Ternary Spinel MCo2O4 (M = Mn, Fe, Ni, and Zn) Porous Nanorods as Bifunctional Cathode Materials for Lithium–O2 Batteries

Abstract

The development of Li–O₂ battery electrocatalysts has been extensively explored recently. The Co₃O₄ oxide has attracted much attention because of its bifunctional activity and high abundance. In the present study, toxic Co²⁺ has been replaced through the substitution on the tetrahedral spinel A site ions with environmental friendly metals (Mn²⁺, Fe²⁺, Ni²⁺, and Zn²⁺), and porous nanorod structure are formed. Among these spinel MCo₂O₄ cathodes, the FeCo₂O₄ surface has the highest Co³⁺ ratio. Thus, oxygen can be easily adsorbed onto the active sites. In addition, Fe²⁺ in the tetrahedral site can easily release electrons to reduce oxygen and oxidize to half electron filled Fe³⁺. The FeCo₂O₄ cathode exhibits the highest discharging plateau and lowest charging plateau as shown by the charge–discharge profile. Moreover, the porous FeCo₂O₄ nanorods can also facilitate achieving high capacity and good cycling performance, which are beneficial for O₂ diffusion channels and Li₂O₂ formation/decomposition pathways.