Phase-Dependent Properties of Manganese Oxides and Applications in Electrovoltaics

This study reports first-principles predictions as well as experimental synthesis of manganese oxide nanoparticles under different conditions. The theoretical part of the work comprised density functional theory (DFT)-based calculations and first-principles molecular dynamics (MD) simulations. The extensive research efforts and the current challenges in enhancing the performance of the lithium-ion battery (LIB) provided motivation to explore the potential of these materials for use as an anode in the battery. The structural analysis of the synthesized samples carried out using X-ray diffraction (XRD) confirmed the tetragonal structure of Mn₃O₄ on heating at 450 and 550 °C and the cubic structure of Mn₂O₃ on heating at 650 °C. The structures are found in the form of nanoparticles at 450 and 550 °C, but at 650 °C, the material appeared in the form of a nanoporous structure. Further, we investigated the electrochemical functionality of Mn₂O₃ and Mn₃O₄ as anode materials for utilization in LIBs via MD simulations. Based on the investigations of their electrical, structural, diffusion, and storage behavior, the anodic character of Mn₂O₃ and Mn₃O₄ is predicted. The findings indicated that 10 lithium atoms adsorb on Mn₂O₃, whereas 5 lithium atoms adsorb on Mn₃O₄ when saturation is taken into account. The storage capacities of Mn₂O₃ and Mn₃O₄ are estimated to be 1697 and 585 mAh g^-1, respectively. The maximum value of lithium insertion voltage per Li in Mn₂O₃ is 0.93 and 0.22 V in Mn₃O₄. Further, the diffusion coefficient values are found as 2.69 × 10^-9 and 2.65 × 10^-10 m² s^-1 for Mn₂O₃ and Mn₃O₄, respectively, at 300 K. The climbing image nudged elastic band method (Cl-NEB) was implemented, which revealed activation energy barriers of Li as 0.30 and 0.75 eV for Mn₂O₃ and Mn₃O₄, respectively. The findings of the work revealed high specific capacity, low Li diffusion energy barrier, and low open circuit voltage for the Mn₂O₃-based anode for use in LIBs.