Facile fabrication of bamboo-derived hard carbon as anode for sodium-ion battery: Roles of acid-leaching and pre‑carbonization treatments

Bamboo-derived hard carbon emerges as a sustainable anode candidate for sodium-ion batteries, yet its electrochemical performance is hindered by inherent impurities and disordered microstructures. This study explores the synergistic effects of acid-leaching and pre‑carbonization, prior to high-temperature carbonization at 1300 °C, on enhancing sodium storage performance. Acid-leaching at 80 °C with a solid-liquid ratio of 1:15 for 30 min using 6 wt% HCl selectively removes hemicellulose and ash while reducing oxygen-containing groups, leading to an increase in edge defects and the retention of C O functional groups. These two active sites act as pseudocapacitive centers, enhancing capacity in the sloping region. Pre‑carbonization at 500 °C generates interconnected mesopores (0.038 cm 3  g −1 ), facilitating sodium-ion insertion in the plateau region. Additionally, the high carbon to oxygen ratio from acid-leaching, together with the enhanced graphite stacking (L c  = 1.202 nm) induced by pre‑carbonization, improves the electrical conductivity and ion diffusion capability of the hard carbon. Compared with hard carbons derived from AcOH-leached, water-treated, and raw feedstocks, the HCl-leached hard carbon anode exhibits a higher initial Coulombic efficiency (70.4 %), enhanced rate capability (201.4 mAh g −1 at 5C), and a 32 % reduction in charge-transfer resistance. These findings highlight the role of structural engineering in enhancing renewable energy storage, directly linking microstructural modifications to electrochemical performance for sustainable design of high-performance biomass-derived sodium-ion battery anodes.