Summary
Cell‐to‐pack (CTP) structure has been proposed for electric vehicles (EVs). However, massive heat will be generated under fast charging. To address the temperature control and thermal uniformity issues of CTP module under fast charging, experiments and computational fluid dynamics (CFD) analysis are carried out for a bottom liquid cooling plate based–CTP battery module. The impact of the channel height, channel width, coolant flow rate, and coolant temperature on the temperature and temperature difference are analyzed. A liquid cooling control method of exchanging the coolant inlet and outlet is proposed to optimize the temperature uniformity. Besides, the temperature uniformity enhancement by this control method at different intervals is compared. Results indicate that the flow rate and temperature positively affect the battery temperature; the maximum temperature can be reduced by 10.93% and 15.12%, respectively, under the same operations. However, the coolant temperature increment increases the maximum temperature difference by about 41.58%. Reversing flow enhances the cooling effect of conventional unidirectional flow of the CTP battery module under fast charging, especially for the thermal uniformity, which provides guidance for the battery thermal management system (BTMS) control under fast charging.
A new model for simulating battery temperature changes from the lower surface to the upper surface is proposed. The cell model is established with experimental calibration. Simultaneously, the Cell-to-Pack model is established through experimental benchmarking. In addition, the thermal properties of Cell-to-Pack and an ordinary battery pack that has an enclosure on the basis were compared under four different working conditions. The results indicate that adding an enclosure to the Cell-to-Pack has little effect on the thermal performance of the battery pack. Adding an enclosure to the Cell-to-Pack hardly improve the temperature uniformity of the battery under cooling conditions; the temperature difference between the upper and lower surfaces of the batteries at both ends of the module drops by approximately 0.5°C, while the central temperature difference is basically unchanged. Compared with fast charging without cooling, the battery temperature dropped by more than 12°C under the fast charge condition with cooling. More importantly, the specific energy and packaging efficiency of the battery dropped from 160.27Wh·kg−1 and 73.1% to 148.72 Wh·kg−1 and 67.8%, respectively, after the Cell-to-Pack was added with an enclosure.
Thermal runaway propagation (TRP) is a primary safety issue in lithium-ion battery (LIB) applications, and the use of a thermal barrier is considered to be a promising solution for TRP prevention. However, the operating conditions of the battery are extremely complicated, such as fast charging, low-temperature heating and thermal runaway. To date, there is no consistent answer as to how to choose the appropriate thermal barrier for such a complicated working environment. In this study, the characteristics of hydrogel based on sodium polyacrylate are explored, and the impact of thermal barrier area on TRP is investigated through experiments. Due to the prismatic battery structure, thermal barriers placed between cells are designed with different areas (148 × 98 mm, 128 × 88 mm, and 108 × 78 mm). The results indicate that test 1 without a placed thermal barrier quickly completes the TRP process, and the thermal runaway (TR) behavior is more violent. With a thermal barrier that does not have full area coverage placed between cells (test 2 and test 3), the propagation time is prolonged, but TRP still occurs. Compared with test 1, the triggered temperature of T2 F (the front surface of cell 2) is reduced by 207.6 °C and 295.2 °C, respectively. The complete area coverage thermal barrier successfully prevents TRP, and the T2 F of cell 2 only reaches 145.4 °C under the phase change by the hydrogel. This study may suggest a safety design for battery modules and prevent propagation among batteries.
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