Thermodynamic Transformation of Crystalline Organic Hybrid Iron Selenide to Fe_xSe_y@CN Microrods for Sodium Ion Storage

Carbon-coated metal chalcogenide composites have been demonstrated as one type of promising anode material for sodium-ion batteries (SIBs). However, combining carbon materials with micronanoparticles of metal chalcogenide always involve complicated processes, such as polymer coating, carbonization, and sulfidation/selenization. To address this issue, herein, we reported a series of carbon-coated Fe_xSe_y@CN (Fe_xSe_y = FeSe₂, Fe₃Se₄, Fe₇Se₈) composites prepared via the thermodynamic transformation of a crystalline organic hybrid iron selenide [Fe(phen)₂](Se₄) (phen = 1,10-phenanthroline). By pyrolyzing the bulk crystals of [Fe(phen)2](Se4) at different temperatures, Fe_xSe_y microrods were formed in situ, where the nitrogen-doped carbon layers were coated on the surface of the microrods. Moreover, all the as-prepared Fe_xSe_y@CN composites exhibited excellent sodium-ion storage capabilities as anode materials in SIBs. This work proves that crystalline organic hybrid metal chalcogenides can be used as a novel material system for the in situ formation of carbon-coated metal chalcogenide composites, which could have great potential in the application of electrochemical energy storage.