Hydrothermally Carbonized Corncob‐Derived Hard Carbon Anodes for High‐Performance Sodium‐Ion Batteries

The selection of an effective anode material is a core component in the development of sodium-ion batteries (NIBs) as an achievable alternative to lithium-ion batteries. The foremost considerations include cost-effectiveness, availability, sustainability, and the physicochemical properties required for sodium-ion storage. Biomass-derived hard carbon is among the most promising anode materials due to its favorable structural characteristics, high sodium storage capacity, and low cost of raw material sourcing. However, the main limitations of hard carbon anodes remain restricted by their low initial Coulombic efficiency (ICE) and specific capacity. Herein, corncob-derived hard carbon anodes are synthesized using a two-step process involving hydrothermal carbonization and high-temperature annealing at 1000, 1250, and 1500 °C. The structural and electrochemical properties of the resulting materials are systematically investigated using multiple characterization techniques. Electrochemical characterization demonstrates that the hard carbon annealed at 1500 °C exhibits the highest reversible capacity of 319 mAh g−1 at a C/20 rate, along with an ICE of 89%, attributed to optimized porosity, improved structural order and reduced defect density. These findings highlight the potential of corncob-derived hard carbon as a sustainable and efficient anode material for next-generation NIBs.