1. Background of the heat dissipation requirements for new energy vehicles

1. Power system overheating issue

• The core power system of new energy vehicles, such as battery packs and motors, generates a large amount of heat during operation. Taking the battery pack as an example, during the charging and discharging process, the chemical reaction inside the battery generates heat. Especially when charging quickly or discharging at high rates, the heat generated by the battery will be more obvious. For example,lithium-ion batteriesin fast charging state, the battery temperature may increase by 20 - 30 degrees Celsius. The motor temperature will also rise rapidly when it is operating under high load, such as when the car is driving at high speed or accelerating suddenly, due to the Joule heat generated by the current passing through the motor winding.

• For new energy vehicles with larger power, the power of the motor can reach 100 - 200kW. The heat generated under high-power operation will affect the performance and life of the motor if it cannot be dissipated in time. Moreover, the working environment temperature of the battery pack and motor has a great influence on their performance and safety. Excessive temperature may lead to serious safety problems such as battery thermal runaway.

2. Electronic device heat dissipation issues

• The interior of new energy vehicles is also equipped with a large number of electronic devices, such ason-board computers, power electronic devices (such as inverters), etc. These electronic devices also generate heat in the process of processing complex vehicle control signals and power conversion. For example, inverters, when converting direct current into alternating current to supply motors, will produce considerable heat due to the switching losses and conduction losses of power semiconductor devices (such as IGBT). Moreover, as the intelligence of automobiles continues to improve, the performance of these electronic devices is also continuously enhanced, and the heat they generate also increases accordingly.

2. Types and characteristics of thermal conductivity cooling materials

1. Liquid cooling heat dissipation material (coolant)

• Principle: The coolant circulates through the pipes, absorbing heat from the hot components (such as the battery pack, motor, etc.), and then transfers the heat to the radiator for dissipation. Coolant mainly uses its good heat capacity and thermal conductivity to achieve heat dissipation. Common coolants include ethylene glycol-water mixture, etc.

• Advantages: The heat dissipation efficiency of the liquid cooling system is high, and it can effectively control the temperature of the power system and electronic devices of new energy vehicles. For example, in the battery thermal management system of some high-performance new energy vehicles, liquid cooling can keep the battery pack temperature within the ideal range of 30 - 40 degrees Celsius. Moreover, the coolant can be flexibly distributed around the components that need to be cooled through the layout of a complex pipeline system, achieving centralized heat dissipation for multiple heat sources.

• Limitations: The liquid cooling system requires complex components such as pipes, pumps, and radiators, which increases the complexity and cost of the system. Moreover, there is a risk of leakage in the cooling fluid, and if the cooling fluid leaks onto critical components like the battery pack, it could cause safety hazards such as short circuits.

2. Phase change materials (PCM)

• Principle: Phase change materials undergo a phase change, such as from solid to liquid, when they reach a certain temperature. During this process, the phase change material absorbs a large amount of heat while the temperature remains relatively constant. When the temperature drops, it can change back from liquid to solid, releasing heat. For example, someparaffin-based phase change materials undergo a phase change around 30 - 40 degrees Celsius, which is suitable for temperature control of battery packs in new energy vehicles.

• Advantages: Phase change materials can automatically regulate the cooling process according to the temperature of the heat-generating components, without the need for external power devices. Arranging phase change materials around the battery pack can absorb heat when the battery temperature rises, effectively preventing the battery temperature from being too high. Its structure is relatively simple, and it can adapt well to the shape of components such as battery packs, filling the gaps between batteries and other positions without taking up too much extra space.

• Limitations: The thermal conductivity of phase change materials is relatively poor, and they may not be as efficient as liquid cooling systems in heat transfer. Moreover, the performance of phase change materials may decline after multiple phase changes, requiring regular maintenance or replacement.

