Mathematical Model for Combined Effect of SEI Formation and Gas Evolution in Li-Ion Batteries

In this study, a mathematical model to investigate the combined effect of SEI film formation and gas evolution over the degradation of Li-ion cells is developed. A Li-ion cell is simulated for three discharge/charge rates until 80% of the rated capacity is irreversibly lost in side reactions. The model shows that the thickness of SEI film and volume of gases evolved is between 0.03–0.22 μm and 1.6–10.6%, respectively. It is shown that, in addition to greater diffusion limitations, capacity degradation at higher cycling rates is faster due to reduction in cyclable lithium caused by its accumulation in the negative electrode.