Exploration of using phase change material for thermal management of Electric Vehicle Battery

Abstract

Battery thermal management (BTM) has been considered as one of the most important components in battery management system (BMS), as the thermal performance could heavily influence the safety and the performance of the battery and thus effect on the electric vehicle (EV) or hybrid electric vehicle (HEV). Some widely explored BTM systems includes forced air-cooling, direct/indirect fluid-cooling, and heat pipe (HP) systems. The forced air-cooling suffers from the low heat exchange efficiency between the air and the battery wall, while the direct/indirect fluid-cooling method takes the disadvantage of the extensive overall volume with the requirement of some other accessories such as the pump. Besides, HP systems have the limitation as it needs complex system layouts and thus high system weight.
Phase change material (PCM) BTM system has attracted increasing interest as the latent heat could be normally greater than the sensible heat (cooling) those in traditional cooling systems. Moreover, PCM BTM system could work independely without supportive energy or extra accessories, which enables itselt to be employed flexibly in the EV and HEV. However, PCM cooling method faces the issue of leakage, which limits its application in the EV battery packs. The form-stable PCM (FSPCM) and micro-encapsulated PCM (MPCM) slurry then comes to the solution. The conventional PCM with the potential to leak in the battery pack could be embeded in the supoorting matrix to form the FSPCM, or micro-encapsulated in the shell to form the MPCM. Both methods provides surroundings to hold the phase transition process inside and prohibited liquid-phase PCM from flowing into the outter.
As the research which employed FSPCM or MPCM slurry methodologies in BTM systems was very limited, in this PhD project, FSPCM and MPCM slurry were utilized in BTM systems to evaluate their perofmance in BTM. It was expected to improve the existed BTM technologies, and thus enhance the battery safety and performance for EV, HEV or even further related applications.
The methodologies accessible for BTM used in EV or HEV were reviewed in Chapter. 2. The development histories and the features were introduced towards various measures, with the emphasis on PCM BTM, especially FSPCM and MPCM. The scientific gap was therefore pointed out.
A numerical model of the FSPCM BTM was established in Chapter. 3, using MATLAB. The BTM performance was compared in four scenarios, and the optimal one was demonstrated to be the coupled FSPCM and air-cooling BTM system. With higher EG mass fraction, the increase rate of Tcor was observed to be reduced. When the EG mass fraction was 4.6 wt%, Tcor at tC was 317.7 K, 5.2 K lower than 322.9 K (without any EG additives). The thickness of FSPCM should be carefully selected according to the heat generated by the target battery pakage. Comprehensively considering the capital cost of the FSPCM BTM or the size of that system, 0.06 could be the competitive candidate among all.
The experimental investigation of BTM system performance has been conducted in Chapter. 4. Either MPCM slurry or water worked as the coolant to accompanish the BTM system. Their performance were separately discussed towards different working conditions (battery pack charging rates, and C-rates). The optimal working condition for MPCM slurry integrated BTM system was when the charge rate was 2C, as the group using C-rate of 2C spend the longest time of MPCM slurry in the melting range. In thiscondition ∆Tcor was 26.87 °C
Modelling work of BTM system has also been done in Chapter. 5 utilizing ANSYS. The experimented BTM system was modelled with the cooling fluid alternatively switched between MPCM slurry and water, while the cooling module basement made by aluminium or FSPCM discussed in Chapter. 3. High MPCM mass ratio has limited effect on BTM system performance using Al-basement, even though it can slightly enhance the battery cooling performance using FSPCM-basement, in the confined simulation conditions. FSPCM-basement was more promising for a lower battery temperature, compared to Al-basement. The heat transfer between the battery and the coolant was enhanced by the application of FSPCM-basement. The Tcor reduction by substituting aluminium with FSPCM is 0.94%, 0.25%, and 0.01%, respectively, with C-rate ranging from 10C to 3C.
In a conclusion, the BTM integrated with FSPCM and PCM showed the potential to be a high-performance BTM for battery packages used in EV/HEV.