A new N/O Co-doped soft-hard carbon nanofibers composite for advanced sodium storage

Carbon-based materials have excellent conductivity, low cost, and environmental friendliness, making them the primary choice for negative electrode in sodium ion batteries (SIBs). Among them, hard-carbon and soft-carbon as amorphous carbon are considered to have potential as negative electrode for SIBs. However, soft-carbon exhibits a slow charging speed and poor low-temperature performance and hard-carbon behaves a low initial coulombic efficiency, resulting in a key obstacle to their extensive applications in SIBs. Herein, a new N/O co-doping soft-hard carbon nanofiber (PCNF) composite was prepared by electrospinning with heat treatment method, petroleum coke (PC) as soft-carbon and oxygen source and polyacrylonitrile (PAN) as hard-carbon and nitrogen source. The optimal PCNF-800 carbonization at 800 °C delivers an enhancement capacity of 296.1 mAh g −1 at 25 mA g −1 after 100 cycles with the capacity retention of 88.2 %. The excellent electrochemical property is ascribed to the co-doping of N/O in the carbon resulting in the large number of defects which could enhance Na + adsorption and transport, the appropriate interlayer spacing, the porous nanofiber mircostructure, and the synergistic effect between soft and hard carbon. Meanwhile, this study provides a possible new idea for the high-value utilization of petroleum coke.