In the current context of transition from the powertrains of cars equipped with internal combustion engines to powertrains based on electricity, there is a need to intensify studies and research related to the command-and-control systems of electric vehicles. One of the important systems in the construction of an electric vehicle is the thermal management system of the battery with the role of optimizing the operation of the battery in terms of performance and life.
Air cooling represents the most easily applicable solution for the thermal management of batteries. However, the low specific heat of air still is a major concern when considering its application in full-size battery packs. A possible solution could be the use of active cooling and heating, using an evaporator or heater core. This would allow a reduced dependency on ambient conditions, an increased control over the inlet temperature in the battery pack and therefore a more efficient management of the temperatures inside the pack. Although such a method would increase the heat transfer, the occupied large volume still represents a significant disadvantage. The inlet and outlet scheme and the air flow configuration are also promising research directions, with numerous possible combinations. However, the possibility of implementing these schemes in a full-size battery pack should also be investigated, considering the need to implement the required inlet and outlet channels in the tight package of a vehicle. Regarding the uneven temperature distribution of air cooling, this can be reduced by using air flow channels with variable widths or by distribution pipes.
The large use of prismatic and pouch batteries in commercial vehicles means that liquid cooling plates are one of the most implemented cooling systems in electric vehicles, due to their good heat capacity and compact arrangement. Most research studies focus on various parameters regarding heat transfer and pressure drop, but only a few consider the uneven heat generation in the batteries, which is even more significant for the larger prismatic and pouch batteries. Therefore, more attention in future studies should be accorded to the possibility of implementing bidirectional or reciprocating liquid flows, considering the local heat generation, therefore improving the temperature distribution. In the presented study, examples of improving the temperature uniformity offered by cooling plates are presented using double-layered plates and a better mass distribution in the channels. The heat transfer capacity of conventional liquid cooling systems can further be enhanced using PCM emulsions or liquid metal. For cylindrical batteries, the poor adaptability to indirect liquid cooling is represented by the use of wavy channels, half helical ducts or conduction elements, which significantly increase complexity and add weight to the system.
Adapting the existing refrigerant circuit of the vehicles to serve also for the thermal management of batteries is a concept with a relatively high probability of practical application. The presented studies clearly show the potential of such systems, having a high heat transfer capacity, a capability to cool below ambient temperature and the possibility of heating. Despite these advantages, there are no mentioned studies to analyze the sizing of such a system for a full-size battery pack, nor the necessary changes to the existing air conditioning system to cope with the additional thermal load of the battery. More effort should be directed towards the development of a large-scale system, with precise control algorithms for cabin comfort, battery maximum temperature and temperature uniformity.
The main disadvantages of pure PCMs, namely the low thermal conductivity and leakage problems can be tackled by adding other materials such as EG, AlN, nanosilica, copper mesh foam and others, to form CPCMs. Although the enhancement of pure PCM with additional materials in different concentrations is a promising research direction, the preparation processes are very laborious, as well as time and energy consuming. It could be of interest by how much the preparation of large quantities of CPCM increases the overall costs of full-size battery packs. Moreover, in the case of pouring hot, melted CPCM directly around the batteries, further investigations are needed regarding the possible negative effects on Li-ion batteries.