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

Abstract 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 (FeO_x‐NGC/Y) microspheres via spray pyrolysis. The FeO_x‐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 FeO_x‐NGC/Y composite microspheres by inducing Ostwald ripening to form a yolk–shell structure based on the iron oxide material. The FeO_x‐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 FeO_x microspheres with and without carbon material. The discharge capacities of the FeO_x‐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.