Biomass-derived hard carbon, with its advantages of abundant raw material sources, low cost, and environmental friendliness, has become the research hotspot of anodes for sodium-ion batteries. However, the inherent drawbacks of conventional biomass-derived hard carbon, such as narrow interlayer spacing, sluggish Na⁺ diffusion kinetics, excessive specific surface area, and unsatisfactory structural stability, severely restrict its reversible capacity, cycle life, and high-rate capability, hindering its large-scale commercialization. In this study, macadamia nutshell was used as the biomass precursor to prepare cobalt-doped hard carbon anode materials (Co-HC). Systematic characterizations including transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption-desorption measurement, and X-ray photoelectron spectroscopy (XPS) verify that the cobalt doping effectively enlarges the interlayer spacing from 0.371 nm to 0.389 nm, and significantly reduces the specific surface area from 182.805 m²•g⁻¹ to 6.984 m²•g⁻¹ by adjusting the doping concentration and synthesizing process. Cobalt doping not only increases the interlayer spacing, promoting graphitization, enhancing ion diffusion kinetics and electronic conductivity; it also promotes the pore structure transforms from micropore-dominated to mesopore-dominated, substantially reducing the specific surface area. This facilitates rapid Na⁺ diffusion and markedly improves the material's rate performance. Moreover, the expanded graphitic structure of Co-HC effectively enhances the electron conductivity, and the amorphous carbon surrounding the graphitic layers and the oxygen-containing defects provide abundant active sites for Na⁺ adsorption. Electrochemical testing indicates the Co-HC electrode shows a relatively stable capacity of 322.4 mAh•g⁻¹ after 120 cycles at a current density of 30 mA•g⁻¹. Even under a high current density of 300 mA•g⁻¹, it maintains a reversible capacity of 251.1 mAh•g⁻¹ after 900 cycles. The rate performance demonstrates that even at an exceptionally high current of 2000 mA•g⁻¹, the capacity reaches 224.46 mAh•g⁻¹ with a capacity retention of 65.8%. When the current density is reduced to 20 mA•g⁻¹, the Co-HC electrode recovers its capacity to 320.2 mAh•g⁻¹, fully demonstrating its outstanding cycle lifespan and high-rate performance.

Key words: sodium-ion battery, anode, biomass-derived hard carbon, cobalt-doping, structural modification