Lithium Expulsion from the Solid-State Electrolyte Li6.4La3Zr1.4Ta0.6O12 by Controlled Electron Injection in a SEM

The garnet ionic conductor is one of the promising candidate electrolytes for all-solid-state secondary lithium batteries, thanks to its high lithium ion conductivity and good thermal and chemical stability. However, its microstructure is difficult to approach because it is very sensitive to the inquisitive electron beam. In this study based on a scanning electron microscope (SEM), we found that the electron beam expulses the lithium out of Li6.4La3Zr1.4Ta0.6O12 (LLZTO), and the expulsed zone expands to where a stationary beam could extend and penetrate. The expulsion of metallic lithium was confirmed by its oxidation reaction after nitrogen inflow into the SEM. This phenomenon may provide us an effective probe to peer into the conductive nature of this electrolyte. A frame-scan scheme is employed to measure the expulsion rate by controllable and more uniform incidence of electrons. Lithium accumulation processes are continuously recorded and classified into four modes by fitting its growth behaviors into a dynamic equation that is mainly related to the initial ion concentration and ion migration rate in the electrolyte. These results open a novel possibility of using the SEM probe to gain dynamic information on ion migration and lithium metal growth in solid materials.

石榴石型离子导体凭借其高锂离子电导率与优异的热、化学稳定性，成为全固态二次锂电池极具潜力的候选电解质之一。然而，该材料的微观结构难以表征，因其对入射电子束极为敏感。本研究基于扫描电子显微镜（Scanning Electron Microscope, SEM）开展，发现电子束会将Li₆.₄La₃Zr₁.₄Ta₀.₆O₁₂（LLZTO）中的锂脱出，且脱出区域会随静止电子束的辐照范围与穿透深度不断扩展。通过向SEM腔室通入氮气后观察到的氧化反应，证实了脱出产物为金属锂。该现象为探究该电解质的导电本质提供了一种有效的表征手段。本研究采用帧扫描方案，通过可控且更均匀的电子入射条件，实现对脱出速率的定量表征。研究持续记录锂的累积过程，并通过将其生长行为拟合至与电解质内初始离子浓度、离子迁移速率密切相关的动力学方程，将该过程划分为四种模式。本研究结果为利用SEM表征手段获取固体材料内部离子迁移与金属锂生长的动态信息开辟了全新的研究路径。