Determining the crystal and electronic structures of the magnesium secondary battery cathode material MgCo2−xMnxO4 using first-principles calculations and a quantum beam during discharge

Theoretical Study Using First-Principles Calculations of the Electronic Structures of Magnesium Secondary Battery Cathode Materials MgCo₂₋<i>_x</i>Mn<i>_x</i>O₄ (<i>x</i> = 0, 0.5) in the Pristine and Discharged States

“…The stable structures of pristine and discharged Mg 1+y Co 2−x Mn x O 4 (x = 0, 0.5; y = 0, 0.5, 0.75) are referenced from previous studies, 25,26 for Co and Mn atoms in this model. 18 A plane-wave cutoff energy of 550 eV was selected, and a k-point mesh of 1×1×1 or 7×7×7 was used for the structural calculation and the PDOS calculation, respectively.…”

“…23,24 Although the Mg/Co mixed-cation spinel model of MgCo 2−x Mn x O 4 (x = 0, 0.5) was not found to be more stable than the model of the normal spinel structure, the mixed-cation spinel-based model eventually became more stable than the normal spinel model with increasing Mg 2+ -ion insertion during discharge. 25,26 We therefore investigated the electronic structures of the Mg/Co mixed-cation spinel and the normal spinel models in the present study. are listed in Table 1.…”

“…5(b), although all of the Mg atoms on the 8a sites migrate to vacant 16c sites, some of the Co atoms remain on the 8a sites. In previous study26 , because the electron density and bond strength of Co-O bond is higher and stronger than that of Mg-O bond, it was reported that the Mg on the 8a site tends to move to the 16c site more than Co atom during discharge. Therefore, a part of Co atom remains on the 8a site though all Mg on the 8a site move to the 16c site 26.…”

“…3(b)migrate to the vacant 16c sites, some of the Mg atoms remain on the 8a sites. We previously reported that Mg was inserted into the vacant 16c sites near Mn and that the structural change from the spinel to the rocksalt structure occurred near Mn atoms 26. All of the Mg atoms on the 8a sites are completely moved to the 16c sites and the complete rocksalt structure is formed at the composition Mg 2 Co 1.5 Mn 0.5 O 4(Fig.…”

“…24 Other authors have reported investigations based on first-principles calculations of the stable structures of MgCo 2 O 4 and MgCo 1.5 Mn 0.5 O 4 in their pristine and discharged states. 25,26 In these computational studies, Mg 2+ ions occupying tetrahedral (8a) sites were reported to migrate to vacant (16c) sites when Mg 2+ ions were inserted into the vacant 16c sites in spinel-structured MgCo 2−x Mn x O 4 , which led to a structural change from the spinel to the rocksalt structure during discharge. 26 Although the mechanism of the structural change of MgCo 2−x Mn x O 4 (x = 0, 0.5) during the discharge process has been elucidated, the changes in electronic properties, such as the spin state and the valence state, during the discharge process remain unclear.…”