关键词: 锂离子电池组, 热特性, 热一致性, 等效电路-热模型

Abstract:

Variations in the characteristic parameters of individual cells within a Li-ion battery pack—such as SOC, capacity, and internal resistance—can lead to uneven thermal distribution due to electro-thermal coupling, thereby impacting the pack's performance and safety. This paper examines the dynamic characteristics of lithium batteries at different temperatures and depths of discharge and develops a second-order RC equivalent circuit-thermal coupling model to analyze how inconsistencies in SOC, capacity, and internal resistance affect the thermal behavior of both parallel and series battery packs through numerical simulations. The study quantifies differences in energy release capacity, heat generation rate, and temperature distribution under various connection configurations. The results indicate that when SOC inconsistency is present, the parallel-connected battery pack releases 379.575 Ah of energy due to the self-balancing effect, which is higher than the 366.024 Ah released by the series-connected pack. However, the standard deviation of the heat generation rate and the maximum temperature deviation in the parallel-connected pack are 2.265 W and 0.62 ℃, respectively—significantly higher than those of the series-connected pack (0.475 W and 0.275 ℃). This suggests that the series configuration provides better thermal consistency. When capacity inconsistency occurs, the heating rate of the parallel-connected pack exhibits greater fluctuations due to variations in branch currents. The standard deviation of its temperature is 0.421 ℃, which is 0.188 ℃ higher than that of the series-connected pack (0.233 ℃). Additionally, the maximum temperature difference reaches 1.222 ℃ in the parallel-connected pack, compared to 0.670 ℃ in the series configuration, further emphasizing the superior thermal uniformity of the series connection. In cases of internal resistance inconsistency, the average temperature of the series-connected battery pack is slightly higher (33.233 ℃) than that of the parallel-connected pack (33.204 ℃). However, the standard deviation of temperature and heat generation rate in the series-connected configuration (0.19 ℃ and 0.097 W) are lower than those in the parallel-connected pack (0.215 ℃ and 0.405 W). This suggests that the series-connected mode can effectively mitigate thermal imbalances caused by internal resistance variations. Further quantitative comparisons reveal that SOC inconsistency has the most significant impact on thermal consistency, with the maximum difference in heating rate reaching 6.499 W in parallel and 1.261 W in series. Capacity inconsistency results in the largest temperature difference in parallel-connected packs (1.222 ℃), which is 1.8 times greater than that of the series-connected pack. Additionally, under internal resistance inconsistency, the standard deviation of temperature in series-connected packs is only 88% of that in parallel-connected ones. In conclusion, series-connected battery packs demonstrate better thermal consistency when individual cell parameters vary, whereas parallel-connected packs release more energy but require enhanced thermal management to address the increased risk of temperature fluctuations. This study provides crucial data for optimizing thermal models and designing cooling systems for electric vehicle battery packs, offering valuable insights into improving battery safety and longevity.

Key words: Li-ion battery packs, thermal characteristics, thermal consistency, equivalent circuit-thermal model