Hierarchically porous aramid-derived hard carbon with high-rate capability as anodes for sodium-ion batteries

The morphology and structure of hard carbon (HC) as anodes are pivotal for enhancing the rate capability of sodium-ion batteries (SIBs). Aramid fiber-derived HC, for the first time, is employed as an anode material of SIBs through a two-step treatment strategy involving nanofibrillation in solution of DMSO/KOH (dimethyl sulfoxide/potassium hydroxide) followed by freeze-drying. Compared to the control sample that is prepared by direct carbonization, the average fiber diameter is significantly reduced from about 10 μm to 20 nm, and a hierarchically porous structure with a higher specific surface area and a larger pore volume is formed. Its typical structure can enhance Na⁺ diffusion kinetics and improve electrical conductivity of HC, as evidenced by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements. The carbonization temperature is varied and the sodium storage mechanism is also investigated. The optimized HC exhibits a better rate capability of 136.7 mAh g⁻¹ at 20C and a higher initial Coulombic efficiency (ICE) of 82.3 % compared to the control sample. This work not only presents a HC anode design with high rate capability but also highlights the potential of aramid fibers as precursors of energy storage.