Etching‐in‐a‐Box: A Novel Strategy to Synthesize Unique Yolk‐Shelled Fe₃O₄@Carbon with an Ultralong Cycling Life for Lithium Storage

An etching-in-a-box strategy is developed to synthesize unique Fe3O4@C yolk-shelled nanocubes. Interestingly, inner cavities are generated in Fe3O4 cores during the etching process. With an optimized etching time of 2 h, an ultralong cycling life is achieved, in which even after 8000 cycles the material can still deliver a significant capacity of 475 mAh g−1 at 10 A g−1.