Effect of mechanical treatment on the distribution of valence electrons and characteristics of nanocomposite (SiO2)x(Al2O3)1-x (x = 0.8, x = 0.7) electrodes in lithium power sources

Abstract

Ultra-soft X-ray emission spectroscopy was used to study the distribution of Op-, Sisd- and Alsd- valence electrons in (SiO2)x(Al2O3)1-x (x = 0.8, x = 0.7) powder mixtures after mechanical treatment. An increase in atomic charges has been measured and can be explained by the transfer of electrons from Si/Al to O atoms in split Opπ-binding states and the formation of the weak long (OO)π bonds between the surface atoms of the contacted powder nanoparticles. Scanning and transmission electron microscopy images show an enhanced agglomeration of the nanoparticles of both SiO2 and Al2O3 oxides, but no changes in the crystalline parameters have been measured using X-ray diffraction. An increase in charge capacities of lithium ion power sources with 0.8SiO2–0.2Al2O3 electrode has been observed during cycling. At the same time, a decrease of the charge capacities with the 0.7SiO2–0.3Al2O3 electrode has been measured. The results are discussed in terms of an increase in the binding energy of electrons in the Op-states, which prevents the recombination and irreversible reactions of lithium with electrode atoms. Otherwise, due to cycling, electron population increase of in non-binding states near the valence band top contributes to the recombination ability of Li+ ions and leads to a decrease in the charge capacity.