Carbon encapsulated 3D hierarchical Fe3O4 spheres as advanced anode materials with long cycle lifetimes for lithium-ion batteries

As anode materials for lithium ion batteries, metal oxides have large storage capacity. However, their cycle life and rate capability are still not suitable for commercial applications. Herein, 3D hierarchical Fe3O4 spheres associated with a 5-10 nm carbon shell were designed and fabricated. In the constructed architecture, the thin carbon shells can avoid the direct exposure of encapsulated Fe3O4 to the electrolyte and preserve the structural and electrochemical integrity of spheres as well as inhibit the aggregation of pulverized Fe3O4 during electrochemical cycling. The hierarchical structure formed by the bottom-up self-assembly approach can efficiently accommodate the mechanical stress induced by the severe volume variation of Fe3O4 during lithiation-delithiation processes. Moreover, the carbon shell together with the structure integrity and durability endows the favorable high conductivity and efficient ion transport. All these features are critical for high-performance anodes, therefore enabling an outstanding lithium storage performance with a long cycle lifespan. For instance, such an electrode could deliver a capacity of 910 mA h g(-1) even after 600 cycles with a discharge-charge rate of 1 A g(-1). In addition, this effective strategy may be readily extended to construct many other classes of hybrid electrode materials for high-performance lithium-ion batteries.