Model-Based SEI Layer Growth and Capacity Fade Analysis for EV and PHEV Batteries and Drive Cycles

Capacity fade experienced by electric vehicle (EV) and plug-in hybrid electric vehicle (PHEV) batteries will affect the economic and technological value of the battery pack during EV life as well as the value of the battery at the end of life. The growth of the solid-electrolyte interface (SEI) layer is a major cause of capacity fade. We studied the fade caused by SEI layer growth for eight different driving cycles (which include regenerative braking), and six charging protocols. In addition, we looked at the growth caused by varying the depth of discharge during cycling. Constant current and constant current-constant voltage charging patterns at differing rates were studied. Results showed that for half of the driving cycles regenerative braking increased the life-time energy utilization of the battery in addition to increasing the capacity during a single cycle. For the other half of the driving cycles it is shown that while regenerative braking may be beneficial during a single cycle, over the life of the battery it can decrease the total usable energy. These cases were studied using a reformulated porous electrode pseudo two dimensional model that included SEI layer growth as a side reaction.