 1 . This work establishes interfacial electrostatics as the missing link connecting carbon‐layer curvature and sodium‐storage kinetics, providing a new design principle for high‐performance hard carbon anodes.