Bagasse‐Derived Hard Carbon Anode with a Synergistic Sodium Storage Mechanism Induced by Temperature Gradient for High‐Performance Sodium‐Ion Batteries

ABSTRACT Biomass‐derived hard carbon has wide sources, low cost, and natural hierarchical pore structure and surface functional groups, holding huge potential for sodium‐ion batteries (SIBs). Nevertheless, it still faces the challenges including unclear Na‐storage mechanism and inaccurate match between diverse microstructures and desirable electrochemical performance. Herein, a novel biomass‐derived hard carbon with balanced graphite crystallites and defect sites, appropriate carbon interlayer spacing, and mesopore‐dominated pore characteristics is achieved using bagasse as the precursor though a facile temperature‐gradient carbonization process. Thanks to such unique microstructures, the optimized sample delivers a large initial reversible capacity of 305.5 mAh g −1 , a superior initial coulombic efficiency of 89.8%, and a high capacity retention of 96% after 200 cycles at 100 mA g −1 . Even at 0 °C, it still demonstrates a considerable reversible capacity of 214.2 mAh g −1 after 100 cycles at 100 mA g −1 . Importantly, a synergistic Na‐storage mechanism is systematically elaborated, including “adsorption of surface active sites (defects and oxygen‐containing groups) and local pore‐filling” in the potential slope region (>0.1 V) and “interlayer intercalation and secondary pore‐filling” in the potential plateau region (<0.1 V). This work advances the understanding of bagasse‐derived hard carbon anode and its synergistic Na‐storage mechanism for SIBs.