δ-MnO2 nanoflower/graphite cathode for rechargeable aqueous zinc ion batteries.

Manganese oxide (MnO₂) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO₂) allows reversible insertion/extraction of Zn²⁺ ions and exhibits high storage capacity of Zn²⁺ ions. However, a poor conductivity of δ-MnO₂, as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO₂ with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO₂ nanoflowers and MNG were synthesized and examined using X-ray diffraction, electron spectroscopy, and electrochemical techniques. Also, performances of the batteries with the pristine δ-MnO₂ nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn²⁺ ions with diffusion scheme and pseudocapacitive behavior. The battery using MNG cathode exhibited a high initial discharge capacity of 235 mAh/g at 200 mA/g specific current density compared to 130 mAh/g which is displayed by the pristine δ-MnO₂ cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO₂. The results obtained pave the way for improving the electrical conductivity of MnO₂ by using graphite flake support. The graphite flake support significantly improved performances of ZIBs and made them attractive for use in a wide variety of energy applications. [ABSTRACT FROM AUTHOR]