Inhibiting the cyclization of PAN by carboxyl groups for carbon nanofibers with balanced Na+ storage performance and ICE

• The cyclization of stabilization process for polyacrylonitrile is limited and realizing a disordered carbon structure. • The formation of sodium carboxylate can lead to hard carbon with abundant internal pores. • Enhance the understanding of Na + storage “adsorption-insertion-pore filling” mechanism in polyacrylonitrile-derived hard carbon. Hard carbon nanofiber derived from electrospinning polyacrylonitrile (PAN) is regarded as the promising electrode featuring the low-cost and simple preparation advantages, while it possesses the low plateau capacity, limiting its application as anode for the sodium ion (Na + ) storage technologies. The main obstacle is that the cyclization of PAN during stabilization leads to the formation of ordered carbon structures. Herein, nanofibers anodes with disordered structures and abundant internal nanopores are fabricated by using carboxyl-functionalized PAN. The cyan (–CN) of PAN turns to sodium carboxylate (–COONa) during the hydrolysis process in NaOH solution, so that the cyclization in stabilization process is limited and realizing disordered carbon structures. Meanwhile, the formation of –COONa can lead to hard carbon with abundant internal pores, thereby resulting in an extended plateau region during discharging. The optimized PCNFs2-700-1400 anode delivers a satisfactory reversible capacity of 286 mAh/g at 0.02 A/g with an initial coulombic efficiency (ICE) of 73%. The larger plateau capacity of 183 mAh/g is ascribed to the filling of Na + in the internal pores and insertion in the pseudo-graphitic. This strategy is expected to help enhance the understanding of Na + storage “adsorption-insertion-pore filling” mechanism in PAN-derived hard carbon.