Open sesame: tailoring the microstructure of biomass-derived hard carbon for high-efficiency sodium-ion battery anodes

The increasing reliance on intermittent renewable energy sources underscores the need for efficient large-scale energy storage systems with enhanced electrochemical performance. This work addresses the critical challenge of developing high-performance sodium-ion battery (SIB) anodes by proposing a universal strategy to optimize biomass-derived hard carbon (HC) materials. Using sesame shells as a precursor, an esterification-crosslinking method involving acid pretreatment and L-aspartic acid modification was employed to tailor the microstructure and functional group composition of HC. The resulting material exhibits a reversible capacity of 351 mAh g⁻¹, an initial Coulombic efficiency of 86.6 %, and exceptional rate capability (233 mAh g⁻¹ at 600 mA g⁻¹), alongside 96.5 % capacity retention at 300 mA g⁻¹ after 500 cycles. Structural and computational analyses reveal that the enhanced performance arises from C[dbnd]O defects promoting Na⁺ adsorption, reduced open porosity, and a disordered carbon framework facilitating an adsorption-intercalation/filling storage mechanism. The strategy's effectiveness is further validated across diverse biomass precursors, including almond shells, soybean hulls, and corncobs, demonstrating its versatility. This approach provides a scalable pathway to advance electrode material design for next-generation energy storage technologies, with implications for improving the practicality and performance metrics of SIBs in grid-scale applications.