Amorphous FeO/Graphene Composite Nanosheets with Enhanced Electrochemical Performance for Sodium-Ion Battery.

With the increasing use of sodium-ion batteries (SIBs), developing cost-effective anode materials, such as metal oxide, for Na-ion storage is one of the most attractive topics. Due to the obviously larger ion radius of Na than that of Li, most metal oxide electrode materials fail to exhibit the same high performance for SIBs like that of Li-ion batteries. Herein, iron oxide was employed to demonstrate a concept that rationally designing an amorphous structure should be useful to enhance Na-ion storage performance of a metal oxide. Amorphous FeO/graphene composite nanosheets (FeO@GNS) were successfully synthesized by a facile approach as anodes for SIBs. It reveals that amorphous FeO nanoparticles with an average diameter of 5 nm were uniformly anchored on the surface of graphene nanosheets by the strong C-O-Fe oxygen-bridge bond. Compared to well-crystalline FeO, amorphous FeO@GNS exhibited superior sodium storage properties such as high electrochemical activity, high initial Coulombic efficiency of 81.2%, and good rate performance. At a current density of 100 mA/g, amorphous FeO@GNS composites show a specific capacity of 440 mAh/g, which is obviously higher than the specific capacity of 284 mAh/g of crystalline FeO. Even at a high current density of 2 A/g, amorphous FeO@GNS composites still exhibit a specific capacity as high as 219 mAh/g. The excellent electrochemical performance should be attributed to the amorphous structures of FeO as well as strongly interfacial interaction between FeO and GNS, which not only accommodate more electrochemical active sites and provide the more transmission channels for sodium ions but also benefit electron transfer as well as effectively buffer the volume change of host materials during sodiation and desodiation. This concept for designing amorphous iron oxide anodes for SIBs is also expected to facilitate preparation of various amorphous nanostructure of other metal oxides and improve their Na-ion storage performance.