An ab initio Study of Reduction of V₂O₅ through the Formation of Oxygen Vacancies and Li Intercalation

Abstract

Two methods of reduction of V 2 O 5 have been investigated: oxygen vacancy formation and lithium intercalation. The electronic structure, geometry, and energetics of these reduced systems are examined. Oxygen vacancies in bulk R-V 2 O 5 have been investigated by using gradient-corrected density functional theory (GGA) and density functional theory corrected for on-site Coulomb interactions in strongly correlated systems (GGA+U). The GGA calculation predicts a delocalized defect electronic state. This disagrees with experimental evidence, which indicates that oxygen vacancies produce a localized reduced vanadium state in the band gap. The DFT+U results for U ) 4.0 eV are consistent with available UPS and XPS data, indicating strong localization on the vanadium atoms nearest the vacancy, and showing reduced V(IV) species. Intercalation of Li in V 2 O 5 , which has important potential applications in energy storage devices, is also reported at the GGA+U level, using the value of U obtained from the oxygen-deficient calculation, and localized reduction is demonstrated. These results are again in agreement with available UPS data and crystallographic data, indicating good transferability of this value of U among the systems of interest. Calculated lithium intercalation energies for both the Rand γ-V 2 O 5 phases are reported, and the structure and relative stability of the deintercalated γ-V 2 O 5 phase are also examined.

The electronic structure of the antimony chalcogenide series: Prospects for optoelectronic applications

“…In contrast, an early optical study reported an optical band gap of approximately 4.0 eV resulting from indirect transitions [1]. The calculated optical band gap in this study is in good agreement with the low end of the experimental range, consistent with the PBE functional (and other GGA functionals) underestimating band gaps [104]. …”

GGA+Udescription of lithium intercalation into anataseTiO2

“…These predictions of metallic behavior are incompatible with the localized defect state indicated by experimental photoabsorption 10 and disagree qualitatively with previous Hartree-Fock calculations. 48 Standard DFT functionals ͑local density or general gradient approximations͒ often fail to predict correct electronic structures for reduced transition metal oxides, [58][59][60] due to the self-interaction error inherent to such functionals, 61,62 and which is acute for highly localized d and f valence states. This has been discussed previously for a number of reduced TiO 2 systems.…”

“…64 This opens a gap between occupied and unoccupied states for the orbitals of interest and gives improved descriptions of polaronic defect states in a number of oxides. [59][60][61]65 Richter et al 66 have previously demonstrated that GGA+ U reproduces the experimental splitting between occupied and unoccupied Ti 3d states in lithium titanate ͑Li 0.5 TiO 2 ͒, although the corresponding charge density was not presented, and this method has not yet been applied to the low concentration lithiated-anatase phase.…”

Defect-induced Burstein-Moss shift in reduced V2O5 nanostructures

“…Reduction of V 2 O 5 through the formation of oxygen vacancy, V O , defects have been studied both by theoretical and experimental studies. 10,11,12,13,14,15 In this work, we address some of the key unanswered questions regarding the correlation between optical properties and electronic structure of The rise of absorbance in the NIR spectral range in reduced oxide is a result of optical excitation of V O defect related mid-gap states. In addition, using in-situ Raman measurements during reduction process, we show that the oxygen atom that most readily participates during electrochemical reduction at room-temperature and gets reduced is the three-fold coordinated oxygen (O3).…”