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

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.