In Situ Liquid-Phase Transmission Electron Microscopy Investigation of Anode-Electrolyte Interface Processes in Zn-Ion Batteries.

Abstract

Aqueous zinc batteries (AZBs) are promising candidates for future energy storage systems due to their low cost and inherent safety that comes along with the nonflammable aqueous electrolyte. However, their practical application is hindered by safety concerns arising from zinc (Zn) metal dendrite formation. Understanding the nucleation and growth mechanisms of Zn dendrites is essential to mitigate short-circuit risks and improve the stability of rechargeable ZIBs. In this study, we present an in situ electrochemical liquid cell scanning transmission electron microscopy (EC-LC-STEM) investigation of Zn dendrite evolution, revealing a multistep growth pathway. Initially, Zn species exhibiting a distinct hexagonal morphology with a preferred crystallographic orientation nucleate at localized sites at the interface between the electrode and the electrolyte, forming stacked hexagonal platelets. These platelets serve as seeds, guiding the directional growth of subsequent Zn deposition. As ion reduction progresses, these early structures act as anchors for anisotropic growth, ultimately giving rise to branched dendritic architectures. This sequential development, from oriented hexagonal nuclei to extended branching, underscores the critical role of early stage Zn species in dictating dendrite morphology. These findings contribute to a deeper understanding of the morphological evolution of Zn dendrites and offer valuable guidance for the design of strategies aimed at suppressing unsafe Zn growth in aqueous and hybrid ZIB systems.