金属锂及硅负极材料表面膜三维结构与化学组成研究

The surface film problem is one of the most important issues in the development of high energy density lithium battery. It plays a significant role in the rate capability, cycling life and safety of lithium battery. Up to now, the chemical compositions of the surface film of some typical electrolyte/electrode materials system have been obtained by using various techniques, which helps us understand the interfacial problems and improve the battery performance. However, so far as we know, accurate measurements of the thickness, transport behavior, mechanical property, coverage, solubility of the surface film are still not available currently. In order to obtain this information, we developed an atomic force microscopy based method, scanning force curve, and have successfully applied to the silicon thin film anode for lithium ion batteries. We hope to further expand this method to the lithium metal/silicon anode in the current proposal, in the purpose of acquiring the 3D structures of the surface film. The chemical compositions can also be obtained via EIS, XPS, SIMS, Soft-XAS and so on. Based on our work, we expect to in-depth understand the surface film formation mechanisms of lithium metal/silicon anode upon cycling, pave the way for their pratical application in the high energy density batteries. In addition, we will attempt to develop a standard electrolyte additive evaluation procedure (based on the scanning force curve method) for the lithium batteries.

锂电池表面膜的性质对电池倍率性能、循环寿命及安全性具有重要的影响。是开发高能量密度锂电池需考虑的核心问题之一。目前对表面膜相关问题的研究主要通过多种分析手段，获得了在典型材料体系中表面膜的成分信息。而对表面膜的厚度、电/离子输运、力学属性、覆盖度、溶解性及电化学稳定性等性质的精确了解还有一定的距离。为此，我们发展了原子力显微镜扫描力曲线方法，并在硅薄膜负极上实现，初步得到在标准电解液体系表面膜的上述性质。通过本项目，希望将此方法进一步应用于金属锂及硅负极材料，研究其在多种电解液（添加剂）体系、不同化成制度等条件下表面膜的三维结构，结合阻抗谱、光电子能谱、二次离子质谱,、软X射线吸收谱等手段研究这两种材料表面膜的综合性质。以期深入理解金属锂及硅负极材料表面膜的形成机理，获得提高界面稳定性的方法，为其在高能量密度锂电池中的应用提供科学基础。同时将扫描力曲线方法开发成标准化评价研究电解液的方法。

界面问题是影响锂电池性能及安全性的重要问题，理解界面反应机理，有效地提升界面稳定性，是目前研究的热点。本文依托于承担单位建设的互联互通惰性气氛材料综合测试分析平台，利用原子力显微镜力曲线方法研究了硅负极材料界面膜的覆盖度、力学属性等；采用X射线光电子能谱、二次离子质谱等手段分析了硅负极材料，金属锂负极材料在循环后表面反应产物的成分和形成机理等，同时研究了电解液添加剂在界面反应过程中的作用机理。目前项目所在的团队已把硅负极材料进行中试研究阶段，并成立了孵化公司，建成了年产2000吨生产线。而本项目的研究结果也为硅负极材料的产业化提供了技术支持。