Unraveling the Mechanisms of Lithium Metal Plating/Stripping via In Situ/Operando Analytical Techniques

Lithium, the lightest metal with the lowest standard reduction potential, has been long considered as the ultimate anode material for next-generation high-energy-density batteries. However, an unexpected Li dendrite formation, which causes poor reversibility of electrochemical reactions and safety concerns, is a major problem that has to be solved for the commercialization of Li metal anodes. For the implementation of stable Li metal anodes, complete understanding on the dendritic Li formation and its dissolution is essential for electrode material design, which requires the development of advanced characterization techniques. Specifically, compared to an ex situ characterization as a postmortem analysis, in situ/operando characterizations allow dynamic structural and chemical evolution to be directly observed in a realistic battery cell, which helps unravel the complex reactions and degradation mechanisms in Li metal anodes. Here, recent progress in the understanding of electrochemical behavior in Li metal anodes upon deposition and dissolution, verified by the in situ/operando analytical techniques using light, electron, X-ray, neutron, and magnetism-based characterizations, is covered. This progress report provides a fundamental understanding of Li deposition and dissolution mechanisms and highlights the critical role of in situ/operando analyses in developing stable Li metal anodes.