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

Manganese oxide (MnO) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO) allows reversible insertion/extraction of Zn ions and exhibits high storage capacity of Zn ions. However, a poor conductivity of δ-MnO, as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO 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-MnO nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn 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-MnO cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO. The results obtained pave the way for improving the electrical conductivity of MnO 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.