Otoyama Misae, Suyama Motoshi, Hotehama Chie, Kowada Hiroe, Takeda Yoshihiro, Ito Koichiro, Sakuda Atsushi, Tatsumisago Masahiro, Hayashi Akitoshi
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan.
Research Institute of Electrochemical Energy, Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan.
ACS Appl Mater Interfaces. 2021 Feb 3;13(4):5000-5007. doi: 10.1021/acsami.0c18314. Epub 2021 Jan 20.
The application of lithium metal as a negative electrode in all-solid-state batteries shows promise for optimizing battery safety and energy density. However, further development relies on a detailed understanding of the chemo-mechanical issues at the interface between the lithium metal and solid electrolyte (SE). In this study, crack formation inside the sulfide SE (LiPS: LPS) layers during battery operation was visualized using X-ray computed tomography (X-ray CT). Moreover, the degradation mechanism that causes short-circuiting was proposed based on a combination of the X-ray CT results and scanning electron microscopy images after short-circuiting. The primary cause of short-circuiting was a chemical reaction in which LPS was reduced at the lithium interface. The LPS expanded during decomposition, thereby forming small cracks. Lithium penetrated the small cracks to form new interfaces with fresh LPS on the interior of the LPS layers. This combination of reduction-expansion-cracking of LPS was repeated at these new interfaces. Lithium clusters eventually formed, thereby generating large cracks due to stress concentration. Lithium penetrated these large cracks easily, finally causing short-circuiting. Therefore, preventing the reduction reaction at the interface between the SE and lithium metal is effective in suppressing degradation. In fact, LPS-LiI electrolytes, which are highly stable to reduction, were demonstrated to prevent the repeated degradation mechanism. These findings will promote all-solid-state lithium-metal battery development by providing valuable insight into the design of the interface between SEs and lithium, where the selection of a suitable SE is vital.
锂金属作为负极应用于全固态电池中，有望优化电池安全性和能量密度。然而，进一步的发展依赖于对锂金属与固体电解质（SE）界面处化学机械问题的详细理解。在本研究中，利用X射线计算机断层扫描（X射线CT）可视化了电池运行期间硫化物SE（LiPS：LPS）层内部的裂纹形成。此外，基于X射线CT结果和短路后扫描电子显微镜图像的结合，提出了导致短路的降解机制。短路的主要原因是LPS在锂界面处发生还原的化学反应。LPS在分解过程中膨胀，从而形成小裂纹。锂穿透小裂纹，在LPS层内部与新鲜的LPS形成新的界面。LPS的这种还原 - 膨胀 - 开裂组合在这些新界面处重复发生。锂簇最终形成，由于应力集中产生大裂纹。锂很容易穿透这些大裂纹，最终导致短路。因此，防止SE与锂金属界面处的还原反应对于抑制降解是有效的。事实上，对还原高度稳定的LPS - LiI电解质被证明可以防止重复的降解机制。这些发现将通过为SE与锂之间界面的设计提供有价值的见解来促进全固态锂金属电池的发展，其中选择合适的SE至关重要。
