A Comprehensive Study on Influence of Battery Thermal Behavior on Degradation and Consistency

An electro-thermal coupling model is established for a parallel-connected pack with cooling on the two ends of the stack of cells. Unlike the traditional battery model, this model can calculate the branch current in the pack and precisely describe the pack performance. Experiments are implemented and it is proved that the proposed model has a high prediction accuracy. Then the proposed model is applied to study the mechanism on how the pack temperature and its temperature difference affect its electrical consistency and lifespan. According to the results, the state of charge (SOC) homogeneity and state of health (SOH) of pack are related with the temperature variation of the pack and its temperature, respectively. Enhancing the cooling can reduce the pack temperature and extend the pack lifespan. The pack SOH fall reduces to 0.33%, when the air temperature and the battery initial falls to 10 °C and the heat transfer coefficient between the battery and the air increases to 220 W/( $\text{K}\cdot \text{m}^{2}$ ). However, this method produces a large temperature gradient, enlarges the branch current difference, and aggravates SOC inhomogeneity in the pack. When the heat-transfer coefficient increases from 5 to 220 W/( $\text{K}\cdot \text{m}^{2}$ ), the temperature variation inside the pack rises by 737.8%, making SOC difference go up by 892%. Moreover, the most suitable temperature difference for the SOC homogeneity is not traditional 5 °C, but rises with ambient temperature and temperature of cooling medium. It is the same for that of SOH. The research results also indicate that the control of pack temperature and that of temperature different are contradictory and they should be well balanced to achieve a good SOC homogeneity and long pack lifespan.