For future BEV applications, use of Si-containing negative electrode shown benefits to meet aggressive cell energy density targets of 750 Wh/L which are driven by performance objectives. However, using Si-containing negative electrodes comes with a drawback – the cell volume increases and decreases significantly during Li⁺ intercalation and deintercalation. Cell expansion and contraction are major concerns for battery pack and module developers. This talk will be an effort to understand the behavior of cell expansion due to formation and cycling, with measurements made by a system that uses a Linear Variable Differential Transformer (LVDT) sensor. Data showed that reversible expansion during charge/discharge in a cycle is a function of cell capacity and it can diminish with increasing initial compression. Irreversible expansion during cycling grows linearly with the number of cycles and is reduced with initial compression of the cell. With initial compression of 45 psi, measurements showed 3% cell expansion during formation, 4% reversible expansion in a charge/discharge cycle with C/5 rate, and 12% irreversible expansion over 220 cycles.

We also formulated a model that describes the diffusion, volume change and mechanical compression coupled with multi-site-multi-reaction theory of the porous electrodes and we apply the treatment to battery cells with silicon as anode active material. Changes in the porosity, cell thickness and cell electrochemical resistance was calculated due to increase in active material volume and mechanical compression. Model simulations (Figure 1) show that during the C/5 charge cycle, particle expands by 10%, porosity of the electrode decreases by approximately 8%. The model can be exercised to evaluate the operating regime for meeting targets and design considerations. Simulation studies revealed the importance of compression pressure and the spring constant on cell expansion.