Boron/phosphorus co-doped nitrogen-rich carbon nanofiber with flexible anode for robust sodium-ion battery

Flexible energy storage devices have been paid much attention and adapts to apply in various fields. Benefiting from the active sites of boron (B) and phosphorus (P) doping materials, co-doped carbon materials are widely used in energy storage devices for the enhanced electrochemical performance. Herein, B and P co-doped flexible carbon nanofibers with nitrogen-rich (B-P/NC) are investigated with electrospinning for sodium-ion battery. The flexible of binderless B-P/NC with annealing of 600 °C (B-P/NC-600) exhibits the remarkable performance for the robust capacity of 200 mAh/g at 0.1 A/g after 500 cycles and a durable reversible capacity of 160 mAh/g even at 1 A/g after 12,000 cycles, exhibiting the equally commendable stability of flexible B-P/NC-600. In addition, B-P/NC-600 delivers the reversible capacity of 265 mAh/g with the test temperature of 60 °C. More importantly, the flexible B-P/NC-600 is fabricated as anode for the whole battery, delivering the capacity of 90 mAh/g at 1 A/g after 200 cycles. Meanwhile, theoretical calculation further verified that boron and phosphorus co-doping can improve the adsorption capacity of nitrogen carbon materials. The favorable performance of flexible B-P/NC-600 can be ascribed to the nitrogen-rich carbon nanofibers with three-dimensional network matrix for the more active site of boron and phosphorus co-doping. Our work paves the way for the improvement of flexible anodes and wide-operating temperature of sodium-ion batteries by doping approach of much heteroatom.