金属锂固态电解质界面膜的可控构筑及原位拉曼光谱研究

Lithium metal anode is composed of Li metal (or current collector)/SEI/electrolyte interfaces，where SEI layer is inevitably formed on the Li metal surface as a result of electrolyte electroreduction. The SEI and its coupling interfaces in bridging the substrate and electrolyte play key roles, and their structures and properties will directly affect the electrodeposition behaviors of Li metal. The SEIs prepared by traditional aging method are generally complicated in spatial structure with poor physical and chemical properties, which not only promote dendrite growth easily, but also impose difficulties in the characterization of themselves. Therefore, there is still lack of deep understanding of SEI structure and formation mechanism, which hinders rational design and optimization of the interfaces for Li metal anodes. Herein, this project aims to develop the method of in situ surface-enhanced Raman spectroscopic characterization of SEI combined with the strategy of electrochemical controlled construction of SEIs. On one hand, various kinds of smooth and uniform model SEIs with adjustable structure and thickness will be prepared, which form the basis for optimizing the performances of SEIs and facilitate the establishment of in situ characterization method. On the other hand, a series of appropriate plasmon-enhancement systems pertinent to SEIs will be designed and constructed with the aid of theoretical calculations for accurately analyzing the interfacial processes of Li metal anodes. Further, spectral characteristics of SEIs will be correlated with electrochemical performances of Li metal anodes to reveal the SEI formation mechanism and effects of SEI and its coupling interfaces on the interfacial processes of Li metal anodes. This work is of significant importance in fundamental understanding of interfacial processes of Li metal anodes, which would in turn promote constructions of practical Li metal anodes.

金属锂负极由金属锂（或集流体）/SEI/电解液界面构成，SEI及其耦合界面是桥联基底和电解液的关键部分，其结构和性质直接影响锂电沉积行为。传统的自然成膜方法制备的SEI不仅理化性质欠佳、易诱导枝晶生长，且空间结构复杂、不易表征，导致缺乏对SEI形成机理的深刻理解，从而难以对金属锂界面过程进行合理调控和优化。本项目拟发展电化学可控制备和表面增强拉曼光谱原位表征的联用方法研究金属锂SEI。一方面，发展SEI可控制备策略，制备光滑均一、结构和厚度可调的金属锂SEI模型体系，为优化SEI性能、建立SEI原位光谱表征方法提供基础；另一方面，基于SEI模型体系构建合适的表面等离激元增强体系，结合理论计算，发展准确解析金属锂界面过程的原位光谱表征方法。进一步关联光谱特征与金属锂负极电化学性能，揭示SEI形成机理、探究SEI及其耦合界面对金属锂界面过程的影响，为构建高效稳定金属锂负极提供理论指导。

固体电解质界面膜（SEI）及其耦合界面是桥联金属锂负极和电解液的关键部分，其结构和性质直接影响锂负极的电化学性能。然而，目前关于SEI形成机理仍未完全阐明，影响了对相关界面过程基本问题的理解。本项目发展了电化学可控制备和拉曼光谱原位表征的联用方法研究SEI及其耦合界面，具体内容如下：1. 发展了SEI可控制备策略，依据不同电解液的理化性质，通过调控锂沉积-溶出及电解液还原动力学，制备了结构和厚度可调的SEI，为SEI的原位谱学表征提供各种结构简单、组分明确的模型参考体系，便于其研究方法学的建立。该策略不仅适用于包括醚类、碳酸酯类及离子液体在内的液态电解液体系，还可扩展至固态电解质体系中SEI的可控制备。2. 构建了基于纳米Cu-壳层隔绝纳米粒子（Au@SiO2）耦合的表面等离激元增强体系，发展了z方向上深度敏感的表面等离激元增强拉曼光谱（DS-PERS）表征方法，用于SEI及其耦合界面过程的原位无损研究。该方法具有多热点、增强因子高等特点，为研究SEI形成机理、合理优化SEI性能提供支撑。3. 利用发展的DS-PERS方法研究SEI形成机理及界面过程机制。研究发现，在不同电解液体系中，对于anode-free构型的锂负极上，锂沉积前Cu集流体表面总会首先形成一层以高态组分为主的初级Cu-SEI，锂沉积后Cu-SEI在零价Li的参与下发生化学重组并最终形成低氧化态组分为主的稳定的Li-SEI。因此，零价Li参与的化学反应对SEI的组成和性质具有重要影响。另一方面，SEI的组成和结构会显著影响SEI/电解液界面处锂离子的溶剂化结构，从而影响锂离子的去溶剂化过程及后续的锂沉积过程。基于此，我们在实际应用中发展了电化学调控策略，通过操纵电位或电流来抑制初级Cu-SEI的形成，从而直接在锂上形成更为有利的Li-SEI，由此可显著提升锂电池的循环稳定性。总之，本项目发展准确解析金属锂界面过程的原位光谱表征方法，从分子水平理解SEI形成机理、揭示SEI及其耦合界面对金属锂界面过程的影响，并由此发展电化学调控策略优化SEI及其耦合界面，为构建高效稳定金属锂负极提供理论指导。