Interrelationships among Grain Size, Surface Composition, Air Stability, and Interfacial Resistance of Al-Substituted Li7La3Zr2O12 Solid Electrolytes

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• 作者：Lei Cheng ; Cheng Hao Wu ; Angelique Jarry ; Wei Chen ; Yifan Ye ; Junfa Zhu ; Robert Kostecki ; Kristin Persson ; Jinghua Guo ; Miquel Salmeron ; Guoying Chen ; Marca Doeff
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：August 19, 2015
• 年：2015
• 卷：7
• 期：32
• 页码：17649-17655
• 全文大小：373K
• ISSN：1944-8252

文摘

The interfacial resistances of symmetrical lithium cells containing Al-substituted Li₇La₃Zr₂O₁₂ (LLZO) solid electrolytes are sensitive to their microstructures and histories of exposure to air. Air exposure of LLZO samples with large grain sizes (鈭?50 渭m) results in dramatically increased interfacial impedances in cells containing them, compared to those with pristine large-grained samples. In contrast, a much smaller difference is seen between cells with small-grained (鈭?0 渭m) pristine and air-exposed LLZO samples. A combination of soft X-ray absorption (sXAS) and Raman spectroscopy, with probing depths ranging from nanometer to micrometer scales, revealed that the small-grained LLZO pellets are more air-stable than large-grained ones, forming far less surface Li₂CO₃ under both short- and long-term exposure conditions. Surface sensitive X-ray photoelectron spectroscopy (XPS) indicates that the better chemical stability of the small-grained LLZO is related to differences in the distribution of Al and Li at sample surfaces. Density functional theory calculations show that LLZO can react via two different pathways to form Li₂CO₃. The first, more rapid, pathway involves a reaction with moisture in air to form LiOH, which subsequently absorbs CO₂ to form Li₂CO₃. The second, slower, pathway involves direct reaction with CO₂ and is favored when surface lithium contents are lower, as with the small-grained samples. These observations have important implications for the operation of solid-state lithium batteries containing LLZO because the results suggest that the interfacial impedances of these devices is critically dependent upon specific characteristics of the solid electrolyte and how it is prepared.