Preparation of transparent LLZTO electrolyte and its application in the observation of Li dendrite

The application of solid-state electrolytes endows the distinctive features of high safety and high energy density for lithium (Li) metal batteries. Among all kinds of solid-state electrolytes, garnet-type Li₇La₃Zr₂O₁₂ (LLZO) with high Young's modulus is a promising candidate. Nevertheless, Li metal can still grow inside LLZO and lead to short circuit. But it is difficult to determine the failure mechanism caused by Li dendrite due to the opacity of the common LLZO. Herein, a transparent Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) electrolyte is fabricated for the observation of Li growth inside the electrolyte directly. The factor that influences the transparency of LLZTO is investigated thoroughly, which is crucial for studying the behavior of Li metal during the plating process inside LLZTO. Results demonstrate that the amount of residual Li-containing compound at grain boundaries is the dominant factor influencing the transparency of LLZTO. The formation of Li filament and its growth process inside transparent LLZTO are also observed directly.