Impact of Dynamic Driving Loads and Regenerative Braking on the Aging of Lithium-Ion Batteries in Electric Vehicles

In an electric vehicle (EV), the battery load profiles differ considerably from standard laboratory test procedures, which typically apply constant currents for discharging. Due to the acceleration and deceleration of the vehicle, the battery load is highly dynamic and also contains recharging pulses with higher currents due to regenerative braking. This paper presents an experimental aging study based on a representative driving load profile to investigate battery aging in EVs. The aging study focusses on the impact of regenerative braking on battery aging at different temperatures and SoCs. Moreover, it examines different cycle depths and compares dynamic driving loads to constant current discharging. The study reveals different sensitivities of calendar aging and cycle aging to temperature: Whereas calendar aging decreases with lower temperature, cycle aging increases and also becomes sensitive to the dynamics of the load profile. Cycling up to 200,000 km exhibits that regenerative braking has a beneficial effect on the battery lifetime as it reduces the cycle depth. This lowers the capacity fade and the resistance increase considerably. Furthermore, our paper explains capacity recovery effects occurring after cycling at high SoCs only and presents basic strategies to minimize battery degradation in EVs.