First-Principles Study of Amorphous Al2O3 ALD Coating in Li-S Battery Electrode Design

The Li-S battery is exceptionally appealing as an alternative candidate beyond Li-ion battery technology due to its promising high specific energy capacity. However, several obstacles (e.g., polysulfides’ dissolution, shuttle effect, high volume expansion of cathode, etc.) remain and thus hinder the commercialization of the Li-S battery. To overcome these challenges, a fundamental study based on atomistic simulation could be very useful. In this work, a comprehensive investigation of the adsorption of electrolyte (solvent and salt) molecules, lithium sulfide, and polysulfide (Li2Sx with 2 ≤x≤ 8) molecules on the amorphous Al2O3 atomic layer deposition (ALD) surface was performed using first-principles density functional theory (DFT) calculations. The DFT results indicate that the amorphous Al2O3 ALD surface is selective in chemical adsorption towards lithium sulfide and polysulfide molecules compared to electrolytes. Based on this work, it suggests that the Al2O3 ALD is a promising coating material for Li-S battery electrodes to mitigate the shuttling problem of soluble polysulfides.

Nanoscale Soft Wetting Observed in Co/Sapphire during Pulsed Laser Irradiation

Liquid drops on deformable soft substrates exhibit quite complicated wetting behavior as compared to those on rigid solid substrates. We report on a soft wetting behavior of Co nanoparticles (NPs) on a sapphire substrate during pulsed laser-induced dewetting (PLID). Co NPs produced by PLID wetted the sapphire substrate with a contact angle near 70°, which is in contrast to typical dewetting behavior of metal thin films exhibiting contact angles greater than 90°. In addition, a nanoscale γ-Al2O3 wetting ridge about 15 nm in size and a thin amorphous Al2O3 interlayer were observed around and beneath the Co NP, respectively. The observed soft wetting behavior strongly indicates that the sapphire substrate became soft and deformable during PLID. Moreover, the soft wetting was augmented under PLID in air due to the formation of a CoO shell, resulting in a smaller contact angle near 30°.

Study on Process Optimization of Sprayable Powders and Deposition Performance of Amorphous Al2O3–YAG Coatings

In this study, the process optimization of sprayed powders and deposition performance for amorphous Al2O3–Y3Al5O12 (YAG) coatings was investigated. The solid-state reaction mechanism of the nano-sized Al2O3 and Y2O3 powders with eutectic molar ratio was studied by multiple step-by-step heating cycle calcination processes. The calcination process could be adjusted according the dominant control factors like chemical reaction rate or ion diffusion rate. Finally, the actual deposition performance of the calcined powders (Al2O3/YAG) was examined by atmospheric plasma spraying (APS). XRD, SEM and DTA were used to characterize the powders and the as-sprayed coatings. The results showed that the reaction of Al2O3–Y2O3 system is a high temperature solid reaction dominated by Al3+ diffusion, the initial reaction process was usually belong to chemical kinetic range, then the reaction will be transformed from chemical kinetic range to diffusion dynamic range with the temperature increasing. The process optimization of powders was very effective, and the deposition effect of coating was effective.