Structural properties and electrochemical measurement performances of hard carbon obtained from banana peel

In recent years, the development of cost-effective and sustainable materials has become increasingly important. In this study, hard carbon produced from banana peel biomass waste was synthesized at 1200 °C, with a heating rate of 3 °C min⁻¹, under an Ar atmosphere for 1 h. Characterization results confirmed the amorphous nature of the obtained hard carbon, as evidenced by two broad peaks in the XRD pattern. Raman spectroscopy indicated a relatively high defect density in the banana-peel-derived hard carbon. The material exhibited a high $$I_D/I_G$$ ratio, suggesting the presence of abundant electrochemically active defect sites. Sodium-ion storage behavior was further supported by BET, SEM, and N₂ adsorption isotherm analyses. Electrochemical tests showed that the initial discharge capacity exceeded 126.86 mAh g⁻¹, while the capacity remained approximately 98.06 mAh g⁻¹ at the 45th cycle. Sharp redox couples in the CV curves around ~0.1–0.01 V support a pore-filling/plateau-type sodium storage mechanism, while the sloping profiles in the 0.1–3.0 V region indicate the contribution of surface-driven capacitive processes. C-rate tests confirmed the expected capacity decay with increasing current density and partial recovery when returning to a lower C-rate. These findings demonstrate that banana peel waste can be converted into environmentally friendly hard carbon anodes with competitive capacity, good cyclability, and potentially low cost for sodium-ion batteries (SIBs). This approach is promising for circular-economy-oriented and large-scale energy storage applications.