Nucleation of Pitting and Evolution of Stripping on Lithium-Metal Anodes.

The stripping reaction of lithium (Li) will greatly impact the cyclability and safety of Li-metal batteries. However, Li pits' nucleation and growth, the origin of uneven stripping, are still poorly understood. In this study, we analyze the nucleation mechanism of Li pits and their morphology evolution with a large population and electrode area (>0.45 cm2). We elucidate the dependence of the pit size and density on the current density and overpotential, which are aligned with classical nucleation theory. With a confocal laser scanning microscope, we reveal the preferential stripping on certain crystal grains and a new stripping mode between pure pitting and stripping without pitting. Descriptors like circularity and the aspect ratio (R) of the pit radius to depth are used to quantify the evolution of Li pits in three dimensions. As the pits grow, growth predominates along the through-planedirection, surpassing the expanding rate in the in-plane direction. After analyzing more than 1000 pits at each condition, we validate that the overpotential is inversely related to the pit radius and exponentially related to the rate of nucleation. With this established nucleation-overpotential relationship, we can better understand and predict the evolution of the surface area and roughness of Li electrodes under different stripping conditions. The knowledge and methodology developed in this work will significantly benefit Li-metal batteries' charging/discharging profile design and the assessment of large-scale Li-metal foils.

Solidification-Controlled Compartmentalization of Bismuth-Tin Colloidal Particles.

Nucleation and growth are the main steps of microstructure formation. Nucleation occurs stochastically in a bulk material but can be controlled by introducing or removing catalytic sites, or creating local gradients. Such manipulations can already be implemented to bulk materials at a high level of sophistication but are still challenging on micrometer or smaller scales. Here, we explore the potential to transfer this vast knowledge in classical metallurgy to the fabrication of colloidal particles and report strategies to control phase distribution within a particle by adjusting its solidification conditions. Benefiting from the core-shell structure of liquid metals and the constrained volume of particles, we demonstrate that the same alloy particle can be transformed into a lamellar, composite, Janus, or striped particle by the felicitous choice of the phase separation process pathway. This methodology offers an unprecedented opportunity for the scalable production of compartmentalized particles in high yields that are currently limited to inherently unscalable methods.