Investigation into the Effect of Thermal Management on the Capacity Fade of Lithium-ion Batteries
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The popularity of electric (and hybrid) vehicles has raised the importance of effective thermal management for lithium-ion batteries, both to prevent thermal runaway leading to a fire hazard, and to minimize capacity fade for longer lifetime. In this research, the focus was on the effect of thermal management on the capacity fade of lithium-ion batteries. A battery thermal management system will impact the battery operation through its temperature, thermal gradient and history, as well as the cell-to-cell temperature variations in a battery module. This study employed AutoLionST, a software for the analysis of lithium-ion batteries, to better understand capacity fade of lithium-ion batteries, complemented by the experimental investigation. Experimental capacity fade data for a lithium-ion battery cycled under isothermal, 1C charge/discharge conditions was measured first, which was used to validate the numerical model. Then the software’s ability to model degradation at moderate to lower temperatures of around 20°C was investigated with simulation of battery capacity under isothermal conditions for a variety of operating temperatures. The next phase of the study modeled battery capacity fade under a variety of different operating conditions. In the first set of simulations, three different base temperatures, constant discharge rates, and heat transfer coefficients were considered. In the second set of simulations, a fixed-time drive cycle was used as the load case to model a typical day’s worth of driving, while varying the base temperature, charge voltage, and heat transfer coefficient. These simulations were repeated considering regenerative braking. It was found that temperature has the largest direct impact on the capacity fade which is expected based on prior sutdies. Further, it was found that thermal management does have a significant impact on capacity fade, as effective thermal management is capable of preventing significant battery temperature rise. As concluded from the constant discharge rate simulations, effective thermal management is most crucial at high discharge rates, which will result in high heat generation. It was also concluded from both constant discharge rate and drive cycle simulations, that thermal management is much more effective at preventing capacity fade at battery temperatures close to 20°C. In the drive cycle simulations, using the same discharge profile, there is a much more significant spread in battery capacity between high and low heat transfer coefficients for a lower base temperature (20°C) compared to higher base temperatures (35°C and 50°C). As well, it was shown that using a lower charge voltage will result in slightly less capacity fade over cycling. Additionally, using regenerative braking makes it more realistic to use lower charge voltages, since the battery pack can be recharged during operation, thereby increasing driving range, while preventing increased capacity fade. The final phase showed that effective thermal management would be even more imperative for more intense and realistic driving styles. It was shown that different driving styles can result in significant rises in heat generation and hence battery temperature. From previous conclusions this implies that much intense driving (high acceleration) can result in a higher need for effective thermal management.
Cite this work
Andrew Carnovale (2017). Investigation into the Effect of Thermal Management on the Capacity Fade of Lithium-ion Batteries. UWSpace. http://hdl.handle.net/10012/11144