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 LiNi0.5Mn1.5O4 cathodes for full cells demonstrates superior rate capability, enhanced energy density, and long cycling life.