Unveiling the mechanism of lithium dendrite infiltration into solid state electrolyte through the coupling of electrochemical and in-situ optical characterization

Garnet type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO) is a promising choice for solid-state Lithium (Li) batteries due to its high ion conductivity and high stability to Li metal. However, LLZO based Li batteries also suffer from the problem of Li dendrite infiltration, in which the growth mode of Li dendrite is indefinite. To explore the scientific problem, electrochemical characterizations combined with in-situ optical observation are employed to reveal the origin of Li dendrite, the relationship between Li dendrite evolution and electrochemical properties. It shows that poor interface contact leads a high polarization voltage at Li dissolution step, and the upcoming Li deposition step is likely to form Li dendrite and cause short circuit. The electric field distribution simulation of the Li/LLZO interface also demonstrates that the deterioration of interface contact can lead to uneven electric field distribution, which may trigger Li dendrite growth during the Li deposition process. In-situ optical observation using a transparent LLZO electrolyte is carried out and confirms the above results directly. Meanwhile, the connection between the behavior of Li dendrite and the voltage profile is established that high polarization voltage before the deposition process is an indicator of Li dendrite formation, which is expected to provide guidance for the predicting work of short circuit in advance. These findings can promote a thorough understanding for the failure mechanism of solid-state cells caused by Li dendrite.