• • The nitric acid treatment yields a hard carbon with an initial Coulombic efficiency (ICE) of 91.69%, a critical threshold for commercial viability, as it directly impacts the usable capacity and cycle life of full cells.
• • The material retains 83.9% of its capacity at a high current density of 600 mA g−1, demonstrating superior rate capability essential for fast-charging applications and high-power energy storage systems.
• • A full sodium-ion battery cell employing this hard carbon anode and a Na3V2(PO4)3 cathode achieves an energy density of 213.14 Wh kg−1, surpassing many reported biomass-derived hard carbon full cells and approaching the performance of lithium-ion batteries.
• • The synthesis method is facile and scalable, involving a one-step carbonization after nitric acid treatment, which addresses the manufacturing cost barrier that has hindered the commercialization of high-performance hard carbon anodes.