Optimizing Hard Carbon Anodes from Agricultural Biomass for Superior Lithium and Sodium Ion Battery Performance

Biomass‐derived carbon materials are gaining attention for their environmental and economic advantages in waste resource recovery, particularly for their potential as high‐energy materials for alkali metal ion storage. However, ensuring the reliability of secondary battery anodes remains a significant hurdle. Here, we report Areca Catechu sheath‐inner part derived carbon (referred to as ASIC) as a high‐performance anode for both rechargeable Li‐ion (LIBs) and Na‐ion batteries (SIBs). We explore the microstructure and electrochemical performance of ASIC materials synthesized at various pyrolysis temperatures ranging from 700 to 1400 °C. ASIC‐9, pyrolyzed at 900 °C, exhibits multilayer stacked sheets with the highest specific surface area, and the least lateral size and stacking height. ASIC‐14, pyrolyzed at 1400 °C, demonstrates the most ordered carbon structure with the least defect concentration and the highest stacking height and an increased lateral size. ASIC‐9 achieves the highest capacities (676 mAh/g at 0.134 C) and rate performance (94 mAh/g at 13.4 C) for hosting Li+ ions, while ASIC‐14 exhibits superior electrochemical performance for hosting Na+ ions, maintaining a high specific capacity after 300 cycles with over 99.5 % Coulombic efficiency. This comprehensive understanding of structure‐property relationships paves the way for the practical utilization of biomass‐derived carbon in various battery applications.