The reversible cycling of Li metal anodes is severely limited by poor cycle life and safety concerns. Dendrite growth has been linked to the poor performance of Li metal, but a comprehensive understanding of the mechanistic origins and dynamic evolution of Li metal morphology during electrodeposition and stripping is missing. Herein, a multifunctional operando visualization platform that synchronizes optical recordings with cycling electrochemistry is used to study nucleation on Li metal and dendrite reversibility. This platform was initially used to understand the origins of the “peaking” behavior exhibited in the voltage traces of Li symmetric cells [1-3]. However, by limiting the viewing angle to a cross-sectional perspective, the impact of electrode surface variations, including microstructure, flaws, and chemical inhomogeneities cannot be fully accounted for. To address this, a plan-view optical visualization cell was designed that maintains a highly uniform current distribution along the electrode surface. The top-down view provided by the updated cell is better suited to provide quantitative measurements of nucleation on Li metal and identify links between nucleation and microstructure.
Utilizing this new cell, we are able to: 1) Quantitatively identify the spatial distribution of “hot spots” for both nucleation of both dendrites and pits; 2) Detail how these hot spots evolve during cycling; 3) Quantify dendrite and pit areal nucleation density as a function of current density; 4) Provide an understanding of why surface uniformity increases after the first cycle; 5) Elucidate the substantial impact that pits have on Li metal cycling; 6) Explore the dependency between dendrite size and reversibility; and 7) Explore the mechanisms that lead to the formation of dead Li. The knowledge from this study can be used to inform rational design of Li metal surface treatments and architectures to improve the reversibility and cycle life.
1. K. N. Wood, E. Kazyak, A. F. Chadwick, K. H. Chen, J. G. Zhang, K. Thornton, N. P. Dasgupta, ACS Cent. Sci. 2, 790 (2016)
2. K. N. Wood, M. Noked, N. P. Dasgupta, ACS Energy Lett. 2, 664 (2017)
3. K.-H. Chen, K. N. Wood, E. Kazyak, W. S. LePage, A. L. Davis, A. J. Sanchez, N. P. Dasgupta, J. Mater. Chem. A 5, 11671 (2017)
