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 (Fe 3 O 4 ) 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 SnO 2 and nitrogen-doped carbon on Fe 3 O 4 yolk (denoted as Fe 3 O 4 @SnO 2 @C–N nanoboxes). The yolk–shell structured Fe 3 O 4 @SnO 2 @C–N nanoboxes have the adjustable void space, which permits the free expansion of Fe 3 O 4 yolks without breaking the double shells during the lithiation/delithiation processes, avoiding the structural pulverization. Moreover, the heterogeneous double-shelled SnO 2 @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 Fe 3 O 4 @SnO 2 @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.