From food waste to high-capacity hard carbon for rechargeable sodium-ion batteries

•The study involved the preparation of P-doped hard carbon by utilizing coffee grounds and phosphoric acid.•Phosphorus dopants were found to play a pivotal role in enhancing the electrochemical performance of the hard carbon materials.•The enhancement was attributed to the efficient integration of phosphorus ions into the carbon framework.•The synthesized HCG-1300-2 exhibited an outstanding specific capacity of 341 mAh g−1 with an initial Coulombic efficiency of 83 % when operated at a current density of 20 mA g−1.•The impressive performance was largely due to the optimal integration of phosphorus ions into the carbon structure.