Unveiling the Critical Role of Pre‐Hydrothermal Effect in Plant Biowaste‐Derived Hard Carbon for Superior Rate Capability and Cycle Life in Sodium‐Ion Batteries

Abstract Leveraging economically viable plant bio‐waste‐derived hard carbon (HC) anode materials for sodium‐ion batteries is logical. Many plants' bio‐waste materials are used as HC precursors, but their fabrication process is usually limited by direct carbonization which constrains their large‐scale sustainability. Herein, the critical role of the pre‐hydrothermal carbonization effect in regulating the structure and interfacial Na + storage mechanism/performance of HC derived from oak leaves (OL) biowaste (OLHC) is reported. The resultant OLHC demonstrates a high‐reversible capacity (378 mAh g −1 at 0.1 C), superior rate performance (272.9 mAh g −1 at 10 C), remarkable cycling performance (75% after 8000 cycles at 10 C), and adequate ICE (85%). Advanced ex/in situ characterization combined with theoretical calculations reveals that hydrothermal pre‐regulation of OLHC stabilizes the spherical particles, introducing more active sites and promoting surface properties with oxygen dopant‐induced defects, which shows uneven surface electrostatic potential and lower activation energy for Na + adsorption thus generates a thin layer of PF 6 − /NaF‐enriched core‐shell‐like SEI modulation with organic–inorganic composition. This enables fast interfacial Na + diffusion kinetics, contributing to high‐capacity retention and stable cycling performance. The studies offer a systematic understanding of the pre‐hydrothermal strategy for the structural design of HC from plant‐leaves‐biowaste with true sustainability and improved performance for SIBs.