Prussion Blue-Supported Annealing Chemical Reaction Route Synthesized Double-Shelled Fe₂O₃/Co₃O₄ Hollow Microcubes as Anode Materials for Lithium-Ion Battery

Fe₂O₃/Co₃O₄ double-shelled hierarchical microcubes were synthesized based on annealing of double-shelled Fe₄[Fe­(CN)₆]₃/Co­(OH)₂ microcubes, using Co­(AC)₂ as a Co²⁺ source to react with OH^– generated from the reaction of ammonium hydroxide and water. The robust Fe₂O₃ hollow microcube at the inner layer not only displays a good electronic conductivity but also acts as stable supports for hierarchical Co₃O₄ outside shell consisting of nanosized particles. The double-shelled hollow structured Fe₂O₃/Co₃O₄ nanocomposites display obvious advantages as anode materials for LIBs. The hollow structure can ensure the presence of additional free volume to alleviate the structural strain associated with repeated Li⁺-insertion/extraction processes, as well as a good contact between electrode and electrolyte. The robust Fe₂O₃ shell acts as a strong support for Co₃O₄ nanoparticles and efficiently prevents the aggregation of the Co₃O₄ nanoparticles. Furthermore, the charge transfer resistance can be greatly decreased because of the formation of interface between Fe₂O₃ and Co₃O₄ shells and a relative good electronic conductivity of Fe₂O₃ than that of Co₃O₄, resulting in a decrease of charge transfer resistance for improving the electron kinetics for the hollow double-shelled microcube as anode materials for LIBs. The Fe₂O₃/Co₃O₄ nanocomposite anode with a molar ratio of 1:1 for Fe:Co exhibits the best cycle performance, displaying an initial Coulombic efficiency of 74.4%, delivering a specific capacity of 500 mAh g^–1 after 50 cycles at a current density of 100 mA g^–1, 3 times higher than that of pure Co₃O₄ nanoparticle sample. The great improvement of the electrochemical performance of the synthesized Fe₂O₃/Co₃O₄ double-shelled hollow microcubes can be attributed to the unique microstructure characteristics and synergistic effect between the inner shell of Fe₂O₃ and outer shell of Co₃O₄.