From Natural Fibers to High-Performance Anodes: Sisal Hemp Derived Hard Carbon for Na-/K-Ion Batteries and Mechanism Exploration.

Hard carbon (HC) is a promising anode material in alkali metal ion batteries owing to its cost-effectiveness, abundant sources, and low working voltage. However, challenges persist in achiving prolonged cycling stability and consistent capacity, and the sodium storage mechanism in HC is still debated. Herein, an unreported biomass precursor, "sisal," for deriving hard carbon is developed. A series of sisal hemp-derived hard carbon with natural 3D porous channels are prepared. Through phase characterization and electrochemical testing, the relationship between microstructure and sodium storage capacity is elucidated, further confirming the suitability of the "adsorption-insertion-filling" mechanism for sodium storage properties in hard carbon materials. Without the need for any additional modification strategies, this biomass-derived hard carbon demonstrates excellent electrochemical performance in both sodium-ion and potassium-ion batteries (SIBs and PIBs). The as-prepared HC-1300 demonstrates excellent ion storage capability, delivering a high reversible capacity of 345.2 mAh g^-1 in SIBs and 310 mAh g^-1 in PIBs at 0.1 C. Moreover, it maintains a specific capacity of 237.3 mAh g^-1 over 1200 cycles at 1 C when used in SIBs. The excellent cycling stability and superior rate performance are also presented in full cells, highlighting its potential for practical applications.