Enhancing Plateau Capacity of Binder‐Free and Self‐Supported Napkin‐Based Hard Carbon Anodes for Sodium‐Ion Batteries Via a Pre‐Oxidation Modulation Strategy

The practical deployment of hard carbon (HC) anodes in sodium‐ion batteries is fundamentally constrained by inadequate initial Coulombic efficiency (ICE) and limited plateau capacity. These challenges are addressed through precision preoxidation modulation and temperature‐programmed carbonization of biomass‐derived precursors to achieve high‐reversibility sodium storage. The closed/ultramicroporous structure of HC enhances sodium‐ion storage kinetics, and the optimized HC anode exhibits a remarkable reversible capacity of 395 mAh g −1 at 30 mA g −1 , and a higher plateau capacity of 266 mAh g −1 (compared with typically 150–200 mAh g −1 in most reported systems). The anode material demonstrates outstanding rate capability (105.7 mAh g −1 at 1000 mA g −1 ), representing a doubling enhancement compared to materials without closed/ultramicropores structure. Further investigations prove a hybrid sodium storage mechanism, involving surface adsorption, interlayer intercalation, and pore‐filling of sodium ions. This work established a versatile methodology for manipulating carbon nanostructures through rational modulation of oxygen‐functional groups and carbonization temperature, providing new insights for advancing the development of HC with enhanced plateau capacity and exploring flexible anode materials.