3. Thermal grease silicone sheet

• Principle: Thermal grease is a high thermal conductivity elastic material that achieves heat transfer by closely adhering the heat-generating components and the heat-dissipating components, thereby reducing contact thermal resistance. It consists of a silicone rubber matrix and high-thermal conductivity fillers, with a thermal conductivity generally ranging from 1 - 5 W/(m・K).

• Advantages: The thermal grease sheet has good flexibility and elasticity, which can fill the irregular gaps between the heat-generating components and the heat sinks very well. For example, placing a thermal grease sheet between the power electronic devices and the heat sinks in new energy vehicles can ensure close contact between the two, improving the heat dissipation efficiency. It also has certain electrical insulation properties, which can prevent short circuits between electronic devices.

• Limitations: Its thermal conductivity is relatively low, and for some components with high heat generation density, using thermal grease alone may not meet the cooling requirements. Moreover, in high-temperature environments, the silicone pad may experience aging, deformation, and other issues, affecting its cooling performance.

Three, specific solutions for heat-conducting and heat-dissipating materials in new energy vehicles

1. Integrated application in the thermal management system of the battery

• System Description: In the thermal management system of the battery pack for new energy vehicles, a combination of liquid cooling and phase change materials is used. The cooling fluid pipes are arranged around the frame of the battery pack, and the majority of the heat generated by the battery is taken away by the circulating cooling fluid. At the same time, phase change materials are filled between the batterycells. When the cooling fluid cannot take away the heat in time, and the battery temperature locally increases, the phase change materials can absorb this heat to prevent the battery from overheating. For example, in the battery thermal management system of models such as the Tesla Model 3, through this combined application, the temperature fluctuation of the battery pack can be controlled within a smaller range, extending the service life of the battery and improving the safety of the battery.

• Advantages: This comprehensive application can fully play the advantages of liquid cooling and phase change materials. The liquid cooling system can handle the large amount of heat generated by the battery pack, providing a stable base heat dissipation; phase change materials can be used as an auxiliary heat dissipation means to deal with the situation of local temperature being too high, enhancing the reliability and safety of the battery thermal management system.

2. Motor cooling solutions

• Scheme Description: For the heat dissipation of the motor in new energy vehicles, on the one hand, a liquid cooling method can be used, where cooling fluid channels are set up inside or outside the motor's shell to directly cool the motor. On the other hand, thermal grease pads are filled between the stator and the shell of the motor to quickly conduct the heat generated inside the motor to the shell, and then the heat is taken away by the liquid cooling system. For example, some domestic new energy vehicle brands use this cooling scheme on their high-performance motors, which effectively reduces the temperature of the motor during high-load operation, improving the motor's working efficiency and reliability.

• Advantages: By combining liquid cooling and thermal grease, the temperature of the motor can be quickly and effectively reduced. The thermal grease ensures that the heat inside the motor is quickly conducted to the shell, while the liquid cooling system can dissipate the heat into the surrounding environment, ensuring that the motor maintains good working condition under various working conditions and reducing the risk of motor failure due to overheating.

3. Electronic device cooling strategy

• Scheme Description: For electronic devices in new energy vehicles, such as on-board computers and power electronic devices, the main approach is the combination of thermal grease and small liquid cooling heat sinks. A thermal grease is placed between the chip of the electronic device and the heat sink, which conducts the heat generated by the chip to the heat sink, and then the heat is dissipated through the small liquid cooling heat sink. For example, in the inverter of a new energy vehicle, the heat generated by the IGBT chip is conducted to the heat sink through the thermal grease, and then cooled by the liquid cooling system, which can effectively control the temperature of the electronic device and ensure its normal operation.

• Advantages: This cooling strategy can be flexibly adjusted according to the heat generation of electronic devices and spatial constraints. The thermal grease pad can adapt to the complex structure and small gaps inside the electronic device, ensuring the effective transfer of heat, and the small liquid cooling radiator can provide sufficient cooling capacity to meet the cooling needs of the electronic device, without occupying too much space inside the car.