No abstract

No abstract

Due to its exceptional lithium storage capacity silicon is considered as a promising candidate for anode material in lithium-ion batteries (LIBs). In the present work we demonstrate that methods of the soft X-ray emission spectroscopy (SXES) can be used as a powerful tool for the comprehensive analysis of the electronic and structural properties of lithium silicides Li x Si forming in LIB's anode upon Si lithiation. On the basis of density functional theory (DFT) and molecular dynamics (MD) simulations it is shown that coordination of Si atoms in Li x Si decreases with increase in Li concentration both for the crystalline and amorphous phases. In amorphous a-Li x Si alloys Si tends to cluster forming Si-Si covalent bonds even at the high lithium concentration. It is demonstrated that the Si-L 2,3 emission bands of the crystalline and amorphous Li x Si alloys show different spectral dependencies reflecting the process of disintegration of Si-Si network into Si clusters and chains of the different sizes upon Si lithiation. The Si-L 2,3 emission band of Li x Si alloys become narrower and shifts towards higher energies with an increase in Li concentration. The shape of the emission band depends on the relative contribution of the X-ray radiation from the Si atoms having different coordination. This feature of the Si-L 2,3 spectra of Li x Si alloys can be used for the detailed analysis of the Si lithiation process and LIB's anode structure identification.

The hypothesis of the huge optical nonlinearity of the crystalline TeO 3 , recently advanced on the basis of the quantummechanical simulations, is tested. Electronic band gaps of α-TeO 2 and β-TeO 3 crystals are determined by diffuse reflectance measurements. The DFT+U method is applied to calculate electronic band gap E g and the third-order nonlinear dielectric susceptibility χ (3) . The χ (3) (TeO 3 ) is about two times lower than the χ (3) (TeO 2 ) in spite of the fact that the E g (TeO 3 ) is narrower than E g (TeO 2 ). It is shown that this peculiarity is related to the 5s(Te) electronic states which are occupied in TeO 2 and are vacant in TeO 3 . This distinction is due to the specific electronic state related to the electron lone pairs localized on the Te(IV) atoms.