Model-Based SEI Layer Growth in EV and Phev Batteries for Standard Drive Cycles

Abstract

Capacity fade in electric vehicle batteries is caused through a number of mechanisms. Solid Electrolyte Interface (SEI) layer growth caused by side reactions at the battery anode is one of these mechanisms that results in loss of battery power and energy capacity. Reducing the growth of this layer can help increase battery life and overall utility of electric vehicles, especially near the end of their service life. We use a model based approach to study how the SEI layer grows during different types of charging, specifically looking at how the regenerative braking portion of driving will contribute to SEI layer growth. Eight different drive cycles were used to analyze how different driving patterns contribute to SEI layer growth. The battery model used for the study was a porous electrode pseudo two dimensional model.1 A mathematical reformulation of the model was used to increase computational efficiency and speed without greatly reducing model accuracy.2 Three different SEI layer growth equations from literature were studied for EV charging.3-5 SEI growth was studied for both charging and regenerative braking, during which the battery is being charged for short periods of time during driving cycles that are predominantly discharge. Results show rates of SEI growth for driving duration (by time) and length (by distance traveled) and analyze similarities in the driving cycle characteristics that may lead similar SEI layer growth rates. Additionally, results look at the effects of different depth of discharge during cycling on the battery and how DOD affects the overall SEI layer growth.6 As EV batteries continue to go through cycles, the effects of SEI growth caused from different types of driving will become more pronounced. The results shown will help reveal how that SEI growth can be reduced through driving patterns.