&nbsp;Pulse charging is an effective charging method to improve lithium ion battery’s performance and shorten charging time. The objective of this work is to study how the pulse charging method shortens charging time while improving the performance of battery at low ambient temperature. Both experimental testing and numerical simulations are implemented in this research. Firstly, this work designs and conducts a series of experiments on the pulse charging method. Various pulse charging patterns are implemented for fast charging lithium ion batteries at low temperature. The cut-off point of pulse charge is determined through a preliminary experiment. A temperature limit of 0°C is chosen as the cut-off point, where the temperature rise caused by pulse charging is high enough while the total charging time is not too long. The pulse charging pattern is characterized by two parameters in this work: the pulse discharge current rate and the protection capacity ratio. The protection capacity ratio is defined as the ratio of the pulse discharge capacity to the pulse charge capacity which relates the pulse rate and pulse duration. The Taguchi method is employed to design the experiment to further study the effect of these two parameters. The pulse discharge current rate is set to be 4C, 8C and 12 C, where high discharge rates can accelerate the temperature rise at low temperature. The protection capacity ratio is set to be 5%, 25% and 50%. The experimental results show that the pulse charging method saves about 11% of the charging time with 25% of protection capacity ratio and 12C pulse discharge rate compared with the traditional 1C CC-CV charging method when the ambient temperature is -8.5oC. The protection capacity ratio is found to have the greatest effect on the total charging time. Secondly, an electrochemical and thermal coupled model is developed to reveal the working principle of the pulse charging method. After model validation, the model is used to study the cell temperature, the lithium ion concentration distribution and the electrolyte potential distribution inside the battery under various pulse charging conditions at low temperature. The cell temperature rises faster with the pulse charging method at low ambient temperature than with the conventional constant current-constant voltage charge method.&nbsp; High charging temperature leads to better lithium diffusivity thus saving charging time.&nbsp;&nbsp; Meanwhile, the model results show that the pulse charging method results in a more uniform lithium ion distribution inside the battery thereby improving the lithium ion battery charging performance. Both results are consistent with the experimental testing. The work presented in the research provides evidences that the pulse charging method can improve the battery’s performance and save charging time at low ambient temperature.

Investigating Effects of Pulse Charging on Performance of Lithium-Ion Batteries at Low Temperature

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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