Leonardo Shoji Aota

The development of sustainable transportation and communication systems requires an increase in both energy density and capacity retention of Li‐batteries. Using substrates forming a solid solution with body‐centered cubic Li enhances the cycle stability of anode‐less batteries. However, it remains unclear how the substrate microstructure affects the lithiation behavior. Here, a correlative, near‐atomic scale probing approach is deployed through combined ion‐ and electron‐microscopy to examine the distribution of Li in Li‐Ag diffusion couples as model system mimicking high current densities. It is revealed that Li regions with over 93.8% at.% nucleate within Ag at random high‐angle grain boundaries, whereas grain interiors are not lithiated. The role of kinetics and mechanical constraint from the microstructure over equilibrium thermodynamics in dictating the lithiation process is evidenced. The findings suggest that grain size and grain boundary character are critical to enhance the electrochemical performance of interlayers/electrodes, particularly for improving lithiation kinetics and hence reducing dendrite formation.

The early stages of corrosion occurring at liquid‐solid interfaces control the evolution of the material's degradation process, yet due to their transient state, their analysis remains a formidable challenge. Here corrosion tests are performed on a MgCa alloy, a candidate material for biodegradable implants using pure water as a model system. The corrosion reaction is suspended by plunge freezing into liquid nitrogen. The evolution of the early‐stage corrosion process on the nanoscale by correlating cryo‐atom probe tomography (APT) with transmission‐electron microscopy (TEM) and spectroscopy, is studied. The outward growth of Mg hydroxide Mg(OH)₂ and the inward growth of an intermediate corrosion layer consisting of hydrloxides of different compositions, mostly monohydroxide Mg(OH) instead of the expected MgO layer, are observed. In addition, Ca partitions to these newly formed hydroxides and oxides. Density‐functional theory calculations suggest a domain of stability for this previously experimental unreported Mg(OH) phase. This new approach and these new findings advance the understanding of the early stages of magnesium corrosion, and in general reactions and processes at liquid‐solid interfaces, which can further facilitate the development of corrosion‐resistant materials or better control of the biodegradation rate of future implants.

Atom probe tomography requires needle-shaped specimens with a diameter typically below 100 nm, making them both very fragile and reactive, and defects (notches at grain boundaries or precipitates) are known to affect the yield and data quality. The use of a conformal coating directly on the sharpened specimen has been proposed to increase yield and reduce background. However, to date, these coatings have been applied ex situ and mostly are not uniform. Here, we report on the controlled focused-ion beam in situ deposition of a thin metal film on specimens immediately after specimen preparation. Different metallic targets e.g. Cr were attached to a micromanipulator via a conventional lift-out method and sputtered using Ga or Xe ions. We showcase the many advantages of coating specimens from metallic to nonmetallic materials. We have identified an increase in data quality and yield, an improvement of the mass resolution, as well as an increase in the effective field-of-view. This wider field-of-view enables visualization of the entire original specimen, allowing to detect the complete surface oxide layer around the specimen. The ease of implementation of the approach makes it very attractive for generalizing its use across a very wide range of atom probe analyses.