Investigation of Failure Mechanisms in Lithium Metal Solid-State Batteries Based on In Situ Electrochemical Impedance Spectroscopy

With the growing global demand for sustainable energy and high-performance mobile devices, lithium metal solid-state batteries (LMBs) have emerged as a research hotspot in the field of energy storage due to their exceptional high energy density and significant safety advantages. However, the growth of lithium dendrites and their penetration through the solid electrolyte remain key issues leading to battery short-circuiting and failure. To date, there has been a lack of effective in situ research methods to reveal the failure mechanisms, which has severely restricted the commercialization of LMBs. This study innovatively employs in situ electrochemical impedance spectroscopy (EIS) to investigate lithium plating behavior in symmetric cells during critical current density (CCD) tests under room temperature and elevated temperature conditions. By analyzing characteristic signals at 1 MHz, this study presents the in situ impedance changes at the grain boundaries and interfaces of the battery, revealing that lithium plating is a dynamic reduction-oxidation process. We summarize two modes of lithium plating: one involves lithium metal deposition at the interface due to local current density inhomogeneity; the other involves lithium metal deposition at grain boundaries far from the electrode due to concentration gradient differences. The study further reveals that lithium plating at grain boundaries is the primary cause of battery failure. This research highlights the unique advantages of in situ EIS in the field of solid-state battery research and its applicability to various material systems. Moreover, the proposed lithium plating mechanism provides a theoretical basis for optimizing battery design and enhancing battery safety, thereby facilitating the realization of high-energy-density solid-state batteries.