Multiscale Simulation of Irregular Shape Evolution during the Initial Stage of Zn Electrodeposition on a Negative Electrode Surface

Zn is a promising anode material for next-generation large-scale energy storage devices. However, irregular shape evolution on its surface during cycling causes electrode degradation. The shapes and crystal structures of the deposits naturally originate from the initial behaviors of the depositions. At the initial stage of deposition, a micro-protrusion initiates on the Zn electrode, leading to an irregular shape evolution. This study focuses on the initial steps of Zn deposition using a multiscale simulation comprising density functional theory (DFT) calculations and kinetic Monte Carlo (KMC) simulations. This simulation allows analyses of phenomena from the picometer to the nanometer scale to yield mechanistic insight into the shape evolution of the deposits with respect to the electronic state of a particular species. The DFT calculations indicate that the Zn adatom exhibits specific behavior during surface diffusion: faster flat surface diffusion on the (0001) surface and slower interlayer diffusion. The KMC simulations show an irregular shape evolution based on the surface diffusion behavior of Zn as follows: (i) a two-dimensional (2D) hexagonal nucleation of the (0001) surface occurs on the substrate; (ii) the adatoms accumulate on the first layer to form layer-by-layer structures; (iii) the layer-by-layer structure forms the mountain structure, where the top layer exhibits a small area; and (iv) the top layer results in the protrusion. Therefore, the (0001) surface and interlayer diffusion rates are significant in the irregular shape evolution.