Common Battery Thermal Management Technologies
for New Energy Vehicles
The cooling system of new energy vehicles generally consists of three parts: battery cooling circulation system, motor electronically controlled cooling circulation system, and air conditioning warm air circulation system. Different battery thermal management methods involve different parts numbers, structures, and layouts. Different types of thermal management systems are selected based on vehicle development costs, vehicle weight, and layout space requirements. Its main technical routes include the following five types.
1. Direct cooling type
Referred to as battery direct cooling technology, the direct cooling system has a built-in refrigeration evaporator inside the battery and is connected to the air conditioning system through pipelines. When the battery needs to be cooled, a compressor is used to send the compressed refrigerant into the evaporator inside the battery and then take away the battery. Internal heat achieves cooling effect. The system has the advantages of compact structure, good cooling effect, small number of parts (only one inlet and one outlet refrigeration pipeline is required), and light weight. However, the disadvantages of this system are that it cannot heat the battery under sub-zero low temperature conditions, the condensed water generated during the refrigeration process is not protected, and the temperature uniformity of the refrigerant is difficult to control. The refrigeration system has a short life and low reliability, and refrigerant leakage often occurs. Leakage, insufficient refrigeration capacity and other faults. This is the latest battery cooling technology with relatively low maturity. It has been applied in mass-produced models such as BYD and Tesla on the market. It is a major technical route in the future, as shown in Figure 1.
2. Radiator water cooling type
The radiator cooling circuit is an independent circuit, consisting of a radiator, an electronic water pump, a heater, etc., with antifreeze as the medium. The antifreeze comes out of the radiator, passes through the heater, then to the battery, and finally returns to the radiator. This cycle cools and heats the battery. The system has the advantages of simple structure, low cost and energy saving in low temperature environment all year round. However, the heat dissipation efficiency of this system is low, and the water temperature is high in high-temperature climate environments in summer, and it cannot meet the operating conditions in high-temperature environments, as shown in Figure 2.
3. Direct cooling water cooling type
This system integrates direct cooling and water cooling, and bridges the air conditioning system and water cooling system through the battery cooler Chiller (also called a heat exchanger). This system avoids the shortcomings of the first two cooling methods and is currently one of the most commonly used battery thermal management systems. The system has more components than the previous two. The system is more complex and requires a relatively large space for the arrangement of components. The compressor has a heavy load during operation, which consumes a lot of energy for the entire vehicle and is poorly economical. In addition, when part of the air-conditioning system fails, the cooling needs of the battery cannot be met to the maximum extent, see Figure 3.
4. Water-cooled hybrid type
This system is based on the direct cooling water cooling system and adds a radiator water cooling system. The two are arranged in parallel circuits. By controlling the solenoid valve, different circuits are used to cool the battery under different conditions. In low temperature environments, only the radiator water cooling system works. When in a high temperature environment, switch to direct cooling water cooling system to work. Under harsh working conditions, the two systems can work at the same time, and the battery can also obtain maximum cooling capacity, which can basically cover all use environments. This cooling system is extremely complex, has high cost, requires high vehicle layout space, has complex system control strategies, and poses a challenge to stability and reliability. This system is also used in most hybrid PHEV models on the market and has mature technology, as shown in Figure 4.
5. Air cooling type
This system directly leads the cold air from the passenger compartment cooling to the battery through the duct, and uses the cold air to air-cool the battery. The advantages of this system are simple structure, controllable cold air temperature and low system cost. However, it also has the disadvantages of the direct cooling system. The system has no heating function, and the condensed water generated on the battery surface is not easy to dry, and there is a risk of corrosion and contamination inside the battery. This type of thermal management method is generally not recommended, see Figure 5.
