Nitrogen-Doped Hard Carbon on Nickel Foam as Free-Standing Anodes for High-Performance Sodium-Ion Batteries

Nitrogen-doped hard carbon on Ni foam (NC/NF) with numerous active sites, expanded interlayer distance (0.49 nm), and highly ordered pseudo-graphic structure is synthesized by a melamine-assisted hydrothermal pretreatment and subsequent pyrolysis procedure. The high content configurations of pyrrolic-nitrogen and pyridinic-nitrogen in NC/NF could provide abundant active sites and defects for efficient Na+ adsorption/desorption and improved transport kinetics. The obvious flocculent structures on carbon surface, corresponding to the highly ordered pseudo-graphic structure, could enhance the transport kinetics for electrons. The strong electrostatic repulsion of pyrrolic-nitrogen could expand interlayer distance, facilitating Na+ insertion/extraction process. The balance between high nitrogen content and sufficient graphitization degree comes into strong carbon frameworks with enhanced structural stability and electronic conductivity. When served as free-standing anodes for sodium-ion batteries (SIBs), NC/NF presents high rate capability of 128.5 mAh g(-1) at 10 A g(-1), and excellent cycling stability of 225.4 mAh g(-1) after 1000 cycles under high current density of 5 A g(-1). These results demonstrate a new light to prepare advanced anodes for SIBs.