Tailoring aqueous electrolytes based on M = Li, Na and K for the a-MnO2 electrode and its applications for energy storage devices: A DFT approach

Manganese oxide (MnO2) as an electrode material in energy storage devices has been used in supercapacitor electrodes because of its high capacitance and its sensitivity to the electrolyte chosen. In this work, density functional theory (DFT) calculations have been performed to understand the influence of the electrolyte MNO3 with different metal cations (M=Li, Na, K) and the presence of water molecules on the a-MnO2 surface. Through exploration of the potential energy surface, the relative energies involved in the diffusion process of M cations were described. The electronic density of states and the charge density differences allowed us to identify that the KNO3 electrolyte improves charge accumulation in the a-MnO2 structure. Quantum capacitance was calculated as an additional descriptor to elucidate the influence of the electronic structure properties on a-MnO2 during the charging process. This theoretical modeling provides a comprehensive framework for understanding the mechanisms behind the ion charge transfer within the electrolyte. In particular, its interaction with the surface of the electrodes and the related pseudocapacitive properties. This work also provides insight into the charge/discharge processes of the electrode at the atomic level and may serve as a tool to tailor novel materials for energy storage devices.