DOE OSTI2020
Li3Fe2(CoO4)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with six equivalent FeO6 octahedra, edges with two equivalent FeO6 octahedra, edges with four LiO6 octahedra, and edges with four CoO6 octahedra. The corner-sharing octahedra tilt angles range from 4–11°. There are a spread of Li–O bond distances ranging from 2.12–2.15 Å. In the second Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with six equivalent FeO6 octahedra, edges with two equivalent FeO6 octahedra, edges with four LiO6 octahedra, and edges with four CoO6 octahedra. The corner-sharing octahedra tilt angles range from 4–11°. There are two shorter (2.13 Å) and four longer (2.14 Å) Li–O bond lengths. In the third Li1+ site, Li1+ is bonded to six O2- atoms to form LiO6 octahedra that share corners with six equivalent CoO6 octahedra, edges with two equivalent CoO6 octahedra, edges with four LiO6 octahedra, and edges with four FeO6 octahedra. The corner-sharing octahedra tilt angles range from 5–10°. There are a spread of Li–O bond distances ranging from 2.12–2.18 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six equivalent LiO6 octahedra, edges with two equivalent FeO6 octahedra, edges with four LiO6 octahedra, and edges with four CoO6 octahedra. The corner-sharing octahedra tilt angles range from 4–11°. There are two shorter (2.03 Å) and four longer (2.06 Å) Fe–O bond lengths. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six equivalent LiO6 octahedra, edges with two equivalent FeO6 octahedra, edges with four LiO6 octahedra, and edges with four CoO6 octahedra. The corner-sharing octahedra tilt angles range from 4–11°. There are two shorter (2.03 Å) and four longer (2.06 Å) Fe–O bond lengths. There are two inequivalent Co+3.50+ sites. In the first Co+3.50+ site, Co+3.50+ is bonded to six O2- atoms to form CoO6 octahedra that share edges with two equivalent CoO6 octahedra, edges with four FeO6 octahedra, and edges with six LiO6 octahedra. All Co–O bond lengths are 1.91 Å. In the second Co+3.50+ site, Co+3.50+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with six equivalent LiO6 octahedra, edges with two equivalent CoO6 octahedra, edges with four LiO6 octahedra, and edges with four FeO6 octahedra. The corner-sharing octahedra tilt angles range from 5–10°. There are a spread of Co–O bond distances ranging from 2.02–2.05 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to two Li1+, one Fe3+, and two Co+3.50+ atoms to form OLi2FeCo2 square pyramids that share corners with nine OLi2Fe2Co square pyramids, edges with four equivalent OLi3Fe2Co octahedra, and edges with four OLi2Fe2Co square pyramids. In the second O2- site, O2- is bonded to two Li1+, two Fe3+, and one Co+3.50+ atom to form OLi2Fe2Co square pyramids that share corners with nine OLi2Fe2Co square pyramids, edges with four equivalent OLi3Fe2Co octahedra, and edges with four OLi2FeCo2 square pyramids. In the third O2- site, O2- is bonded to two Li1+, one Fe3+, and two Co+3.50+ atoms to form OLi2FeCo2 square pyramids that share corners with nine OLi2Fe2Co square pyramids, edges with four equivalent OLi3Fe2Co octahedra, and edges with four OLi2Fe2Co square pyramids. In the fourth O2- site, O2- is bonded to three Li1+, two Fe3+, and one Co+3.50+ atom to form OLi3Fe2Co octahedra that share corners with six equivalent OLi3Fe2Co octahedra and edges with twelve OLi2Fe2Co square pyramids. The corner-sharing octahedral tilt angles are 0°.