Study of the solid electrolyte interphase of Li-O2 battery electrolyte by analytical transmission electron microscopy

Investigation of solid electrolyte interphases (SEIs) on negative electrode surfaces is essential to improve the stable charge-discharge performance of rechargeable lithium-air batteries (Li-O2 batteries). In this study, a direct investigation of SEI films is conducted using analytical transmission electron microscopy (TEM). A thin Cu specimen is prefabricated for TEM observation and is utilised as a model substrate for SEI formation. The electrochemical cell constructed using dissolved oxygen in the electrolyte exhibits a greater electrochemical overpotential during the Li-metal deposition process than that constructed with a pristine electrolyte. This suggests that different electrochemical passivation features occur in each different electrochemical cell. TEM observation confirms that the surface film formed by O2 dissolute electrolyte is a polycrystalline Li2O film with a thickness of ~5 nm, whereas the film formed by the pristine electrolyte is organic-based, amorphous-like and 20–50 nm thick. The dissolved oxygen molecules are more easily reduced than the components of the electrolyte, leading to the formation of Li2O as a stable passivation SEI film, which is expected to exhibit good charge-discharge features during the operation of the Li-O2 battery.

Origins and importance of fine secondary α in slowly cooled Ti6Al4V

It has been known for sometime that slowly cooled Ti6Al4V (Ti64) contains only about 10vol% of β and that this β takes three different forms. Firstly, there are thin volumes of interfacial β, between the grains of α, which are clearly the remains of the β present at high temperatures left when α replaces the β present at high temperatures, by diffusion and boundary migration. Secondly, there are regions of roughly equiaxed β at triple points, but some of this β contains very fine secondary α, whereas the other grains are retained β. Analytical transmission electron microscopy has been used in an attempt to understand the origin of these two different types of equiaxed β grains. It has been found that grains, which are retained β contain about 20wt%V, but the β grains that contain secondary α originate from parent β grains that have only about 14wt%V. The origin and the significance of these observations will be discussed in the presentation.

Microstructure and Local Mechanical Properties of Skutterudites with Addition of Metallic Borides

Skutterudites are an important class of thermoelectric p- and n-type materials and they have already achieved fair efficiencies for the conversion of heat to electricity. Nevertheless researchers try to further enhance the figure of merit, ZT, by various ways. In this work we study microstructure and mechanical properties of two thermoelectric materials: an industrial n-type (Mm,Sm)yCo4Sb12 skutterudite and an industrial p-type DDyFe3CoSb12 skutterudite, both mixed with 1 wt.% of Ta0.8Zr0.2B. Thin lamellae were prepared from the compacted materials using a focused ion beam. Analytical transmission electron microscopy was used on lamellae to study details of microstructure. A fine dispersion of precipitates was found both at nanograin boundaries and in their interiors. Quasistatic and dynamic nanoindentation tests were carried out on planar polished sections in the range of applied loads from 0.01 to 10 mN. The results were complemented with quantitative modulus mapping of local mechanical properties with 10-nm resolution.