Influence of Structural Defects on the Electrochemical Properties of MnO₂ in Rechargeable Zn/MnO₂ Alkaline Batteries: An <i>Ab Initio</i> Study

Electrical energy storage is essential for seamless integration of intermittent renewable energy sources into the power grid. Rechargeable alkaline Zn/MnO₂ batteries are attractive for large-scale electrical energy storage due to their high energy density, non-toxicity and low cost. The performance of MnO₂ electrodes in Zn/MnO₂ batteries can be enhanced by nanostructuring and by introducing defects into the crystal structure of MnO₂. However, the mechanism of this enhancement is not fully understood. We apply first-principles computational methods based on density functional theory to study the mechanism of hydrogen ion insertion into the crystal structures of pyrolusite (β), ramsdellite (R), and nsutite (γ) MnO₂ polymorphs containing oxygen and cation vacancies. Our calculations show that the presence of oxygen and cation vacancies significantly changes the binding energies of hydrogen ions inserted into the structures of MnO₂ polymorphs. The results of our study could explain the influence of structural defects on the electrochemical properties of MnO2 in rechargeable Zn/MnO2 batteries.