二次锂电池表界面电子结构的同步辐射光谱学研究

This project plans to employ the SiPME2 soft x-ray absorption and photoemission spectroscopy beamline and hard x-ray absorption fine structure spectroscopy beamline, combined with the thin-film electrode growth and in-situ characterization techniques, to systematically study the electronic structures of surfaces/interfaces in Li batteries, which is an important but the least understood scientific problem. We plan to extensively investigate the formation, growth, and evolution mechanism of interfaces in novel Li-ion batteries by multiple spectroscopic techniques with elemental selectivity and surface sensitivity. In particular, we plan to explore, from the point of view of electronic structure, the evolution pattern of interfacial electron double layer, ion transport and diffusion, local distortion of crystal structure, strength of orbital hybridization, interfacial band bending, and the relationship between these fundamental physical mechanisms and macroscopic properties such as the increase of impedance, degradation of electrolyte, and capacity fading. The ultimate goal of this project is to provide new scientific evidences to improve the battery performance. Further, this project will promote the experimental capability of the related beamlines for the in-situ characterization of electronic structure, and provide novel methodology and platform for the Li-battery research.

本项目拟利用上海同步辐射光源新建的SiPME2软X光吸收谱和光电子谱线站，硬X光XAFS线站，结合薄膜电极制备和原位表征技术，对锂电池表界面电子结构这一关键科学问题开展系统研究。我们计划结合多种X光谱学方法，利用谱学方法的元素选择性和表面敏感性，广泛研究多种新型锂离子电池和全固态电池中表界面的形成、生长和变化机制。特别是从电子结构的角度揭示界面双电层、离子输运和扩散、局域晶格扭曲、轨道杂化强度、界面能带弯曲等微观机制的演化规律，以及表界面基本物性与界面阻抗增加、电解质降解、容量衰减等宏观性能之间的构效关系，为进一步提高锂电池性能提供新的科学依据。通过项目的实施，还将提高相关实验线站的原位电子结构实验能力，为我国锂电领域提供新的表征手段和研究平台。

本项目依托上海光源吸收谱学实验站，发展了适用于固-气、固-液和固-固界面的原位测量装置。在硫化物和氧化物电极中开展了阴离子活化的电子结构研究，系统阐明了过渡金属与配体阴离子的杂化作用对体相阴离子活化的影响；在此基础上，初步澄清了活化过程对电解液界面演化的影响。系统研究了石榴石型电解质与正负极的界面稳定性，阐明了电解质-正极界面稳定的起源以及电解质表面碳酸锂积聚的机制，提出了利用转化反应改善锂负极-电解质界面稳定性的新思路，为全固态电池的商业化提供了指导。本项目整体上按照计划执行，达到了既定目标，已发表文章15篇，获得专利授权1项，培养研究生5名及博士后2名。