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

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.