Nitrogen/fluorine dual-doped resin-based hard carbon anode with high capacity retention for lithium storage

Heteroatom doping of carbon materials can effectively alter the microstructure and conductivity, thereby improving the electrochemical performance of lithium-ion batteries (LIBs) hard carbon anodes. Herein, a resin-based hard carbon material (NFHC-1200) with co-doped N and F was prepared by one-step pyrolysis method using phenolic resin as the carbon source and ammonium fluoride as the doped N and F sources. Benefiting from the synergistic effects of co-doping, NFHC-1200 exhibited a wider interlayer distance (0.385 nm), a larger specific surface area (93.31 m² g⁻¹), and a greater number of Li⁺ storage active sites (I_D/I_G = 1.754) when compared to undoped HC-1200 and single-atom doped NHC-1200 hard carbon materials. The results of electrochemical performance demonstrated that the electrochemical properties of NFHC-1200 was significantly improved for co-doped N and F. It exhibited an initial discharge capacity of 614.6 mAh g⁻¹ at 37.2 mA g⁻¹, a reversible capacity of 365.2 mAh g⁻¹ with a capacity retention rate of 97.66% even after 150 cycles, and a rate performance of 131 mAh g⁻¹ even at a high current density of 5C (1C = 372 mAh g⁻¹), which were much higher than those observed from NHC-1200 and HC-1200 under the same test conditions. Overall, this work clearly clarifies the mechanism of N/F co-doping synergistic effects to enhance the electrochemical properties of hard carbon materials by comparing the differences in microstructure and electrochemical properties of NFHC-1200 with NHC-1200 and HC-1200, which may provide a new insight into the modification of hard carbon materials.