多尺度内聚力有限元方法在锂离子电池中的应用

Application of Multiscale Cohesive Finite Element Method in Lithium-ion Battery

锂离子电池电极材料中锂离子扩散与结构应力的耦合作用是影响电池性能和安全的重要因素,为了模拟该过程中的浓度扩散和应力演化,提出了一种基于多尺度内聚力有限元方法的扩散-应力耦合模型,通过将化学能与应变能相结合,分别建立浓度场及应力场控制方程并推导了其有限元格式。以负极材料薄膜硅为例建立了二维的数值算例模型,计算了无晶界和含晶界情况下,不考虑材料损伤的电极材料中由于锂离子嵌入所引起的浓度及应力变化。多尺度有限元模型从原子尺度出发计算结构应力,丰富了材料的本构关系和物理性质,内聚力单元在描述界面处的物理特性如浓度、应力时具有很高的灵活性和有效性,该模型的提出为更准确地理解锂离子电池电极中的锂离子扩散-应力耦合过程提供了理论方法。

The coupling of lithium-ion diffusion and stress in the electrode material of lithium-ion battery is an important factor affecting the performance and safety of the battery.In order to simulate the concentration variation and stress evolution in this process,a diffusion-mechanics coupling model based on the multiscale cohesive finite element method is proposed,where the controlling equations of stress field and concentration field are established by combining the chemical energy with the strain energy and the finite element formula of this model is deduced.A two-dimensional numerical calculation of the concentration and stress variation caused by lithium ion intercalation in the electrode in the case of grain boundaries-free and grain boundaries-containing is both established by taking the thin-film silicon as an example without considering the material damage.With the atomistic information,the mesoscale constitutive relations and physical properties of materials are enriched.The cohesive elements have high flexibility and effectiveness in describing the physical properties such as concentration and stress at the interface.With the newly coupled approach,a more realistic understanding of diffusion-mechanics coupling process in electrodes of lithium-ion battery can be provided.