Modeling the Si-Current Collector Interface in Li-Ion Battery

Abstract

Si is a promising anode material for Li-ion batteries (LIB) due to its high energy density. Nevertheless, the large volume variation of Si during lithiation/delithiation cycles presents a great challenge to its structural integrity in LIBs. To this end, a wide variety of Si electrode designs have been attempted. It has been shown that reducing its size to nano scale can effectively prevent the fracture of the Si electrode itself. However, failure may still occur at interfacial regions between the Si electrode and other components such as the current collector due to deformation mismatch. The detached Si becomes isolated from the electronic pathway and hence the cell capacity degrades. Understanding the deformation and stress-strain relationship at the Si-current collector interface is an important step in engineering durable, high capacity LIBs. In this work, a multiphysics microstructure-resolved model [1] was used to simulate the deformation of Si nanorods on a Ni substrate reported by Bella et al [2]. The Si was described by an elasto-plastic law with a finite strain formulation. The Li concentration dependence of the Young’s modulus and yield strength was considered. Ni was modeled as an elasto-plastic material. The interface between Si and Ni was modeled as a region with unique properties. The results revealed that the interfacial properties not only affect the deformed shape of the Si nanorod and Ni substrate but also the stress triaxiality in the system. To reproduce the deformation as in the experiment, a parameter study with different interfacial properties was carried out. The interfacial properties resulting in the best correlation with the experiment were identified. The microstructure-resolved model will then be used to investigate the structure design of LIBs with Si anode. Wu, Wei, Xinran Xiao, Miao Wang, and Xiaosong Huang. “A Microstructural Resolved Model for the Stress Analysis of Lithium-Ion Batteries.” Journal of The Electrochemical Society 161, no. 5 (January 1, 2014): A803–A813.Berla, Lucas A., Seok Woo Lee, Ill Ryu, Yi Cui, and William D. Nix. “Robustness of Amorphous Silicon during the Initial Lithiation/delithiation Cycle.” Journal of Power Sources 258 (July 15, 2014): 253–59.