Electrospun Perforated Carbon Spheres with an Ultramicropore-Rich Architecture for Sodium-Ion Storage

Hard carbon (HC) is a promising anode material for sodium-ion batteries (SIBs) because its disordered structure and relatively large interlayer spacing facilitate reversible Na+ storage. Polyacrylonitrile (PAN) is an attractive carbon precursor with high carbon yield and in situ nitrogen doping. However, conventional PAN-derived HC often suffers from sluggish ion transport and limited reversible capacity. Herein, electrospun perforated carbon spheres (PCS) with an ultramicropore-rich architecture were fabricated via coaxial electrospinning, sacrificial templating, and high-temperature carbonization. The optimized PCS exhibits a CO2-derived apparent specific surface area of 362.5 m2 g-1 and deliver a reversible capacity of 312.9 mAh g-1 at 20 mA g-1, including a plateau capacity of 180.2 mAh g-1. It also delivers a rate capability of 145.6 mAh g-1 at 2 A g-1 and retains 88.0% of its capacity after 400 cycles at 50 mA g-1. Ex situ XRD, in situ Raman spectroscopy and electrochemical analyses are consistent with an adsorption-intercalation/pore-filling sodium-storage mechanism. A full cell paired with a Na4Fe3(PO4)2P2O7 (NFPP) cathode delivers an energy density of 209 Wh kg-1 based on the total mass of active materials. These results demonstrate that electrospun carbon spheres with tailored pore structures are promising anodes for advanced SIBs.