ES240 Project: FEM simulation of intercalation-induced stress in amorphous Si thin film anode of Li-ion battery

Intensive research is currently ongoing to develop rechargeable lithium-ion batteries with higher capacities, for the application in portable electronic devices, electric vehicles, etc. Silicon has been an attractive candidate for the anode material because it has the highest theoretical capacities, i.e., 4000 mAh/g, which is ten times higher than that of the existing carbonaceous graphite anode materials. However, silicon-based anode materials are limitedly applicable to the current lithium-ion battery, due to the fact that the capacity fading in most of Si-based anodes suffers from the first few charge/discharge cycles. It has been experimentally identified that volume expansion by 300%~400% of bulk Si during lithium ion insertion and extraction result in cracking and pulverization, and consequently the capacity failure. This crucial hurdle has to be overcome before the Si-based anode materials become commercially applicable. Si-based thin film deposited on metallic substrate has been proposed to be a promising technology because it shows better capacity retention in a number of experiments. The thin film, however, also cracks for crystalline thin film and delaminated eventually for amorphous film leading to the failure of the anode. The failure mechanism of the thin film is not well-understood to date. In order to better understand the failure mode and corresponding failure mechanism of Si-based thin film, amorphous Si deposited on copper substrate is going to be under study in this project, to identify the intercalation-induced internal stress. The numerical simulation method is adopted by using ABAQUS.

Ambitiously three main objectives lie in this project,

1): estimate the internal stress induced by lithium ion intercalation and extraction

2): identify the failure mode and the failure mechanism of amorphous thin film

3): learn finite element method and ABAQUS

Basically two models are included in the numerical simulations, solid stress-strain model with existing concentration gradient and partial differential equation of diffusion, i.e.,

Where c is the concentration change of the diffusion species, Ω is the partial molar volume of solute,J is the species flux. Equipped with these two relations, the internal stress distribution is expected to be numerically obtained.

Reference:

[1]: L. Y. Beaulieu, T. D. Hatchard, A. Bonakdarpour and M. D. Fleischauer. J. Electrochem. Soc., 150(11), A1457-A1464 (2003).

[2]: Xiangchun Zhang, Wei Shyy and Ann Marie Sastry. J. Electrochem. Soc., 154(10), A910-A916 (2007).