First Principles Calculations of Formation Energies and Electronic Structures of Defects in Oxygen-Deficient LiMn[sub 2]O[sub 4]

Abstract

The formation energies of many kinds of defects for oxygen-deficient LiMn 2 O 4 , including both oxygen-vacancy types and metalinterstitial types, have been determined by first principles plane-wave pseudopotential calculations. Two kinds of metal-excess defects show the lowest formation energies. They were found to be more stable than the simple oxygen vacancy that exhibits the lowest formation energy among oxygen-vacancy-type defects. In both of the metal-excess defects with the lowest formation energies, excess Li occupies an empty 16c position of spinel. Excess Mn is present either at the 8a position, substituting for Li, or at the empty 16c position, moving one neighboring Li into the next 16c position. The results are consistent with experimental results of density measurements, diffusion experiments, and decomposition reactions at high temperatures. Detailed examination of the electronic structures revealed that formal charges of both interstitial and substituted Mn are ϩ2.

Jahn–Teller distortion and electronic structure of LiMn2O4

“…GGA results show that LiMn 2 O 4 is metallic (Fig. 3a), which is the same as reports in literature [10][11][12][13]. The fermi level crosses the conduction band and the lower part of the conduction band becomes filled.…”

“…Absorption spectroscopic measurements show that the band gap of pulsed laser deposition prepared LiMn 2 O 4 film is around 1 eV [8,9]. However, the experiment observed semiconducting characteristics of the LiMn 2 O 4 compound is not in agreement with recent first principles calculated electronic structures [10][11][12][13], which are shown to be metallic, and Mn ions in LiMn 2 O 4 are Mn 3.5+ . This is also contradictory to the X-ray absorption spectroscopy and neutron diffraction results [14][15][16].…”

Inequality of quenched and high temperature structure of lithium deficient LiMn2O4

“…Both unit-cell parameter and fractional manganese occupancy of tetrahedral sites lead to the conclusion, that above 1045 K manganese ions migrate to the tetrahedral positions and reduce their oxidation state to +2. This effect corresponds well to the theoretical predictions reported earlier [28] and to the lattice constant dependence on the LiMn 2 O 4 synthesis temperature [17,26].…”

“…These results reveal that to control the 8a site oc- The open question remains where the Li ions pushed out from the 8a sites by Mn ions are located. There are two possibilities, both suggested by experiment and theoretical predictions [17,28]: 1) Li ions locate in the lithium-rich additional phase such as Li 2 MnO 3 , 2) Li ions locate on the 16c spinel site. The planned neutron diffraction measurements should solve the problem.…”

A review of conduction phenomena in Li-ion batteries

“…First-principles calculations [62,104,105,[131][132][133] can be a powerful tool for understanding atomic scale diffusion in cathode particles and providing detailed insight into diffusion mechanisms and structural properties. First-principles calculations of Li x CoO 2 diffusivity have been conducted at varying intercalation levels of Li (0 ≤ x ≤ 1), elucidating the reason for the wide variation of diffusivity based upon the activation barrier change and divacancy diffusion mechanisms (also, see Table 7) [131,134].…”