Electronic structure and optical spectra of novel rechargeable lithium batteries

Electronic spectra of promising materials for rechargeable lithium batteries, LiCr6 and LiMn2O4, have been studied. Theoretical calculations in combination with experiments for the pi* and sigma* x-ray absorption edges are reported for the pure graphite and the graphite intercalation compound, LiC6. The anisotropy of the absorption spectra is due to the difference in the optical matrix elements for two different polarizations, which is a result of the anisotropic crystallographic and electronic properties of LiC6. Theory and experiment agree well for the pi* and sigma* resonances. By comparing calculations which include the effect of the core hole with similar calculations which do not, we conclude that 1s x-ray absorption in LiC6 is partly associated with an excitonic effect. The electronic structure and optical absorption spectrum of LiMn2O4 spinel has been calculated and compared with available experimental data. The calculated absorption coefficient appeared to be in agreement with experiment, and the features of the absorption are associated with transitions between the exchange and crystal-field split t(2g), and e(g) d-bands of manganese in LiMn2O4 spinel.