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Materials Data on Li8MnO6 by Materials Project

Li8MnO6 crystallizes in the hexagonal P6_3cm space group. The structure is three-dimensional. there are three inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with two equivalent MnO4 tetrahedra, corners with six equivalent LiO4 tetrahedra, corners with four equivalent LiO4 trigonal pyramids, edges with two equivalent LiO4 tetrahedra, and edges with three equivalent LiO4 trigonal pyramids. There are two shorter (1.99 Å) and two longer (2.01 Å) Li–O bond lengths. In the second Li1+ site, Li1+ is bonded to four O2- atoms to form distorted LiO4 trigonal pyramids that share corners with eight LiO4 tetrahedra, corners with six equivalent LiO4 trigonal pyramids, an edgeedge with one MnO4 tetrahedra, and edges with three equivalent LiO4 tetrahedra. There are a spread of Li–O bond distances ranging from 1.98–2.17 Å. In the third Li1+ site, Li1+ is bonded to four O2- atoms to form LiO4 tetrahedra that share corners with three equivalent LiO4 tetrahedra, corners with three equivalent MnO4 tetrahedra, corners with six equivalent LiO4 trigonal pyramids, and edges with three equivalent LiO4 tetrahedra. There are three shorter (1.98 Å) and one longer (2.04 Å) Li–O bond lengths. Mn4+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with twelve LiO4 tetrahedra and edges with three equivalent LiO4 trigonal pyramids. There is three shorter (1.77 Å) and one longer (1.96 Å) Mn–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four Li1+ and one Mn4+ atom to form corner-sharing OLi4Mn trigonal bipyramids. In the second O2- site, O2- is bonded in a 7-coordinate geometry to seven Li1+ atoms. In the third O2- site, O2- is bonded in a 7-coordinate geometry to six Li1+ and one Mn4+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Li8MnO6 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗

Li 8 MnO 6 : A Novel Cathode Material with Only Anionic Redox

In Li-excess transition-metal-oxide cathode materials, anionic oxygen redox can offer high capacity and high voltages, although peroxo and superoxo species may cause oxygen loss, poor cycling performance, and capacity fading. Previous work showed that undesirable formation of peroxide and superoxide bonds is controlled to some extent by Mn substitution, and the present work uses density functional calculations to examine the reasons for this by studying the anionic redox mechanism Li 8 MnO 6 . This material is obtained by substituting Mn for Sn in Li 8 SnO 6 or for Zr in Li 8 ZrO 6 , and we also compare to previous work on those materials. The calculations predict that Li 8 MnO 6 is stable at room temperature (with a band gap of 3.19 eV as calculated HSE06 and 1.82 eV as calculated with the less reliable with PBE+U), and they elucidate the chemical and structural effects involved in the inhibition of oxygen release in this cathode. Throughout the whole delithiation process, only O 2- ions are oxidized. The directional Mn-O bonds formed from unfilled 3d orbitals effectively inhibit the formation of O-O bonds, and the layered structure is maintained even after removing 3 Li per Li 8 MnO 6 formula unit. The calculated average voltage for removal of 3 Li is 3.69 V by HSE06, and the corresponding capacity is 389 mAh/g. The high voltage of oxygen anionic redox and the high capacity result in a high energy density of 1436 Wh/kg. The Li-ion diffusion barrier for the dominant interlayer diffusion path along the c-axis is 0.57 eV by PBE+U. Finally, these results help us to understand the oxygen redox mechanism in a new lithium-rich Li 8 MnO 6 cathode material and contribute to the design of high-energy-density lithium-ion-battery cathode materials with favorable electrochemical properties based on anionic oxygen redox.

Li8MnO6↗