Thermal characterization and thermal consistency study of battery packs based on differences in monomer characteristic parameters

doi:10.19799/j.cnki.2095-4239.2025.0127

Abstract

Abstract:

Variations in the characteristic parameters of individual cells within a lithium-ion (Li-ion) battery pack-such as state of charge (SOC), capacity, and internal resistance-can lead to nonuniform thermal distribution due to electrothermal coupling, thereby affecting the overall performance and safety of the pack. This study investigates the dynamic behavior of lithium batteries at different temperatures and depths of discharge, and establishes a second-order RC equivalent circuit-thermal coupling model to examine how inconsistencies in SOC, capacity, and internal resistance influence the thermal behavior of series- and parallel-connected battery packs through numerical simulations. The study quantifies disparities in energy release, heat generation, and temperature distribution across various connection configurations. Results show that, under SOC inconsistency, the parallel-connected pack releases 379.575 Ah due to the self-balancing effect-higher than the 366.024 Ah released by the series-connected pack. However, the standard deviation of the heat generation rate and maximum temperature deviation in the parallel configuration are 2.265 W and 0.62 ℃, respectively, which are significantly greater than those in the series configuration (0.475 W and 0.275 ℃), indicating superior thermal consistency in the series-connected arrangement. For capacity inconsistency, the parallel configuration exhibits greater fluctuations in heating rate due to uneven branch currents, with a temperature standard deviation of 0.421—0.188 ℃ higher than that of the series-connected pack (0.233 ℃). The maximum temperature difference reaches 1.222 ℃ in the parallel configuration, compared to 0.670 ℃ in the series, further highlighting the enhanced thermal uniformity of the series layout. Under internal resistance inconsistency, the average temperature of the series-connected pack is marginally higher (33.233 ℃) than that of the parallel configuration (33.204 ℃), yet the standard deviations of temperature and heat generation rate in the series-connected pack (0.19 ℃ and 0.097 W) remain lower than those in the parallel-connected one (0.215 ℃ and 0.405 W). This suggests that the series configuration effectively mitigates thermal imbalance induced by internal resistance variations. Further quantitative comparison reveals that SOC inconsistency has the most pronounced effect on thermal consistency, with maximum differences in heating rate reaching 6.499 W in the parallel configuration and 1.261 W in the series. Capacity inconsistency leads to the largest temperature difference in the parallel pack (1.222 ℃), which is 1.8 times greater than that in the series. For internal resistance inconsistency, the temperature standard deviation in the series configuration is only 88% of that in the parallel. In conclusion, series-connected battery packs exhibit better thermal consistency under parameter inconsistencies, while parallel-connected packs offer greater energy output but demand more robust thermal management to mitigate temperature fluctuations. These findings provide a quantitative foundation for optimizing thermal models and designing cooling strategies in electric vehicle battery systems, thereby enhancing both safety and operational longevity.

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

CLC Number:

TM 911

Teng ZHANG, Guofeng CHANG. Thermal characterization and thermal consistency study of battery packs based on differences in monomer characteristic parameters[J]. Energy Storage Science and Technology, 2025, 14(8): 3194-3206.

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参数	数值
尺寸	148 mm×40 mm×91 mm
放电截止电压/V	2.8
充电截止电压/V	4.2
额定电压/V	3.75
额定容量/Ah	70
质量/g	1300
比热容/[J/(kg·K)]	968.3

连接方式	能量释放/Ah	平均发热率/W	最大发热率差异/W	发热量的最大标准差/W	放电后的平均温度/℃	放电后的最高温度/℃	最大温差/℃	温度的最大标准差/℃
并联	379.575	2.670	6.499	2.265	32.997	33.319	1.778	0.620
串联	366.042	2.601	1.261	0.475	32.567	32.898	0.767	0.275

连接方式	能量释放/Ah	平均发热率/W	最大发热率差异/W	发热量的最大标准差/W	放电后的平均温度/℃	放电后的最高温度/℃	最大温差/℃	温度的最大标准差/℃
并联	419.008	2.645	1.388	0.476	33.232	33.886	1.222	0.421
串联	415.38	2.585	1.133	0.431	32.780	33.102	0.670	0.233

连接方式	能量释放/Ah	平均发热率/W	最大发热率差异/W	发热量的最大标准差/W	放电后的平均温度/℃	放电后的最高温度/℃	最大温差/℃	温度的最大标准差/℃
并联	418.717	2.636	1.436	0.405	33.204	33.469	0.578	0.215
串联	420	2.640	0.262	0.097	33.233	33.467	0.512	0.190