Local surface crystal structure fluctuation on Li, Na and Mg metal anodes

Abstract

Dendrite formation occurs on Li, Na, and Mg metal anodes in rechargeable batteries, and is a safety challenge, as well as a limiting factor for increasing energy- and power density. However, the behaviour of the dendrites differs depending on the anode material. In this study, we investigate the local bulk and surface crystal structure of Li, Na, and Mg surfaces to shed light on how differences in the morphology and structure of the anode surface and its metal deposits can explain differences in dendrite formation on Li, Na, and Mg anodes. The local bulk- and surface structure are found using molecular dynamics simulations in combination with the surface adaptive common neighbour analysis, and indicate that Li and Na surfaces are more prone to surface instabilities and formation of protrusions than Mg surfaces, which remain flat and hexagonal close-packed even near room temperature. Additionally, the equilibrium shapes of the Mg deposits obtained from density functional theory assume more flat and hexagonal shapes than the Li and Na deposits. Together, these results shed light on atomic mechanisms that may contribute to the different propensities of Li, Na, and Mg metal anodes to form dendrites.