Thermal Management Technology
Battery Thermal Management
Battery thermal management is a key component of the thermal management system of electric vehicles. Its main goal is to ensure that the battery pack maintains a suitable operating temperature under various operating conditions to ensure battery performance, safety and service life. Battery thermal management mainly includes two aspects: heat dissipation and heating. The following will elaborate on the different technical paths to achieve these two functions.
1.Battery heat dissipation
1) Air cooling. Air cooling is a relatively simple and low-cost heat dissipation method. It removes the heat generated by the battery through natural convection or by installing a fan to force air flow. The air cooling system mainly relies on the heat sink on the surface of the battery pack for heat exchange, which is suitable for scenarios with low power density requirements or moderate ambient temperature. However, due to the small specific heat capacity of air, the heat exchange efficiency is relatively limited, and the rapid cooling ability for high-power and high-energy density batteries is weak.
2) Liquid cooling. The liquid cooling solution uses coolant (such as water, ethylene glycol solution, etc.) as the heat transfer medium, which is in direct contact with the battery through a circulation pipe to achieve efficient heat conduction. The liquid cooling system can accurately control the battery temperature, especially for high-performance electric vehicles. While effectively preventing the battery from overheating, it ensures that the battery temperature is evenly distributed, thereby improving the battery life and overall performance. However, liquid cooling has certain limitations. The liquid cooling system is more complex, there is a risk of liquid leakage, there are certain requirements for the corrosion resistance of the material, and the maintenance cost is increased.
3) Phase Change Material (PCM) heat dissipation. Phase change materials can absorb a large amount of latent heat during the solid-liquid phase transition process, thereby achieving a good heat dissipation effect. When applied to battery thermal management, PCM can be wrapped around the battery or embedded in the battery module to absorb heat when the battery temperature rises, playing a role in slow heat release. The advantage of PCM heat dissipation is its constant temperature characteristics, which prevents the battery temperature from rising suddenly, but the disadvantages are also relatively obvious. Its thermal conductivity is relatively poor, the response speed is slow, and the material cost is high.
4) Heat pipe heat dissipation. Heat pipes can transfer heat by using the phase change process of the working fluid without external energy input to achieve efficient thermal conductivity. In battery thermal management applications, heat pipes can quickly transfer heat from local hot spots and improve the temperature consistency of the entire battery pack. Heat pipes have the advantages of high heat transfer efficiency, small size, and light weight, but their structure is complex, the manufacturing cost is relatively high, and attention should be paid to designing a suitable condensation end to ensure heat dissipation efficiency.
5) Direct cooling heat dissipation. Direct cooling mainly refers to the cooling medium (usually liquid) flowing directly through the battery module or battery cell to effectively control the operating temperature of the battery. This design allows the battery surface to dissipate heat quickly, which is particularly suitable for high temperature and high power demand occasions. However, direct cooling has extremely high requirements for sealing, and once the coolant leaks, it may cause serious safety hazards.
2. Battery heating
1) PTC heating. The positive temperature coefficient (PTC) heater is based on the positive temperature coefficient effect, that is, the resistance increases with the increase of temperature. Therefore, it can provide stable heat output in low temperature environment while automatically limiting its own temperature from being too high. PTC heating is widely used in electric vehicles for comfort, such as seat heating and auxiliary heating of the in-vehicle air conditioning system. Due to its self-regulating characteristics, it can provide stable and efficient heating effects while avoiding problems caused by overheating. It is an efficient heating technology. However, PTC heating is electric heating, which will increase the total energy consumption of electric vehicles and reduce the driving range.
2) Heat pump heating. The heat pump air conditioning system absorbs low-temperature heat from the external environment through the reverse Carnot cycle, and transfers it to the battery and cabin through the process of compressing and releasing heat. Compared with traditional PTC heating methods, heat pumps are more energy efficient in low-temperature environments and help maintain vehicle performance. However, the design and operation of heat pump systems are more complex, especially in extreme low-temperature conditions, where their performance will decline. For this reason, some studies have proposed innovative technologies such as air injection and dual-source heat pumps to optimize heat pump performance at low ambient temperatures.
