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Binary transition metal selenides have been more promising than single transition metal selenides as anode materials for sodium-ion batteries (SIBs). However, the controlled synthesis of transition metal selenides, especially those derived from metal-organic-frameworks with wellcontrolled structure and morphology is still challenging. In this paper, highly porous NiCoSe 4 @NC composite microspheres were synthesized by simultaneous carbonization and selenization of a NiÀ Co-based metal-organic framework (NiCo-MOF) and characterized by scanning electron microscopy, transition electron microscopy, X-Ray diffraction, X-Ray photoelectron spectroscopy and electrochemical techniques. The rationally engineered NiCoSe 4 @NC composite exhibits a capacity of 325 mAh g À 1 at a current density of 1 A g À 1 , and 277.8 mAh g À 1 at 10 A g À 1 . Most importantly, the NiCoSe 4 @NC retains a capacity of 293 mAh g À 1 at 1 A g À 1 after 1500 cycles, with a capacity decay rate of 0.025 % per cycle.

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