Nitrogen and fluorine co-doped graphene as a high-performance anode material for lithium-ion batteries

Abstract

Nitrogen and fluorine co-doped graphene (NFG) with the N and F content as high as 3.24 and 10.9 at% respectively was prepared through the hydrothermal reaction of trimethylamine tri(hydrofluoride) [(C₂H₅)₃N·3HF] and aqueous-dispersed graphene oxide (GO) as the anode material for lithium ion batteries (LIBs). The N and F co-doping in graphene increased the disorder and defects of the framework, enlarged the space of the interlayer, wrinkled the nanosheets with many open-edge sites, and thus facilitated Li ion diffusion through the electrode compared with sole-N or F doped graphene. X-ray photoelectron spectroscopy (XPS) analysis of NFG demonstrated the presence of active pyridine and pyrrolic type N, and highly electrically conductive graphitic N and the semi-ionic C–F bond in the structure. The N and F doping content and the component types of N and F functional groups could be controlled by the hydrothermal temperature. The NFG prepared at 150 °C exhibited the best electrochemical performances when tested as the anode for LIBs, including the high coulombic efficiency in the first cycle (56.7%), superior reversible specific discharge capacity (1075 mA h g⁻¹ at 100 mA g⁻¹), excellent rate capabilities (305 mA h g⁻¹ at 5 A g⁻¹), and outstanding cycling stability (capacity retention of ∼95% at 5 A g⁻¹ after 2000 cycles), which demonstrated that NFG was a promising candidate for anode materials of high-rate LIBs.