Defects and Oxygen Functional Groups Modulated Soft Carbon with Abundant Closed Pores and Robust Interface for High-Performance Na+-Ion Batteries

Soft carbons with inherently high graphitization degree typically suffer from limited specific capacity and low initial Coulombic efficiency (ICE) for Na⁺-ion batteries (NIBs), hindering their development and practical application. Herein, defect and oxygen functional group engineering strategy by incorporating resin-derived hard carbon and cost-effective iron-based substances is proposed enables the design of a unique layered soft carbon with enhanced efficiency and stable interfaces with the electrolytes. The increased C═O functional groups and Fe─O─C bond contributed by Fe-based species significantly improve reversible Na⁺- adsorption in the inclined region and enhance the structural stability of the electrode. Additionally, phenolic resin-derived carbon increases the micropores and thus reduces the graphitization degree. The increased closed pores induced by the reconstruction of the carbon structure at high temperature enhance the Na⁺-storage ability. Consequently, the material achieves a high Na⁺-storage capacity of 311.0 mAh g⁻¹ with an improved ICE of 93.89% at 0.1 A g⁻¹. Even cycled at 1 A g⁻¹, it can deliver a high capacity of 269.3 mAh g⁻¹ with excellent stability over 800 cycles, outperforming previously reported soft carbon anodes. This innovative strategy provides a practical and cost-effective pathway for designing advanced carbon anodes for NIBs.