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

Abstract

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.