A fundamental understanding of solid-electrolyte interphase (SEI) is paramount importance for controlling the cycling performance of rechargeable lithium metal batteries. The structural and chemical evolution of SEI with respect to electrochemical operating condition remains barely established. Here we develop a unique method for imaging the evolution of SEI formed on the Cu foil under sweeping electrochemical potential. By using cryogenic TEM imaging combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy electronic structure analyses, we reveal that, for the vinylene carbonate (VC)-free electrolyte, the SEI formed at 1.0 V is a monolithic amorphous structure, which evolves to amorphous matrix embedded with Li₂O particles as the voltage decreases to 0 V. In the case of VC-containing electrolyte, the SEI is featured by an amorphous matrix with Li₂O particles from 1.0 V to 0 V. The thickness of SEI formed on Cu foil increases with decreasing voltage. Associated with the localized charge modulation by the surface topographic feature and defects in the Cu foil, the SEI layer shows direct spatial correlation with these structural defects in the Cu. In addition, upon Li deposition, the SEI formed on the Li metal has similar thickness with, but different composition from the SEI formed on the Cu foil at 0 V. Those results provide insight toward SEI engineering for enhanced cycling stability of Li metal.

对固体电解质中间相（SEI）的基本了解对于控制可充电锂金属电池的循环性能至关重要。相对于电化学操作条件而言，SEI的结构和化学演化仍未确定。在这里，我们开发了一种独特的方法，用于在广泛的电化学势下成​​像形成在铜箔上的SEI的演变。通过将低温TEM成像与能量色散X射线光谱和X射线光电子能谱的电子结构分析相结合，我们发现，对于不含碳酸亚乙烯酯（VC）的电解质，在1.0 V时形成的SEI是整体的无定形结构，演变成嵌入Li _2的非晶基体随着电压降低至0 V，O颗粒逐渐增多。在含VC的电解液中，SEI的特征是非晶态基质中含有1.0 V至0 V的Li ₂ O颗粒。电压。通过表面形貌特征和铜箔中的缺陷与局部电荷调制相关，SEI层显示出与铜中这些结构缺陷的直接空间相关性。另外，在Li沉积时，在Li金属上形成的SEI的厚度与在0 V下在Cu箔上形成的SEI的厚度相似，但组成不同。这些结果为SEI工程技术提供了见识，以增强Li金属的循环稳定性。