First Introduction of NiSe(2) to Anode Material for Sodium-Ion Batteries: A Hybrid of Graphene-Wrapped NiSe(2)/C Porous Nanofiber

The first-ever study of nickel selenide materials as efficient anode materials for Na-ion rechargeable batteries is conducted using the electrospinning process. NiSe(2)-reduced graphene oxide (rGO)-C composite nanofibers are successfully prepared via electrospinning and a subsequent selenization process. The electrospun nanofibers giving rise to these porous-structured composite nanofibers with optimum amount of amorphous C are obtained from the polystyrene to polyacrylonitrile ratio of 1/4. These composite nanofibers also consist of uniformly distributed single-crystalline NiSe(2) nanocrystals that have a mean size of 27 nm. In contrast, the densely structured bare NiSe(2) nanofibers formed via selenization of the pure NiO nanofibers consist of large crystallites. The initial discharge capacities of the NiSe(2)-rGO-C composite and bare NiSe(2) nanofibers at a current density of 200 mA g(−1) are 717 and 755 mA h g(−1), respectively. However, the respective 100(th)-cycle discharge capacities of the former and latter are 468 and 35 mA h g(−1). Electrochemical impedance spectroscopy measurements reveal the structural stability of the composite nanofibers during repeated Na-ion insertion and extraction processes. The excellent Na-ion storage properties of these nanofibers are attributed to this structural stability.