Hydrolysis-Coupled Redox Reaction to 3D Cu/Fe₃O₄ Nanorod Array Electrodes for High-Performance Lithium-Ion Batteries

A facile hydrolysis-coupled redox (HCR) reaction followed by postheating reduction has been designed to prepare unique 3D Cu/Fe₃O₄ core-shell nanorod array anodes. Fe²⁺ ions from fresh FeSO₄ solution have been hydrolyzed and oxidized to form an Fe(OH)₃ shell on the surface of Cu(OH)₂ nanorods; meanwhile the resulting acidic environment induces the reduction of Cu(OH)₂ to Cu₂O, which realizes an unusual redox reaction between Fe²⁺ ions and Cu(OH)₂. The reaction procedure and thermodynamics possibility between Fe²⁺ ions and Cu(OH)₂ nanorod arrays are discussed from the aspect of electrode potentials. After postheating reduction in Ar/H₂, the obtained 3D architecture of Cu current collector serves as a stout support for the Fe₃O₄ shell to form nanorod array anodes without using any binders or conducting agents. The resulting highly stable core-shell structure facilitates rapid and high-throughput transport pathways for ions/electrons and allows better accommodation of volume change during the repeated lithiation/delithiation. Its application as anodes in combination with LiNi_0.5Mn_1.5O₄ cathodes for full cells demonstrates superior rate capability, enhanced energy density, and long cycling life.