Power battery thermal management system
Power batteries are a key technology for new energy vehicles and are also an important factor in determining vehicle cost and cruising range. The thermal management system can be divided into active and passive thermal management from the perspective of thermal management controllability; and from the perspective of heat transfer medium, it can be divided into air cooling, liquid cooling and phase change thermal storage thermal management. The following will introduce in detail the "thermal management system of the three major heat transfer media of power batteries".
1. Thermal management using air as heat transfer medium
The heat transfer medium will greatly affect the performance and cost of the thermal management system. The principle of using air as the heat transfer medium is to directly introduce air and let it flow through the battery module to achieve the heat dissipation effect. This usually requires components such as fans and inlet and outlet ventilation. The sources of air intake generally include three forms: passive cooling/heating of outside air ventilation, passive cooling/heating of passenger cabin air ventilation, and active cooling/heating of outside or passenger cabin air.
The passive system structure does not require the establishment of a separate system and directly utilizes the existing environment. For example, if the battery is heated in winter, the hot air in the passenger compartment can be used. If the battery temperature is too high while the vehicle is driving and the passenger compartment air cooling effect is not good, the cold air from the outside can be sucked in to cool down. The active system is relatively complex and requires a separate system to provide cooling (heating) and control it according to the battery status. The system can be selected according to the battery usage requirements, but it will increase the vehicle cost and energy consumption.
2. Thermal management with liquid as heat transfer medium
This thermal management system uses liquid as the medium for heat transfer. It is necessary to establish a heat transfer connection between the module and the liquid medium, such as a water jacket, to conduct indirect heating and cooling in the form of convection and heat conduction. The heat transfer medium is often water, Ethylene glycol can also immerse the pole block in a dielectric liquid for direct heat transfer. Insulation measures are required to avoid short circuits.
Passive liquid cooling generally uses liquid-ambient air heat exchange and then introduces the cocoon into the battery for secondary heat exchange, while active liquid cooling achieves the first level through an engine coolant-liquid medium heat exchanger, or electric heating/thermal oil heating. Heating and primary cooling are achieved with passenger cabin air/air conditioning refrigerant-liquid medium.
The thermal management system using air and liquid as the medium requires fans, water pumps, heat exchangers, heaters, pipelines and other accessories, which makes the structure too large and complicated. It also consumes battery energy and reduces battery power. density and energy density.
The water-cooled battery cooling system uses coolant (50% water/50% ethylene glycol) to transfer the battery heat to the air-conditioning refrigerant system through the battery cooler and to the environment through the condenser. The battery inlet water temperature is cooled by the battery It is easy to reach a lower temperature after heat exchange, and the battery can be adjusted to operate within a suitable operating temperature range. The main components of the refrigerant system include: condenser, electric compressor, evaporator, expansion valve with cut-off valve, battery cooler (expansion valve with cut-off valve) and air conditioning pipes, etc.; the cooling water path includes: electric water pump, battery (including cooling plate), battery cooler, water pipes, expansion tank and other accessories.
3. Phase change regenerative thermal management
The principle of phase change material PCM to cool the battery is: when the battery is discharged with high current, the phase change material absorbs the heat released by the battery, and its own phase change causes the battery temperature to drop rapidly. This process is that the system stores heat in the form of phase change heat in the phase change material PCM. When the battery is being charged, especially in colder weather conditions (the atmospheric temperature is much lower than the phase change temperature PCT), the PCM can discharge heat to the environment.
The use of phase change materials in battery thermal management systems has the advantage of not requiring moving parts or consuming additional energy from the battery. Phase change materials with high phase change latent heat and thermal conductivity are used in the thermal management system of battery packs to effectively absorb the heat released during charging and discharging, reduce battery temperature rise, and ensure that the battery operates at normal temperatures. It can keep battery performance stable before and after high current cycling. Composite PCM is made by adding substances with high thermal conductivity to paraffin wax, which helps to improve the overall performance of the material.
