金属锂是新一代二次电池负极材料的重要候选者，但易产生枝晶这一缺点阻碍了其实际应用。构筑稳定有效的固体电解质中间相（SEI膜）是抑制锂枝晶化的重要途径，而这亟需人们更深入地理解SEI膜的形成和工作机制，特别是其中涉及的界面分子过程。本项目中，我们拟采用具有界面选择性的电化学原位和频光谱技术，对一系列模型化的锂金属SEI膜体系进行研究，探测含氟有机分子、有机磷酸酯分子等添加剂/预处理剂在锂表面的吸附组装过程及其与溶剂分子和电解质离子之间的相互作用，着重关注1）SEI膜有机层的分子组成和取向，及其动态变化；2）这些分子因素与SEI膜阻抗之间的关联；3）SEI膜附近的内建电场及其对锂离子枝晶化的影响。这些研究将揭示SEI膜有机外层的生成和演化机制，以及其在锂离子扩散和沉积过程中扮演的角色，将有助于从分子层面厘清SEI膜的工作和失效机制，为合理设计SEI结构以有效保护和利用锂金属电极提供理论依据。

Metallic lithium is an important candidate for anode material in the next-generation of secondary batteries, whereas its practical application is hindered by the Li-dendrite growth problem. A key way to solve the problem is to construct a stable and effective solid electrolyte interphase (SEI) on the metal surface. Deeper understanding of the formation and working mechanisms of SEI is strongly demanded, especially in regard of the interfacial molecular dynamics. In this project, we propose to use the interface-selective electrochemical in-operando sum frequency generation (SFG) spectroscopy to investigate a series of model systems consisting of simplified but still effective SEI on metallic lithium. The adsorption and assembly of a variety of fluorine-containing organic molecules and organic phosphates on lithium surface will be monitored and the interactions between these additives (or pretreating reagents) and the solvent molecules and electrolyte ions will be probed. Particular attention will be paid on 1) the molecular compositions and orientations in the organic outer layer (OOL), and their dynamic variations during charging/discharging; 2) the relationships between these molecular factors and the electrochemical impedance of the model SEI films; 3) the intensity and range of the built-in electric field near the SEI films and the effect of the field on Li-dendrite growth. The above studies will help us to reveal the formation and evolution mechanism of the OOL of SEI, and the role of OOL during the lithium ion diffusion and deposition processes. Deep insights will be gained into the working and failure mechanisms of SEI, which will provide theoretical guidance for the rational design of SEI structure to protect and make good use of metallic lithium electrode.