Influence of Surfaces on the Electrochemical Properties of MnO₂ in Rechargeable Zn/MnO₂ Batteries

Rechargeable alkaline Zn/MnO₂ batteries are well suited for large-scale electrical energy storage because of their high energy density, non-toxicity, and low cost. The performance of MnO₂ electrodes in rechargeable Zn/MnO₂ batteries can be enhanced by nanostructuring and by introducing defects into the crystal structure of MnO₂. However, the mechanism of this enhancement has not been investigated in detail. We apply ab initio density functional computational methods to study the mechanism of insertion of hydrogen ions into the structures of β-, R-, and γ-MnO₂ polymorphs. Our calculations show that the presence of surfaces significantly changes the binding energies of hydrogen ions inserted into the crystal structures of MnO₂ polymorphs. The energies of hydrogen ions attached to the surfaces and inserted just under the surfaces of β-, R-, and γ-MnO₂ polymorphs were found to be lower than those for bulk MnO₂. The results of our study indicate that the electrochemical properties of MnO₂ cathodes can be substantially influenced by nanostructuring.