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

In this study, we introduce a straightforward and effective approach to produce P-doped hard carbon using coffee grounds as the precursor, with H₃PO₄ serving as the doping agent. By varying the concentrations of H₃PO₄ (1 M, 2 M, and 3 M), we aimed to determine the optimal doping level for maximizing the incorporation of phosphorus ions into the carbon framework. Our investigation revealed that using 2 M of H₃PO₄ as the dopant material for hard carbon led to promising electrochemical performance when employed as an anode material for sodium-ion batteries. The P-doped hard carbon, carbonized at 1300 °C, exhibited an impressive reversible capacity of 341 mAh g⁻¹ at a current density of 20 mA g⁻¹, with an initial Coulombic efficiency (ICE) of 83 %. This outstanding electrochemical performance of P-doped hard carbon can be attributed to its unique properties, including a porous agglomerated structure, a significant interlayer spacing, and the formation of C–P bonds.