Abstract:

Lithium-ion batteries using graphite as the negative electrode material are widely used in the field of new energy, but their capacity attenuation after long-term charge and discharge cycles will significantly shorten the service life of the battery. One of the primary factors influencing battery cycle life is the growth of the solid electrolyte interface (SEI) layer on the anode surface. This growth is influenced by the electrolyte composition, preparation process, and the structure of the graphite material. In this study, we develop a model to describe battery capacity decay based on the growth reaction of the SEI film and investigate the impact of graphite structure on capacity decay and SEI film growth through simulations. The results show that the larger the particle size of the anode material is, the faster the SEI film thickness increases and the battery life is significantly reduced. Throughout the charge/discharge cycles, the initial cycle experiences the most rapid capacity decay, then the aging rate slows down and stabilizes as the SEI film thickness increases in subsequent stage. The reduction in the diffusion coefficient of the solvent in the SEI film and the porosity of the SEI layer will slow down the battery capacity fading rate. Notably, the inward diffusion of solvent through the SEI film to the anode surface is believed to be the rate-determining step in the continuous growth of the SEI film. These findings provide fundamental insights and guidance for optimizing the preparation of anode coatings.

Key words: electrochemistry, lithium-ion battery, mathematical modeling, electrode electrolyte interface, graphite

摘要：

以石墨为负极材料的锂离子电池在新能源领域应用广泛，但其长时间充放电循环后的容量衰减会显著缩短电池的使用寿命。负极表面固体电解质界面层（SEI）是影响电池循环寿命的主要因素之一，其生成反应除了受电解质组成和制备工艺影响外，还取决于石墨负极材料的结构。基于SEI膜的生长动力学，构建了电池容量衰减模型，模拟计算了石墨负极颗粒粒径对于电池容量衰减及SEI膜生长过程的影响。结果表明，负极材料颗粒粒径越大，SEI膜厚增加速度越快，电池使用寿命显著降低；在充放电循环过程中，首次循环容量衰减速度最快，随着后期SEI膜厚的增加，老化速率减缓并趋于稳定；溶剂在SEI膜中的扩散系数和SEI层孔隙率的降低，会减缓电池容量衰减速度；溶剂通过SEI膜向内扩散至电极表面的步骤是SEI膜连续生长过程中的控速步骤。研究结果可为锂离子电池石墨电极涂层制备工艺优化提供基础知识及指导。

关键词: 电化学, 锂离子电池, 数学模拟, 电极电解质界面, 石墨