A Computational and Spectroscopic Study of the Electronic Structure of V2O5-Based Cathode Materials

The electronic structure of alpha-V2O5, gamma'-V2O5, and gamma-MeV2O5 (Me = Li, Na) bronzes is studied by quantum-chemical calculations completed by spectroscopic experiments. The calculations are performed using the G(0)W(0) method with the DFT+U self-consistent wave function as an initial approximation. The electronic band gap E-g = 2.89 eV calculated for alpha-V2O5 is found to be in fair agreement with available experimental data. The strategy was then applied to studying the electronic structure of the. gamma'-V2O5 phase and gamma-MeV2O5 bronzes for which no experimental band gap data exist in the literature. Computed E-g values are equal to 3.17, 1.21 and 1.18 eV for gamma'-V2O5, gamma-LiV2O5, and gamma-NaV2O5, respectively. The nature of the alkali metal atom is determined to have little influence on the structure and electronic states of the bronzes. Raman spectra recorded with different wavelengths of exciting radiation have allowed the determination of the energy threshold corresponding to the transition from off-resonance to resonance Raman scattering process. In this way, a band gap value in the range 2.54-2.71 eV for alpha-V2O5 and gamma'-V2O5 is obtained in good agreement with the experimental values for the alpha-phase. Raman spectra of gamma-MeV2O5 suggest the band gap smaller than 1.58 eV in these materials, whereas the photoluminescence measurements yield E-g approximate to 0.95 eV for the gamma-LiV2O5 bronze. Remarkably, the result of the G(0)W(0) calculations lies in between the experimental estimates. The strong similarity of structures and electronic states of gamma-LiV2O5 and gamma-NaV2O5 accounts for their the same operating voltage when used as cathodes in Li(Na)-ion batteries.