Uncovering the Dynamics\nof Li–Au Alloying and\nLi Nucleation at the Au/LiPON Interface with In Situ <i>Z</i> Contrast and Surface Roughness Contrast Imaging via Scanning Electron\nMicroscopy

Controlling the nucleation, growth, and dissolution of\nLi is crucial\nfor the high cycling stability in rechargeable Li metal batteries.\nThe overpotential for Li nucleation (η<sub>nc</sub>) on Li alloys\nsuch as Li–Au is generally lower than that on metal current\ncollectors (CCs) with very limited Li solubility like Cu. However,\nthe alloying process of CC and its impact on the Li nucleation kinetics\nremain unclear. Herein, we experimentally investigate the Li nucleation\nmechanism on Li–Au alloys using scanning electron microscopy\nwith multiple detectors to distinguish the atomic number and topography\ncontrast. Nonequilibrium processes near the Au CC film/lithium phosphorus\noxynitride (LiPON) glass electrolyte interface were observed. Local\ndissolution of Li occurs concurrently with the Li plating process.\nThis phenomenon indicates that Li nucleates as a metastable phase\nin Li–Au alloy CC films during Li plating due to the substantially\nlower interfacial energy of Li with the alloy phase. This low interfacial\nenergy also leads to a low η<sub>nc</sub>. Moreover, the local\nLi redissolution process results in a nonrandom spatial distribution\nof Li growth sites. Consequently, the alloy layer acts as a buffer,\nfacilitating a more uniform distribution of the reaction sites.