Pom-Pom Flower-like Morphology of δ-MnO2 with Superior Electrochemical Performances for Rechargeable Aqueous Zinc Ion Batteries

Abstract

A rechargeable aqueous zinc-ion battery is an encouraging alternative for grid-scale energy storage applications, owing to its advantages of high safety, low cost, and environmental benignity. Since MnO2 is found to be one of the most efficient intercalation cathode materials for ZIBs, the layered type δ-MnO2 polymorph exhibits reversible intercalation/de-intercalation of Zn2+ ions with a high capacity. Unfortunately, the δ-MnO2 cathode suffers from poor cyclability, low-rate capability, and structural degradation during charge–discharge cycles. Therefore, δ-MnO2 with Pom-Pom Flower-like morphology have been synthesized using a facile hydrothermal method. The unique morphology of δ-MnO2 provides a high surface area with numerous reaction sites, leading to excellent electrochemical performance. The obtained results revealed that the δ-MnO2 electrode retained ~99% of its initial capacity even after 250 cycles, which can be ascribed to the reversible Zn2+ insertion/de-insertion from the current unique morphology of the layered δ-MnO2 nanostructure. In addition, the electrochemical and structural investigation also indicates a two-step co-insertion of H+ and Zn2+ ions into the interlayer of δ-MnO2 during the discharge process. Thus, the superior electrochemical performances of the δ-MnO2 cathode paves a way for the high capacity and a long lifespan of zinc-ion batteries.