Synthesis of Uniquely Structured Yolk-Shell Metal Oxide Microspheres Filled with Nitrogen-Doped Graphitic Carbon with Excellent Li-Ion Storage Performance

Novel structured composite microspheres of metal oxide and nitrogen-doped graphitic carbon (NGC) have been developed as efficient anode materials for lithium-ion batteries. A new strategy is first applied to a one-pot preparation of composite (FeOx-NGC/Y) microspheres via spray pyrolysis. The FeOx-NGC/Y composite microspheres have a yolk-shell structure based on the iron oxide material. The void space of the yolk-shell microsphere is filled with NGC. Dicyandiamide additive plays a key role in the formation of the FeOx-NGC/Y composite microspheres by inducing Ostwald ripening to form a yolk-shell structure based on the iron oxide material. The FeOx-NGC/Y composite microspheres with the mixed crystal structure of rock salt FeO and spinel Fe3O4 phases show highly superior lithium-ion storage performances compared to the dense-structured FeOx microspheres with and without carbon material. The discharge capacities of the FeOx-NGC/Y microspheres for the 1st and 1000th cycle at 1 A g(-1) are 1423 and 1071 mAh g(-1), respectively. The microspheres have a reversible discharge capacity of 598 mAh g(-1) at an extremely high current density of 10 A g(-1). Furthermore, the strategy described in this study is generally applied to multicomponent metal oxide-carbon composite microspheres with yolk-shell structures based on metal oxide materials.