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 (SBET = 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.