Free-standing and binder-free sodium-ion electrodes with ultralong cycle life and high rate performance based on porous carbon nanofibers

Free-standing and binder-free porous carbon nanofibers (P-CNFs) electrodes were prepared by pyrolysis of PAN-F127/DMF nanofibers via an electrospinning process as potential anodes for Na-ion batteries (NIB). The P-CNFs delivers a reversible capacity of 266 mA h g^-1 after 100 cycles at 0.2 C, corresponding to ∼80% of the initial charge capacity. When cycled at a current density as high as 500 mA g^-1 (2 C), it still delivers a reversible capacity of ∼140 mA h g^-1 after 1000 cycles. The improvement of electrochemical performance is attributed to the special design and microstructure of P-CNFs, which conferred a variety of advantages: hierarchical porous channels enabling short transport length for ions and electrons, 3D interconnected structure resulting in low contact resistances, good mechanical properties leading to the excellent morphology stability.