Multi-objective optimization design for a double-direction liquid heating system-based Cell-to-Chassis battery module

Sub-zero temperature causes performance degradation, lifespan shortage, and even some safety issues of Li-ion battery cells, such as the internal short circuit. Preheating has become a critical issue for electric vehicle (EV) promotion in the high-latitude area or cold temperatures. To address this issue, a double-direction liquid heating-based Cell-to-Chassis (CTC) battery module is proposed for an extreme low-temperature environment (-40°C). Two cooling plates and the battery module are embedded in the chassis to reduce the component number. Besides, the volume energy density gets increased by 26.3%. The numerical calculation indicates that the proposed system is more efficient than the commonly utilized battery thermal management system (BTMS) in EVs. Moreover, the preheating effect with different heating intervals is compared; eight-minutes-preheating is proved to be more effective in preheating the battery module to 0°C with less energy consumption. Furthermore, a multi-objective optimization design is further carried out considering the heating rate, thermal safety, thermal uniformity, and energy cost. The impact of the mass flow rate in the mini-channels and the PTC heating film power are analysed through sensitivity analysis. Finally, the optimal design scheme is selected. The minimum, maximum, and volume average temperatures of the battery module are 273.2K, 296.7K, and 286.9K, respectively. Moreover, the temperature standard deviation is further reduced to 8.8K without much energy cost increment. This study guides for combing the efficient BTMS with the EV chassis for all-climate applications, especially with integrated preheating/cooling functions, which is feasible for the fast charging and cold environment applications, both the thermal management efficiency and the volume energy density can be effectively enhanced.