Vitaliy Yurkiv

Facet-Dependent Thermal Instability in LiCoO2

Thermal runaways triggered by the oxygen release from oxide cathode materials pose a major safety concern for widespread application of lithium ion batteries. Utilizing in situ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) at high temperatures, we show that oxygen release from LixCoO2 cathode crystals is occurring at the surface of particles. We correlated this local oxygen evolution from the LixCoO2 structure with local phase transitions spanning from layered to spinel and then to rock salt structure upon exposure to elevated temperatures. Ab initio molecular dynamics simulations (AIMD) results show that oxygen release is highly dependent on LixCoO2 facet orientation. While the [001] facets are stable at 300 °C, oxygen release is observed from the [012] and [104] facets, where under-coordinated oxygen atoms from the delithiated structures can combine and eventually evolve as O2. The novel understanding that emerges from the present study provides in-depth insights into the thermal runaway mechanism of Li-ion batteries and can assist the design and fabrication of cathode crystals with the most thermally stable facets.

Long-Range Self-Assembly via the Mutual Lorentz Force of Plasmon Radiation

Long-range interactions often proceed as a sequence of hopping through intermediate, statistically favored events. Here, we demonstrate predictable mechanical dynamics of particles that arise from the Lorentz force between plasmons. Even if the radiation is weak, the nonconservative Lorentz force produces stable locations perpendicular to the plasmon oscillation; over time, distinct patterns emerge. Experimentally, linearly polarized light illumination leads to the formation of 80 nm diameter Au nanoparticle chains, perpendicularly aligned, with lengths that are orders of magnitude greater than their plasmon near-field interaction. There is a critical intensity threshold and optimal concentration for observing self-assembly.

Modeling of Droplet Impact onto Polarized and Nonpolarized Dielectric Surfaces

This paper is concerned with simulation of the droplet impact on a dielectric surface, referred to as the dynamic electrowetting-on-dielectric (DEWOD). In particular, we seek to shed more light on the fundamental processes occurring during the impact of an electrically conducting droplet onto a dielectric surface with and without an applied voltage. The liquid in the droplet is an ionic conductor (a leaky dielectric). This work employs an approach based on Cahn-Hilliard-Navier-Stokes (CHNS) modeling. The simulations are validated by predicting the equilibrium contact angle, droplet oscillations, and charge density estimation. Then, four cases of droplet impact are studied, namely, the impact onto a surface with no voltage applied and the impacts onto the surfaces with 2, 4, and 6 kV applied. The modeling results of water droplet impact allow for direct comparison with the experimental results reported by Lee et al. [ Langmuir 2013, 29, 7758]. The results reveal the electric field, the body forces acting on the droplet, the velocity and pressure fields inside and outside the droplet, as well as the free charge density and the electric energy density. The model predicts the droplet shape evolution (e.g., the spreading distance over the surface and the rebound height) under different conditions that are consistent with the experimental observations. Thus, our findings provide new qualitative and quantitative insights into the droplet manipulation that can be used in novel applications of the DEWOD phenomenon.