Abstract: Hard carbon is a promising anode material for sodium-ion batteries due to its low cost, wide source, and long lifespan. However, its lower initial Coulombic efficiency (ICE) and poor capacity limit its practical applications. At present, heteroatom doping is an effective strategy to modulate the amorphous carbon microcrystalline structure and improve the sodium storage performance of carbon materials. The synergistic effect generated by combined heteroatom doping is more conducive to enhancing the electrochemical reactivity of carbon materials than single heteroatom doping. In this study, carbon spheres were synthesized by hydrothermal reaction, with waste residue extracted from potato starch processing waste liquid serving as precursor, based on which boron and nitrogen co-doped biomass carbon spheres were prepared by ball milling and pyrolysis using urea and sodium tetraborate as doping sources. Subsequently, the effects of B and N co-doping on the microstructure and sodium storage properties of carbon materials was investigated. The results indicated that B and N co-doping increased the disorder and enlarged the layer spacing of carbon materials, while forming suitable C=O bonds that were conducive to stable solid electrolyte film (SEI) generation. The as-prepared electrode shows a reversible capacity of 284.3 mAh·g^-1 at a current density of 50 mA·g^-1 with an ICE of 77.0%. After 500 cycles at 2 A·g^-1, its capacity decayed to 122.5 mAh·g^-1 ,with 56.1% capacity retention.

Key words: sodium-ion battery, anode material, potato residue, carbon nanosphere, boron and nitrogen co-doping