Early Stage Li Plating by Liquid Phase and Cryogenic Transmission Electron Microscopy

Abstract

Li metal anodes are among the most promising options for next-generation batteries, exhibiting the highest theoretical capacity. However, irregular Li electrodeposition, which raises safety concerns, is a major obstacle in practical applications. Therefore, a fundamental understanding of the beginning phases of Li plating, such as nucleation and early growth, which have a decisive influence on the dendritic growth of Li, is essential. In this study, we investigated the early stage of Li plating at the single-particle level and its correlation with the solid-electrolyte interphase (SEI) using in situ liquid phase transmission electron microscopy (TEM) and cryogenic TEM. We observed contrasting nucleation dynamics and particle growth patterns in two electrolytes (1 M LiPF 6 in ethylene carbonate/diethyl carbonate and 1 M LiTFSI in 1,3dioxolane/dimethoxy ethane), which originate from different chemical and physical properties of the SEIs. Based on our findings, we propose a mechanism of nucleation and initial growth of Li dictated by the SEI.

Getting the Most Out of Fluorogenic Probes: Challenges and Opportunities in Using Single-Molecule Fluorescence to Image Electro- and Photocatalysis

“…While STM is well suited for imaging single-crystal surfaces, transmission electron microscopy (TEM) is better matched for imaging nanoscale catalyst particles (e.g., spherical nanoparticles, nanorods, and nanowires). The development of in situ holders for TEM in which gas and liquids can be introduced has enabled atomic-level visualization of the changes in nanoscale catalysts after reactive chemical species (e.g., H 2 , O 2 , or CO) are introduced into the cell. − In-situ holders designed for introducing gases are particularly useful for studying structural changes at elevated temperatures (e.g., 150 to 800 °C) during vapor-phase reactions such as methane oxidation, CO oxidation, − and other reactions. , In-situ liquid-cell holders with the ability to apply an electrical bias can be used to monitor morphological changes during electrochemical processes such as lithiation/delithiation, metal dendrite formation, − and, more recently, electrochemical reactions including water oxidation and oxygen reduction. , Changes in the surface structure of photocatalyst particles, such as titanium dioxide (TiO 2 ), under UV irradiation and in the presence of H 2 O have also been imaged. , While transmission electron microscopes can be coupled with instrumentation for detecting reaction products through mass spectrometry (MS) or electron energy loss spectroscopy (EELS), ,,− there is currently no way to correlate a specific region of the catalyst with the number of turnovers at that site nor how the observed structural changes affect its relative activity. So far, mapping the relative reactivity of different regions has been limited to reactions that produce gaseous products (e.g., water splitting to produce H 2 and O 2 gas) by imaging the formation of gas bubbles in liquid cells. ,, However, the gas bubbles are significantly larger (i.e., tens to hundreds of nanometers) than the reaction sites producing the bubbles.…”

Additive-Driven Nanoscale Architecture of Solid Electrolyte Interphase Revealed by Cryogenic Transmission Electron Microscopy

“…For example, nonuniformity in SEI induces localized Li ion flux on the SEI surface, resulting in sequential heterogeneous Li nucleation. 9,10 Different compositions in SEI lead to different morphologies of Li, such as Li balls and Li whiskers. 11 Moreover, SEI structures (mosaic, multilayer, etc.)…”

“…Structures of SEI determine Li growth, owing to the fact that Li ions must pass through the SEI layer before undergoing reduction on the Li metal surface. For example, nonuniformity in SEI induces localized Li ion flux on the SEI surface, resulting in sequential heterogeneous Li nucleation. , Different compositions in SEI lead to different morphologies of Li, such as Li balls and Li whiskers . Moreover, SEI structures (mosaic, multilayer, etc.)…”

In Situ TEM Studies on Electrochemical Mechanisms of Rechargeable Ion Battery Cathodes

“…For example, He et al tracked the catalytic behavior of nanoscale Cu in CO 2 atmosphere by in situ gas TEM holder, via which the working/failure mechanisms of Cu for CO 2 reduction were clearly disclosed at the microscopic level. [ 9 ] In addition, a variety of TEM techniques are widely used in solid‐state battery field, among which cryo‐TEM and in situ TEM have shown special roles in revealing the dendrite growth problem of Li metal anode [ 10 ] and understanding the mechanism of solid–solid interface, [ 11 ] respectively.…”