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. [ABSTRACT FROM AUTHOR]