MOF-Derived Mn₃O₄@C Hierarchical Nanospheres as Cathodes for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are potential electrochemical storage systems due to their safety, low cost, senior energy density, and environmental friendliness. There are no suitable cathode materials with cyclic stability due to the high polarization of Zn2+ ions, so synthesizing cathode materials with excellent electrochemical performance is still a problem to be solved. Mn3O4 is a potential cathode material owing to its abundant valence states. Nevertheless, it has poor cycling performance due to the disproportionation effect of Mn2+. Herein, we synthesize Mn3O4@C hierarchical nanospheres successfully using a Mn metal–organic framework via a simple hydrothermal synthesis method combined with a heat treatment process. Benefiting from the carbon coating, the Mn3O4@C cathode has a higher specific capacity of 331.5 mAh g–1 at 0.2 A g–1 (124.3 mAh g–1 at 3.0 A g–1) and satisfactory cyclic stability after 1900 cycles. The energy storage mechanism of insertion/extraction of H+ and Zn2+ is investigated by ex situ X-ray photoelectron spectroscopy. These results demonstrate a strategy to improve the manganese oxide cathode by the carbon coating for aqueous zinc-ion batteries.