新型三维三明治状框架结构复合电极材料的扩散诱导应力分析

Diffusion-induced stress analysis of a new composite electrode material with 3D sandwich-like frame microstructure

制备出更优异的电极材料是提高锂离子电池性能和电化学储能效率的一种关键策略。针对具有三维框架微结构的三明治状复合电极材料,将"自然"特征函数展开方法用于多层活性材料离子扩散问题的解析求解,使求解过程更简捷,也更符合物理实际。在此基础上,根据框架结构刚度的不同,建立力学概念模型,利用叠梁理论在细观尺度研究了电化学扩散过程中应力的演化规律及应力缓冲的机理。最后,研究了厚度比、模量比对应力的缓冲效应。结果表明:柔性结构更有利于电极内部应力松弛,进而保证电极的力学稳定性和结构完整性;应在保证外部活性层应力尽可能小的情况下,适当增加夹心层的厚度;在保证其他材料属性符合要求的前提下,要尽可能选择模量比较小的两种活性材料。

Preparing more excellent electrode materials is a key strategy to improve the performance and electrochemical energy storage efficiency of lithium ion batteries. Herein, focusing on the composite electrode material with 3 D sandwich-like frame microstructure, the“natural”eigenfunction expansion method is used in ion diffusion of multilayer active materials, which makes the solution simple and consistent with the physical reality of the problem. The mechanical conceptual model is established for different rigidhty of the frame structure, and the evolution of stress and stress buffering mechanism during the electrochemical diffusion are studied at the mesoscale based on the laminated beam theory. The results show that the flexible structure is more conducive to the internal stress relaxation of the electrode, thus ensuring the mechanical stability and structural integrity of the whole electrode. Finally, the effect of thickness ratio and modulus ratio on stress buffering are investigated, which indicates that two materials with similar modulus should be selected and the thickness of the inner layer should be appropriately increased on the condition that the stress in the outer layer is as low as possible.