Understanding Li Metal Anode and Solid-Electrolyte-Interphase (SEI) with Cryogenic Electron Microscopy (cryo-EM) Yaolin Xu, Zdravko Kochovski and Yan Lu Department of Electrochemical Energy Storage (CE-AEES), Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), Hahn-Meitner-Platz 1, Berlin, Germany Understanding in detail the behaviour of Li deposition and SEI formation is crucial for the rational design of stable Li metal anodes, but has remained tremendously challenging due to the extremely high sensitivity of metallic Li. [1] To address this issue, cryogenic electron microscopy (cryo-EM) has in recent years emerged as a powerful tool for visualizing sensitive Li deposition and SEI on the nanoscale. In our study, to understand the morphological evolution of Li nucleation and deposition under various current densities, we performed multi-scale morphological characterization of Li deposits and the SEI using cryogenic transmission electron microscopy (cryo-TEM) combined with focused ion beam scanning electron microscopy (FIB/SEM). The Li deposits are found to be ball-shaped where the local charge density is low, while Li-whiskers appear where a high flux of Li-ions and electrons exists. Meanwhile, the Li-balls are concluded to be the origin of the Li-whiskers, and the ball-shaped deposits appear to be mostly amorphous while the Li-whiskers being highly crystalline. Moreover, the nanostructures and compositions of the SEI layer on Li balls and whiskers are different, with thin and LiF-dominated SEI on Li-balls and thick and organic-enriched one on Li-whiskers. The distinction in SEI is further correlated to the Li nucleation and growth behaviors of these two types of Li deposits. [2] Moreover, to decipher the Li deposition and SEI evolution processes under an operando polymerized SEI which resulted in an ultra-high Coulombic efficiency of 99.97% for Li plating/stripping, we used cryo-TEM and cryogenic electron tomography (cryo-ET), complemented with operando electrochemical atomic force microscopy (EC-AFM), which demonstrated the morphological evolution of Li deposits from large-sized and low-tortuosity spheres to columns, together with thinning of the operando polymerized SEI layer from ~100 nm to 7 nm and self-healing capability, leading to efficient Li stripping (i.e., with minimum “dead” Li) and non-continuous SEI formation. [3] These results provide new mechanistic understandings of Li deposition and SEI growth, which could guide the rational design Li metal anodes and interfaces toward stable operation. References 1. Y. Xu†, K. Dong†, Y. Jie†, et al., Promoting Mechanistic Understanding of Lithium Deposition and Solid-Electrolyte Interphase (SEI) Formation using Advanced Characterization and Simulation Methods: Recent Progress, Limitations, and Future Perspectives , Adv. Energy Mater. 2022, 2200398. 2. K. Dong†, Y. Xu†, et al., Unveiling the Lithium Nucleation and Growth Mechanism and the Correlation with the Solid Electrolyte Interface , ACS Energy Lett. 2021, 6, 1719−1728. 3. Y. Jie†, Y. Xu†, Y.Chen†, M. Xie†, et al., In-situ and Operando Polymerization Enabling Highly Reversible Lithium Metal Anode , Cell Rep. Phys. Sci. 2022, 3,101057.
P40
© The Author(s), 2023
Made with FlippingBook Learn more on our blog