锂电池体系中负极表面固态电解质界面相（SEI）对锂电池性能起到至关重要的作用。然而，SEI结构和化学组成复杂，其形成机理至今仍未完全阐明，阻碍了锂电池的发展和应用。本文从方法学角度出发，采用表面增强拉曼光谱（SERS）“借力”策略，通过优化银纳米粒子的结构并借助其外来表面局域等离激元共振作用，开展以EC-DMC为溶剂的碳酸酯类电解液体系中SEI成膜过程的原位研究。为了确保可靠的原位SERS测试，我们设计了一种三电极体系气密拉曼电池。我们利用原位SERS方法，在纳米银电极上获得了SEI成膜过程的组成和结构信息。研究表明，SEI随电位变化呈现出双层结构，其中内层由薄且致密的无机组分构成，外层由疏松的有机组分构成。同时，研究发现LEMC是EC还原的主要成分，而不是LEDC，且金属锂参与的化学反应在形成稳定SEI中的起到关键作用。此外，锂发生沉积后，由于锂与银的合金效应导致其介电常数发生变化，从而削无法进一步增强SEI的拉曼信号。本文为深入理解负极表面SEI的形成及演变过程提供依据，并为今后开展锂电池体系相关界面过程的原位研究提供借鉴。

The solid-electrolyte interphase (SEI) plays a key role in anodes for rechargeable lithium-based battery technologies. However, a thorough understanding in the mechanisms of SEI formation and evolution remains a major challenge, hindering the rapid development and wide applications of Li-based batteries. Here, we devise a borrowing surface-enhanced Raman scattering (SERS) activity strategy by utilizing a size optimized Ag nanosubstrate to in-situ monitor the formation and evolution of SEI, as well as its structure and chemistry in an ethylene carbonate-based electrolyte. To ensure a reliable in-situ SERS investigation, we designed a strict air-tight Raman cell with a three-electrode configuration. Based on the potential-dependent spectroscopic information, we revealed that the SEI formed in an EC-based electrolyte presents a double-layer structure, comprising a thin inorganic inner layer and an organic-rich outer layer. We also identified that LEMC, rather than LEDC, is the major component of EC reduction, and the critical role of metallic Li in the formation of stable SEI is preliminary explored. Nevertheless, identifying the SEI compositions is only feasible before Li deposition on the Ag surface. After the formation of Li-Ag alloys, the subsequent evolution of SEI could not be detected due to the change in the dielectric constant of Ag after the lithiation. Our work provides a real-time spectroscopic method for investigating interfacial processes of anodes, which is beneficial to the understanding of SEI formation and evolution and thus provides guidance for the development of rationally designed SEI in Li-based batteries.