Scotch Pine Cones-Derived Hard Carbon as an Anode Material for Sodium-Ion Battery Applications

A biobased anode material for sodium-ion batteries (SIBs) was prepared through the simple pyrolysis of Scotch pine cones (Pinus sylvestris, SPC), followed by a heteroatom doping modification. The resulting nitrogen-doped hard carbon exhibited a high reversible capacity of 273 mA·h·g^–1 at a current density of 25 mA·g^–1 compared to the undoped material (197 mA·h·g^–1). X-ray diffraction analysis shows that the produced hard carbon from the biomass is highly amorphous in nature, and high-resolution transmission electron microscopy images reveal the presence of localized graphite-like structures that are found to be beneficial for the storage and transport of Na⁺ ions during charging/discharging. Experimental results demonstrated that the increased specific surface area (S_BET = 424 m²·g^–1), high micropore volume (0.177 cm³·g^–1), and expanded interlayer spacing (>3.7 Å) and a high Na⁺-ion diffusion coefficient (3.08 × 10^–16 cm²·s^–1) facilitated the diffusion of sodium ions, leading to a high capacity retention of 80% after 250 cycles for the SPC-N material over the undoped one, SPC (71%). This study highlights the potential of low-cost, widely available biobased Scotch pine cones as an alternative anode material to enhance the sustainability of SIB production.