Tin oxide (SnO₂) is widely recognized as a promising negative electrode material for high capacity lithium (Li)-ion batteries due to its high-energy density. Recent experiments^1–3 using high-resolution Transmission Electron Microscopy (TEM) show that the lithiation process in SnO₂ nanowires occurs in two stages. Initially, rapid Li diffusion occurs from one end of the nanowire to the other through narrow stripes along the electrode. This stage is followed by a second stage where Li diffuses through the bulk at a much lower speed throughout the electrode leading to amorphization. In order to understand this complex phenomenon we have employed a finite element (FE) modeling in conjunction with previous in-situ TEM experiments³ to study the lithiation of SnO₂ nanoelectrodes. In the experimental work, SnO₂ nanowire lithiation process was characterized using in-situ TEM where the SnO₂ nanowire was placed on the negative side of the in-situ setup and was brought in direct contact with the Li source.¹

The idea behind FE in this context is to formulate the lithiation process using physical models which provide results consistent with experimental observations. The model is based on the understanding that in SnO₂ nanowire a slip plane is created due to non-perfect contact of the source or defects and the stress at the slip planes leads to significantly higher diffusion coefficient.¹

The developed constitutive model which has been implemented in FE, captures the formation of striped diffusion regime and corresponding electrode’s expansion during the lithiation of SnO₂. In particular, the model incorporates the formation of stripes by using a variable nonlinear diffusivity coefficient which is a function of the concentration-dependent stress. The structural changes associated with the Li diffusion/intercalation in the electrode geometry are modeled using a 2D plane strain assumption and linear elastic material. The results from the model show a clear formation of striped diffusion regime due to the induced stresses, at low concentrations of Li. This results in a small strain of 10% within the nanowire and is followed by a bulk diffusion and expansion at higher concentrations. Thus, the simulations allow for the spatiotemporally resolved prediction and analysis of Li diffusion/intercalation and its influence on the electrode performance under the realistic operation conditions.

References

1. A. Nie, L. Y. Gan, Y. Cheng, H. Asayesh-Ardakani, Q. Li, C. Dong, R. Tao, F. Mashayek, H. T. Wang, U. Schwingenschlgl, R. F. Klie, and R. S. Yassar, ACS Nano, 7, 6203–6211 (2013).

2. L. Q. Zhang, X. H. Liu, Y. C. Perng, J. Cho, J. P. Chang, S. X. Mao, Z. Z. Ye, and J. Y. Huang, Micron, 43, 1127–1133 (2012).

3. J. Y. Huang, L. Zhong, C. M. Wang, J. P. Sullivan, W. Xu, L. Q. Zhang, S. X. Mao, N. S. Hudak, X. H. Liu, A. Subramanian, H. Fan, L. Qi, A. Kushima, and J. Li, 330, 1515 LP – 1520 (2010).