\textit{Ab Initio}\textbf{ Studies of the Phase Transition Mechanism of MnO}$_{\mathrm{\mathbf{2}}}$\textbf{ Modified with Bi, Cu, and Mg in Rechargeable Zn/MnO}$_{\mathrm{\mathbf{2}}}$\textbf{ Batteries.}

Rechargeable alkaline Zn/MnO$_{\mathrm{2}}$ batteries hold great promise for electrical energy storage and power grid applications due to their high energy density, non-toxicity, and low cost. Bi and Cu additives are known to significantly extend the cycle life and increase the capacity of MnO$_{\mathrm{2}}$ electrodes in rechargeable Zn/MnO$_{\mathrm{2}}$ batteries. However, the mechanism of interaction of Bi and Cu with the MnO$_{\mathrm{2}}$ cathode material is not completely understood. To investigate the influence of chemical additives on the rechargeability and cyclability of MnO$_{\mathrm{2}}$ electrodes, we calculated the geometries and formation enthalpies for a wide variety of crystal structures of MnO$_{\mathrm{2}}$ modified with Bi, Cu, and Mg using \textit{ab initio} computational methods based on density functional theory. The results of our calculations suggest that reversible transitions between the layered and spinel phases could play an important role in the cycling mechanism of chemically modified MnO$_{\mathrm{2}}$ cathodes.