Synthesis of FeS-impregnated heteroatom-doped carbon nanofibers assisted by one-step vulcanization for superior sodium storage

Highlights: : • FeS/N,S-doped CNFs film is synthesized by electrospinning combined with one-step vulcanization. • The heteroatom-doped CNFs skeleton improves the conductivity and structural stability. • The enhanced pseudocapacitive redox reactions facilitate charge transfer and ion diffusion. • The FeS@CNFs exhibit excellent electrochemical performance. -- Abstract: Severe volume changes during sodiation/desodiation and the sluggish sodium reaction kinetics of FeS limit its applications in high-performance sodium-ion batteries (SIBs). To solve these problems, free-standing FeS nanocrystallites-impregnated porous N, S-doped carbon nanofibers (FeS@CNFs) is fabricated through an electrospinning technique combined with one-step vulcanization. During the vulcanization, the Fe precursor containing as-spun film is carbonized and sulfurated, and the carbon matrix is functionalized by S-containing oxygen groups meanwhile. The obtained free-standing and flexible FeS@CNFs film can be directly used as anode for SIBs without slurry-casting. The film exhibits prominent electrochemical property because low electronic conductivity and aggregation of FeS particles are resolved by introducing well-distributed FeS nanocrystallites into the conductive carbon nanofibers network. In addition, the film exhibits good structural stability with limited volume changes during cycling due to the buffer effects of CNFs. The film shows a high specific capacity of 530 mA h g^-1 at 0.2 Ag^-1 with a high initial Coulombic efficiency of 86.2%. Additionally, with enhanced surface-dominant pseudocapacitive redox reactions, which facilitate charge transfer and ion diffusion, the FeS@CNFs delivers capacities of 367 and 278 mA h g^-1 at 10 and 30 Ag^-1, respectively, maintaining long cycling stability with a high capacity retention rate of 87.6% after 700 cycles at 10 Ag^-1.