Liquid-Phase Oxidation Engineering of Pine Wood Powder-Derived Hard Carbon for Low-Cost Sodium-Ion Batteries

High performance, low cost, and sustainability are the core competitive advantages of hard carbon for sodium-ion batteries (SIBs). The improper disposal of large volumes of biomass waste exacerbates environmental burdens, making the transformation of such waste into carbon-based materials for sustainable energy storage particularly significant. In this work, we reported the synthesis of hard carbons derived from waste pine wood powder (PP), with enhanced sodium storage performance achieved via a liquid-phase HNO₃ preoxidation strategy. The introduction of abundant oxygen groups during preoxidation promotes structural cross-linking and facilitates carbon framework rearrangement during carbonization, resulting in a disordered structure with reduced defect density, lower specific surface area, fewer open pores, and more enlarged closed pores. Finally, the optimized OPP-1200 delivers a much higher reversible capacity (227.1 mAh g^-1 at 20 mA g^-1) and initial Coulombic efficiency (66.1%) compared to that of the unmodified PP-1200 (116.0 mAh g^-1 and 42.5%, respectively). Furthermore, OPP-1200 exhibits superior cycling stability relative to PP-1200. This study offers an effective and scalable strategy for converting waste biomass into low-cost and high-value hard carbon anodes for SIBs, offering new insights into sustainable energy material development.