Metal-organic frameworks derived FeSe₂@C nanorods interconnected by N-doped graphene nanosheets as advanced anode materials for Na-ion batteries

Herein, unique FeSe₂@C nanorods interconnected by nitrogen-doped graphene nanosheets (FeSe₂@C/NG) were successfully prepared using Fe-based metal-organic framework (MOF) nanorods as sacrificial templates. During the thermal treatment in an inert atmosphere, the FeSe₂ nanoparticles were formed in situ when selenium reacted with Fe species in the MOF. The organic species were simultaneously transformed into a conductive carbon material. After combining with N-doped graphene nanosheets, the obtained FeSe₂@C/NG composites showed an improved reversible capacity, great rate capabilities, and cycling stability as anodes for sodium-ion batteries. The composite electrode comprised a specific capacity of 411 mA h g⁻¹ after 100 cycles at 0.5 A g⁻¹. When tested at a higher current density of 7.0 A g⁻¹, the discharge capacity was 291 mA h g⁻¹. The improved electrochemical properties can be attributed to structural features of composites and the synergistic effect between the components. The one-dimensional nanostructure of FeSe₂@C nanorods can shorten the ion diffusion path. Additionally, the carbon framework derived from the organic species in Fe-MIL-88 and the interconnected N-doped graphene nanosheets imparted a synergistic effect, which led to the formation of a conductive highway that provided a rapid electron transport, an ample ion reaction site, and acted as buffer layers for active materials.