Crystal and electronic structures of Cr3O8 and LiCr3O8:: Probable cathode materials in Li batteries

Ground-state crystal structures are predicted for Cr3O8 and LiCr3O8 from accurate first-principles density-functional calculations by considering several (25 for the former and 12 for the latter phase) related structure types. Both phases stabilize in monoclinic (C2/m) structures with slight variations in the atomic arrangement of the chromium-oxygen framework. Structural optimization is also performed for Cr8O21, the obtained structural parameters being in good agreement with the experimental values. A possible synthesis route for Cr3O8 is suggested from total energy studies. Electronic structure studies indicate insulating behavior with very small band gaps for Cr8O21 and LiCr3O8 whereas Cr3O8 has pseudogaplike feature. Magnetic property and partial density of states analyses indicate two different valence states for Cr in all studied phases (except CrO3). Bonding characteristics and effects of Li intercalation in Cr3O8 are also analyzed with the help of charge density and charge transfer plots.