Leveraging <i>Saccharum officinarum</i> for an Exquisite Symmetric Supercapacitor─A Cost-Effective MnCO₃ Synthesis Approach for Energy Storage Application

Sugarcane (<i>Saccharum officinarum</i>) was employed as a sustainable carbon source to synthesize three-dimensional (3D) spherical manganese carbonate (MnCO₃) microspheres, offering a green route to advanced electrode material for high-energy-density symmetric supercapacitors. Although numerous synthesis strategies and material modifications have been explored, a detailed evaluation of environmentally friendly synthesis pathways remains essential. In this study, MnCO₃ microspheres were successfully synthesized via a sugar-derived green synthesis followed by hydrothermal treatment. Owing to their distinctive morphology and tunable structure, MnCO₃ electrodes outperformed several conventional metal oxides and hydroxides. Electrochemical studies in a three-electrode configuration under alkaline conditions demonstrated a specific capacitance of 366 F/g at 0.7 A/g and an excellent cycling stability, with 99% coulombic efficiency after 3000 cycles. Upon configuration into a symmetric supercapacitor device, the electrode operated at a high voltage of 1.2 V, delivering a specific capacitance of 179.8 F/g at 0.5 mA while retaining 50 F/g at 3 mA. The device exhibited an outstanding durability with 99.6% coulombic efficiency over 10 000 cycles and achieved a high energy density of 35.9 Wh/kg and a power density of 2590.6 W/kg. These findings highlight the potential of sugar-cane-derived 3D MnCO₃ microspheres as cost-effective, ecofriendly electrode materials for next-generation sustainable energy storage systems.