Flexible carbon nanofibers with multichannel and porous structure as freestanding anode for excellent sodium storage

Hard carbon is the most commonly used anode material for sodium-ion batteries (SIBs). However, it has the drawback of having inferior capacity at high rates due to low ion-diffusion kinetics. Rational design of hard carbon with a hierarchical pore structure and multichannel structure can address this issue. Herein, we introduced an electrospinning method for preparing flexible carbon nanofibers as a freestanding anode for SIBs. The pore structure can be modified by adjusting the amount of Pluronic F-127 (F127) added to the spinning solution. This strategy results in the formation of numerous micropores and mesopores, along with pore-derived defects, effectively increasing the number of sites available for sodium storage. The existence of multichannel facilitates the migration of sodium ions. PCNF-1 possesses an appropriate pore structure with the least amount of added pore-forming agent exhibits exceptional electrochemical performance. It delivers a reversible capacity of 286 mA h g-1 at a current density of 50 mA g-1 with an initial Coulombic efficiency (ICE) of 82 %. At 5 A g-1, it delivers a capacity of 211 mAh g-1. Furthermore, it demonstrates a high retention rate of 79 % at 1 A g-1 even after 1000 cycles. Notably, in full-cell tests, PCNF-1, when paired with a Na3V2(PO4)3 cathode, achieved a specific capacity of 253 mA h g-1 in the second cycle and maintained a retention rate of 51 % after 200 cycles at a current density of 1 A g-1.