<p>Hard carbon is considered one of the most promising anode materials for sodium-ion batteries. Biomass-derived carbon precursors are especially appealing owing to their renewability, natural abundance, and low cost. Herein, low-ash walnut shell is employed as a precursor to prepare hard carbon, and a melamine-assisted nitrogen-doping strategy is developed to tailor its microstructure and sodium-storage behavior. The resulting nitrogen-doped hard carbon exhibits a robust carbon framework with enlarged interlayer spacing. Moreover, pyridinic N and pyrrolic N are the predominant nitrogen configurations, contributing 52.8% and 35.3% of the total nitrogen content, respectively. These nitrogen species enhance the sodium adsorption affinity, introduce abundant defect sites, and create additional electrochemically active sites for sodium storage. Benefiting from these structural features, the optimized sample HN20 delivers an initial reversible capacity of 287.4 mAh&#xa0;g⁻¹ with a high initial Coulombic efficiency of 89.4% at 30&#xa0;mA&#xa0;g⁻¹, together with a reversible capacity of 222.2&#xa0;mAh&#xa0;g⁻¹ at 60&#xa0;mA&#xa0;g⁻¹. The improved electrochemical performance is ascribed to the synergistic effects of increased specific surface area, widened interlayer spacing, and abundant redox-active sites. This work highlights melamine-assisted nitrogen doping as an effective approach for constructing high-performance biomass-derived hard carbon anodes for sodium-ion batteries.</p> Graphical abstract <p></p>