Lithium Metal Anodes: Operando Observation of Nucleation, Dendrite Growth, and Dead Lithium Formation

Abstract

Lithium (Li) metal anodes have experienced a resurgence of research in recent years, which has been fueled by advances in electrolyte chemistry (both solid and liquid), interfacial engineering, and rational design of electrode architectures1. This has enabled Coulombic efficiency values to push above 99.5%, and cycle life to extend into relevant ranges for transportation applications2. However, while performance metrics are beginning to approach relevant values for consideration of their use in electric vehicles, several fundamental questions remain on how Li metal anodes dynamically evolve during cycling, especially at high current densities. Towards this goal, there is a continued need for new methods to understand the evolving morphology from nucleation, to growth, to irreversible capacity loss.In this talk, operando optical microscopy will be discussed as an enabling platform to study the coupled chemical, electrochemical, mechanical, and morphological evolution of Li metal during plating and stripping. By time synchronization of the morphological evolution of Li metal anodes with electrochemical signatures during cycling, significant insights can be obtained into the mechanistic origins of poor performance3-4. Both cross-sectional and plan-view perspectives on the electrode surface will be described, which allow for a full 3-dimensional understanding of nucleation and growth processes. Video imaging of Li metal propagation in both liquid and solid electrolytes will be presented, and the critical role of mechanical stress evolution in Li metal morphology will be described5-6. A focus will be on the formation of “dead Li”, which form as a result of electronic isolation of metallic Li from the electrode surface3. Finally, strategies to modify surface chemistry and electrode geometry will be described, providing design rules for interfacial engineering of optimized electrodes2.1) Wood, K. N.; Noked, M.; Dasgupta, N. P. Lithium Metal Anodes: Toward an Improved Understanding of Coupled Morphological, Electrochemical, and Mechanical Behavior. ACS Energy Lett. 2017, 2 (3), 664–672.2) Chen, K.-H.; Sanchez, A. J.; Kazyak, E.; Davis, A. L.; Dasgupta, N. P. Synergistic Effect of 3D Current Collectors and ALD Surface Modification for High Coulombic Efficiency Lithium Metal Anodes. Adv. Energy Mater. 2019, 9 (4), 1802534.3) Wood, K. N.; Kazyak, E.; Chadwick, A. F.; Chen, K.-H.; Zhang, J.-G.; Thornton, K.; Dasgupta, N. P. Dendrites and Pits: Untangling the Complex Behavior of Lithium Metal Anodes through Operando Video Microscopy. ACS Cent. Sci. 2016, 2 (11) 790-801.4) Chen, K.-H.; Wood, K. N.; Kazyak, E.; LePage, W. S.; Davis, A. L.; Sanchez, A. J.; Dasgupta, N. P. Dead Lithium: Mass Transport Effects on Voltage, Capacity, and Failure of Lithium Metal Anodes. J. Mater. Chem. A 2017, 5 (23), 11671–11681.5) LePage, W. S.; Chen, Y.; Kazyak, E.; Chen, K.-H.; Sanchez, A. J.; Poli, A.; Arruda, E. M.; Thouless, M. D.; Dasgupta, N. P. Lithium Mechanics: Roles of Strain Rate and Temperature and Implications for Lithium Metal Batteries. J. Electrochem. Soc. 2019, 166 (2), A89–A97.6) Gupta, A.; Kazyak, E.; Craig, N.; Christensen, J.; Dasgupta, N. P.; Sakamoto, J. Evaluating the Effects of Temperature and Pressure on Li/PEO-LiTFSI Interfacial Stability and Kinetics. J. Electrochem. Soc. 2018, 165 (11), A2801–A2806.