Temperature Characteristics Research on LiFePO4 Cells Series Battery Pack in Electric Vehicles

Due to cell-to-cell variations in battery pack, it is hard to manage cells of the battery pack safely and effectively. As a result, the battery pack performance is rapidly degraded, which in turn spread the differences in individual cells. Ambient temperature is a significant factor that influences characteristics of lithium-ion battery and cells variations in the pack. This paper tries to put effort on researching the temperature characteristics of cells series battery pack. The battery model parameters identification tests are designed to analyze the inconsistency characteristics of cells (such as open circuit voltage (OCV), ohmic and polarization resistances, and polarization capacitance) under various ambient temperatures. The results indicate that ohmic and polarization resistances are most significantly increased as the temperature decreases, while the opposite is true for OCV. The variation of cells inconsistency characteristics is obvious along with the temperature change.