Wang Wei-Wei, Gu Yu, Yan Hao, Li Kai-Xuan, Chen Zhao-Bin, Wu Qi-Hui, Kranz Christine, Yan Jia-Wei, Mao Bing-Wei
State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.
College of Mechanical and Energy Engineering, Jimei University, Xiamen, 361021, China.
Faraday Discuss. 2022 Apr 5;233(0):190-205. doi: 10.1039/d1fd00043h.
Copper is the most widely used substrate for Li deposition and dissolution in lithium metal anodes, which is complicated by the formation of solid electrolyte interphases (SEIs), whose physical and chemical properties can affect Li deposition and dissolution significantly. However, initial Li nucleation and growth on bare Cu creates Li nuclei that only partially cover the Cu surface so that SEI formation could proceed not only on Li nuclei but also on the bare region of the Cu surface with different kinetics, which may affect the follow-up processes distinctively. In this paper, we employ atomic force microscopy (AFM), together with X-ray photoelectron spectroscopy (XPS), to investigate how SEIs formed on a Cu surface, without Li participation, and on the surface of growing Li nuclei, with Li participation, affect the components and structures of the SEIs, and how the formation sequence of the two kinds of SEIs, along with Li deposition, affect subsequent dissolution and re-deposition processes in a pyrrolidinium-based ionic liquid electrolyte containing a small amount of water. Nanoscale AFM observations show that sphere-like Li deposits may have differently conditioned SEI-shells, depending on whether Li nucleation is preceded by the formation of the SEI on Cu. Models of integrated-SEI shells and segmented-SEI shells are proposed to describe SEI shells formed on Li nuclei and SEI shells sequentially formed on Cu and then on Li nuclei, respectively. "Top-dissolution" is observed for both types of shelled Li deposits, but the integrated-SEI shells only show wrinkles, which can be recovered upon Li re-deposition, while the segmented-SEI shells are apparently top-opened due to mechanical stresses introduced at the junctions of the top regions and become "dead" SEIs, which forces subsequent Li nucleation and growth in the interstice of the dead SEIs. Our work provides insights into the impact mechanism of SEIs on the initial stage Li deposition and dissolution on foreign substrates, revealing that SEIs could be more influential on Li dissolution and that the spatial integration of SEI shells on Li deposits is important to improving the reversibility of deposition and dissolution cycling.
铜是锂金属负极中锂沉积和溶解最广泛使用的基底，而固体电解质界面（SEI）的形成使这一过程变得复杂，其物理和化学性质会显著影响锂的沉积和溶解。然而，裸铜表面上的初始锂成核和生长会产生仅部分覆盖铜表面的锂核，因此SEI的形成不仅可以在锂核上进行，还可以在铜表面的裸区域以不同的动力学进行，这可能会对后续过程产生显著影响。在本文中，我们采用原子力显微镜（AFM）以及X射线光电子能谱（XPS），来研究在无锂参与情况下铜表面形成的SEI以及在有锂参与情况下生长的锂核表面形成的SEI如何影响SEI的成分和结构，以及这两种SEI的形成顺序与锂沉积一起如何影响含少量水的吡咯烷鎓基离子液体电解质中的后续溶解和再沉积过程。纳米级AFM观察表明，球状锂沉积物可能具有不同条件的SEI壳，这取决于锂成核之前铜表面是否已形成SEI。提出了整合SEI壳和分段SEI壳的模型，分别描述在锂核上形成的SEI壳以及依次在铜上然后在锂核上形成的SEI壳。对于两种类型的带壳锂沉积物都观察到了“顶部溶解”，但整合SEI壳仅显示出皱纹，在锂重新沉积时可以恢复，而分段SEI壳由于顶部区域交界处引入的机械应力而明显顶部开口，成为“死”SEI，这迫使后续锂在死SEI的间隙中成核和生长。我们的工作深入了解了SEI对异质基底上锂沉积和溶解初始阶段的影响机制，揭示了SEI对锂溶解可能更具影响力，并且锂沉积物上SEI壳的空间整合对于提高沉积和溶解循环的可逆性很重要。
