Operando Visualization of Li Metal Anodes—From Liquid to Solid Electrolytes

In recent years, there has been an explosion of research into Li metal anodes for high-energy-density batteries. However, despite tremendous progress in the field, the reversible plating and stripping of Li has been hindered by the complex interplay between electrode morphology, surface chemistry, and mechanics. This has led to many empirical observations of improved performance, but our ability to rationally design solutions to solve the challenges of reversibility remain limited by our fundamental understanding of the complex electrodeposition and dissolution processes involved [1]. Moreover, the emergence of solid-state batteries has created new opportunities to enable Li metal anodes, but the unique chemo-mechanical coupling at solid-solid interfaces also brings new challenges for Li metal anodes.<br/><br/>To address these challenges, <i>in situ/operando</i> analyses are of paramount importance to the community. However, given the dynamic nature of Li plating and stripping, challenges arise with respect to tradeoffs in spatial and temporal resolution. To address these challenges, we have recently integrated our optical visualization cells with a digital microscope capable of focus variation microscopy. This enables 3-D visualization of the electrode morphology with high temporal resolution, allowing for video capture of Li plating and stripping [2].<br/><br/>In this talk, I will discuss the application of <i>operando</i> 3-D microscopy for visualization of Li metal anodes using both liquid and solid-state electrolytes. In the case of Li metal anodes, we observe significant anisotropy in the geometric shape of individual pits during stripping [2]. The nucleation density and anisotropy are shown to be strongly influenced by the surface microstructure and underlying crystallographic texture of the Li metal surface. As a results, pits can exhibit strong faceting, which influences the nature of nucleation at pit edges in subsequent cycles [3].<br/><br/>The dynamic morphological evolution of Li metal anodes for solid-state batteries will also be demonstrated using 3-D microscopy. This enables visualization of nucleation and growth in anode-free architectures, where the Li metal anode is formed <i>in situ</i> at a solid electrolyte/current collector interface [4]. The similarities and differences between liquid and solid systems will be discussed in the context of electro-chemo-mechanical coupling, pointing towards new opportunities to enable reversible plating and stripping.<br/><br/>References<br/>[1] A. J. Sanchez, N. P. Dasgupta, <i>J. Am. Chem. Soc.</i> <b>146</b>, 4282 (2024)<br/>[2] A. J. Sanchez, E. Kazyak, Y. Chen, J. Lasso, N. P. Dasgupta, <i>J. Mater Chem. A. </i><b>9</b>, 21013 (2021).<br/>[3] A. J. Sanchez, E. Kazyak, Y. Chen, K.-H. Chen, E. R. Pattison, N. P. Dasgupta<b>, </b><i>ACS Energy Lett.</i> <b>5</b>, 994 (2020).<br/>[4] E. Kazyak, E., M. Wang, K. Lee, K, S. Yadavalli, A. J. Sanchez, M. D. Thouless, J. Sakamoto, N. P. Dasgupta, <i>Matter</i> <b>5</b>, 3912 (2022).