Synthesis and Electrochemical Characterization of Zn2Mn3O8 Cathodes via MgO-Mediated Self-Sacrificial Phase Transformation for Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have gained considerable attention as safe, environmentally friendly, and cost-effective alternatives to conventional battery technologies. However, the use of toxic and costly vanadium-based cathode materials combined with manganese-based cathodes exhibiting relatively high synthesis costs has hindered their widespread commercial deployment. In this study, we explore the potential of magnesium oxide (MgO), a low-cost, abundant, and nontoxic material, as a sacrificial precursor cathode for AZIBs. Using various ex situ characterization techniques, it has been elucidated that MgO undergoes a self-sacrificial transformation into zinc manganese oxide (Zn₂Mn₃O₈), thereby endowing it with the capability to store zinc ions. Under the same testing conditions as those of other Mn-based cathodes, the MgO powder exhibited electrochemical behavior that required the cooperative participation of an appropriate amount of Mn²⁺ and Zn²⁺ during cycling to achieve superior rate performance. Furthermore, density functional theory (DFT) calculations and experimental results confirm that MgO undergoes a phase transition that enhances electrode zincophilic activity, improving the charge/discharge kinetics and stability. To further enhance its electrochemical performance, MgO nanosheets were grown in situ on carbon cloth (CC) as the precursor using an electrochemical deposition method, resulting in a significant improvement in the specific capacity from 329 to 736 mAh g^–1 (at 0.1 A g^–1) compared to the MgO powder precursor cathode. The MgO powder and MgO@CC precursor were transformed into Zn₂Mn₃O₈ cathodes denoted as MZMO and MZMO@CC, respectively. The MZMO@CC exhibits superior performance with a specific capacity of 736 mAh g^–1 (0.81 mAh cm^–2), excellent rate capability, and fair long-term stability. This research highlights the promising role of the MgO precursor in AZIBs, demonstrating both its high specific capacity and excellent reaction kinetics. This work offers new insights into the design of high-performance, low-cost, and environmentally benign cathode materials for AZIBs.