Microstructure-Interface Modulation Boosts Sodium Storage Capacity and Stability of Hard Carbon.

The development of hard carbon (HC) anode is severely hindered by limited Na⁺ storage capacity and poor cycling stability, which are closely related to its microstructure and interface. In this work, a synergistic microstructure-interface modulation strategy is demonstrated to regulate the Na⁺ storage active sites and structural stability of resin-based HC. The introduced C═O enables reversible Na⁺ adsorption, while carboxyl and neighboring phenolic hydroxyl functional groups anchor the template metal ions (Zn²⁺), thereby constructing a hierarchical pore structure with abundant sites for reversible Na⁺ storage. Additionally, expanded interlayer spacing promotes the kinetics of reversible Na⁺ intercalation/deintercalation. Based on this strategy, the optimized HC material (ZGB-HC) exhibits an extra-high capacity of 406 mAh g⁻¹ at 50 mA g⁻¹ and maintains exceptional cycling stability of over 1000 cycles for 1 A g⁻¹. More surprisingly, the assembled Na₃V₂(PO₄)₃||ZGB-HC full cell delivers a superior rate capability of 96.4 mAh g⁻¹ at 4 C and maintains excellent cycling stability for over 250 cycles at 2C. This work develops an innovative strategy for designing HC anodes with advanced microstructure-interface and new insights into their structural evolution during cycling.