Zheng Hongkui, Xu Mingjie, He Kai
Department of Materials Science and Engineering, University of California, Irvine, CA, 92697, USA.
Irvine Materials Research Institute, University of California, Irvine, CA, 92697, USA.
Small. 2024 Feb;20(6):e2304799. doi: 10.1002/smll.202304799. Epub 2023 Oct 2.
Garnet-type Li La Zr O (LLZO) solid-state electrolytes hold great promise for the next-generation all-solid-state batteries. An in-depth understanding of the phase transformation during synthetic processes is required for better control of the crystallinity and improvement of the ionic conductivity of LLZO. Herein, the phase transformation pathways and the associated surface amorphization are comparatively investigated during the sol-gel and solid-state syntheses of LLZO using in situ heating transmission electron microscopy (TEM). The combined ex situ X-ray diffraction and in situ TEM techniques are used to reveal two distinct phase transformation pathways (precursors → La Zr O → LLZO and precursors → LLZO) and the subsequent layer-by-layer crystal growth of LLZO on the atomic scale. It is also demonstrated that the surface amorphization surrounding the LLZO crystals is sensitive to the postsynthesis cooling rate and significantly affects the ionic conductivity of pelletized LLZO. This work brings up a critical but often overlooked issue that may greatly exacerbate the Li-ion conductivity by undesired synthetic conditions, which can be leveraged to ameliorate the overall crystallinity to improve the electrochemical performance of LLZO. These findings also shed light on the significance of optimizing surface structure to ensure superior performance of Li-ion conductors.
石榴石型Li La Zr O（LLZO）固态电解质在下一代全固态电池方面具有巨大潜力。为了更好地控制LLZO的结晶度并提高其离子电导率，需要深入了解合成过程中的相变。在此，使用原位加热透射电子显微镜（TEM）对LLZO的溶胶-凝胶法和固态合成过程中的相变途径及相关表面非晶化进行了比较研究。结合非原位X射线衍射和原位TEM技术，揭示了两种不同的相变途径（前驱体→La Zr O→LLZO和前驱体→LLZO）以及随后LLZO在原子尺度上的逐层晶体生长。还证明了LLZO晶体周围的表面非晶化对合成后冷却速率敏感，并显著影响造粒LLZO的离子电导率。这项工作提出了一个关键但常被忽视的问题，即不期望的合成条件可能会极大地加剧锂离子传导率，而这可被用来改善整体结晶度以提高LLZO的电化学性能。这些发现也揭示了优化表面结构以确保锂离子导体卓越性能的重要性。
