First Principles Investigation on the Phase Change Induced By Delithiation of Li2Fe0.5Mn0.5SiO4

In this work, the phase change induced by the delithiation of Li₂Fe_0.5Mn_0.5SiO₄ compound is investigated via the First Principles calculations. Three delithiated states are selected to calculate their formation energies and crystal structures. The calculated results reveal that there is a significant difference in phase structures between the LiFe_0.5Mn_0.5SiO₄ and Li_0.5Fe_0.5Mn_0.5SiO₄ compounds with severe volume variation. It is found that the local structures of Li₂Fe_0.5Mn_0.5SiO₄ compound is transformed from the corner-sharing tetrahedrons centered by Fe and Mn into the deformed hexahedrons in which Mn and Fe ions are connected to five O ions. The accompanied redox couples are Fe²⁺/Fe³⁺, Mn²⁺/Mn³⁺, and Mn³⁺/Mn⁴⁺ for the delithiation of Li₂Fe_0.5Mn_0.5SiO₄ to Li_1.5Fe_0.5Mn_0.5SiO₄, LiFe_0.5Mn_0.5SiO₄, and Li_0.5Fe_0.5Mn_0.5SiO₄, respectively.