Aging of lithium-ion batteries in electric vehicles: Impact of regenerative braking

In an electric vehicle, energy recovery during regenerative braking causes recharge periods of high current rate, which might damage the Li-ion traction battery. To determine the impact of regenerative braking on battery aging, an experimental cycle life study has been performed: Driving load profiles with different mag-nitudes of regenerative braking have been applied to high-energy Li-ion cells at different temperatures and states of charge (SoC). An additional calendar life study has enabled an identification of usage-dependent and usage-independent battery aging. After five months of cycling, corresponding to a driven distance of 50,000 km, cell degradation has varied substantially with different operation conditions. Our paper provides valuable new insights on the impact of regenerative braking on battery aging: A higher level of regenerative braking has generally led to reduced battery aging. This can be attributed to a reduction of lithium plating, as the depth of discharge is reduced with an increased amount of charge recovered by regenerative braking. Our study has shown that it is not the short-time recharging with high current rates, but the long-lasting charging periods, even with only low cur-rent rates, that promotes lithium plating. Moreover, the comparison of usage-dependent and usage-independ-ent battery aging has revealed that cyclic aging decreases with temperature, whereas calendar aging increases with temperature. Thus, battery life can be extended by optimized operating conditions. In this paper, we provide advice for optimizing the operating conditions for Li-ion battery systems in electric vehicles. Not only regenerative braking, but also temperature and SoC, is considered for optimal operating strategies maximizing battery life. Based on the results of our experimental study, achieving a driven distance of 100,000km with only 10% capacity fade appears to be possible. Such a low battery aging is essential to promote the spread of electric vehicles, as it reduces the total cost of ownership, which is a prerequisite for the long-term success of electric vehicles. © 2015 WEVA.