硅/碳负极材料的界面特性及SEI膜耗锂机制研究

The solid electrolyte interphase (SEI), a passivation layer formed on electrodes, is critical to battery performance and durability of silicon anodes. However, the SEI evolution, composition, and morphology are yet to be completely understood owing to their complex structure and lack of reliable in situ experimental techniques. This project will focus on the fundamental research on the design of composite synthesis, the porosity, surface chemistry and the graphite degree related to the silicon-carbon anodes. The formation and growth mechanism of the nanometer thick SEI films will be carefully studied, which is potentially a major cause of a relatively low initial coulombic efficiency and stunted cycle life because it consumes Li ions and solvents from the electrolyte, revealing the structure-performance relationship between the electrochemical performance and porosity and surface chemistry. The surface characterization technology and significant advances in computational methods have made it possible to predictively model the fundamentals of SEI. Here molecular simulations will be used to identify deposition of SEI components and analyze the electron tunneling and Li ions transfer through model composite, guiding the optimization of electrolyte composition and quality of SEI. We believe all these findings should have a great significant in understanding the irreversible capacity loss of SEI layer and improving the performance of silicon-carbon anode.

稳定的固体电解质界面（SEI）膜对硅负极的容量发挥、循环寿命和稳定性等具有至关重要的意义。然而，由于SEI膜的形成过程非常复杂且表征测试难度极大，当前对硅/碳表面SEI膜的特性认识仍较少。本项目拟设计并制备硅/碳复合负极材料，定向调控材料孔隙结构、表面化学和结构有序性，系统研究其对首次库伦效率和循环性能的影响，阐明各变量对充电过程中SEI膜的形成、生长、演变的影响和协同作用，关联材料结构和电化学性能之间的构-效关系。根据表面分析结果对SEI组成建立模型猜想，结合量化计算和分子动力学模拟对SEI组成模型进行验证计算；同时采用分子动力学计算锂离子在SEI膜中的扩散系数以及SEI各组分的电子贯穿势垒，最终实现对电解液组成和SEI膜的可控优化。本项目的成功实施，将提高对硅/碳表面SEI膜及锂离子消耗机制的认知，对高容量硅/碳复合材料结构设计具有重要的科学意义和理论价值。

硅基材料作为新型锂离子电池负极材料具有广阔的应用前景，但仍然面临严峻的体积膨胀、首次库伦效率低、导电性差等固有缺陷。本项目从材料微观结构设计和可控制备的角度出发，通过调节硅碳复合物的形貌、孔结构、石墨化程度等，建立了硅碳负极结构和表面化学与固态电解质膜以及首次库伦效率的对应关系，从而提高了锂离子电池电化学性能和循环寿命；项目利用喷雾干燥法合成了可规模化生产的微米级多孔硅材料，探讨了具有微米级尺寸的“核-壳”结构硅碳材料对快速脱/嵌锂过程以及应力膨胀之间的内在联系，建立了复合电极材料微结构与电化学储锂性能之间的构效关系；项目采用溶剂挥发自组装法，可规模化制备了具有柔性自支撑结构的硅碳复合膜电极，通过三维网络结构的构建，提供电子转移通道的同时为硅负极膨胀提供空间。本项目的实施，对高性能、低成本的硅碳复合负极材料的理性设计与应用具有科学意义。