• Addition of sodium carbonate during carbonization at 1100 °C modulates the open pore structure of wood-derived hard carbon, increasing interlayer spacing and creating uniform 2–3 nm pores.
• The optimized hard carbon anode delivers a high reversible capacity of 326 mAh g−1 at 30 mA g−1 and excellent rate performance (270 mAh g−1 at 1 A g−1, 68 mAh g−1 at 10 A g−1).
• The anode exhibits good cycling stability, retaining 76.7% capacity after 300 cycles at 1.0 A g−1.
• In situ Raman and GITT analyses reveal an adsorption-intercalation-filling sodium storage mechanism, highlighting the role of open pores in enhancing ion transport and slope capacity.