Discharging Behavior of Hollandite α-MnO2 in a Hydrated Zinc-Ion Battery

Hollandite, alpha-MnO2, is of interest as a prospective cathode material for hydrated zinc-ion batteries (ZIBs); however, the mechanistic understanding of the discharge process remains limited. Herein, a systematic study on the initial discharge of an alpha-MnO2 cathode under a hydrated environment was reported using density functional theory (DFT) in combination with complementary experiments, where the DFT predictions well described the experimental measurements on discharge voltages and manganese oxidation states. According to the DFT calculations, both protons (H+) and zinc ions (Zn2+) contribute to the discharging potentials of alpha-MnO2 observed experimentally, where the presence of water plays an essential role during the process. This study provides valuable insights into the mechanistic understanding of the discharge of alpha-MnO2 in hydrated ZIBs, emphasizing the crucial interplay among the H2O molecules, the intercalated Zn2+ or H+ ions, and the Mn4+ ions on the tunnel wall to enhance the stability of discharged states and, thus, the electrochemical performances in hydrated ZIBs.

Automated summary

The study systematically investigated the initial discharge process of α-MnO2 cathode in a hydrated environment using DFT and experiments, revealing the essential role of water in the discharge process; DFT calculations suggest that both protons and zinc ions contribute to the discharge potentials of α-MnO2 observed experimentally.