Heterogeneous Double-Shelled Constructed Fe3O4 Yolk–Shell Magnetite Nanoboxes with Superior Lithium Storage Performances

Among the numerous candidate materials for lithium ion batteries, ferroferric oxide (Fe3O4) has been extensively concerned as a prospective anode material because of its high theoretical specific capacity, abundant resources, low cost, and nontoxicity. Here, we designed and fabricated a unique yolk-shell construction by generating heterogeneous double-shelled SnO2 and nitrogen-doped carbon on Fe3O4 yolk (denoted as Fe3O4@SnO2@C-N nanoboxes). The yolk-shell structured Fe3O4@SnO2@C-N nanoboxes have the adjustable void space, which permits the free expansion of Fe3O4 yolks without breaking the double shells during the lithiation/delithiation processes, avoiding the structural pulverization. Moreover, the heterogeneous double-shelled SnO2@C-N can meaningfully improve the electronic conductivity and enhance the lithium storage performance. Two metal oxides also show the specific synergistic effect, promoting the electrochemistry reaction. As a result, this yolk-shell structured Fe3O4@SnO2@C-N exhibits high specific capacity (870 mA h g-1 at 0.5 A g-1 after 200 cycles), superior rate capability, and long cycle life (670 mA h g-1 at 3 A g-1 after 600 cycles). This design and construction method can be extended to synthesize other yolk-shell nanostructured anode materials with improved electrochemistry performance.