The power battery is the core of an electric vehicle, requiring it to withstand high temperatures, water, and freezing temperatures. When an electric vehicle stops moving, the first thought is often that the "core" (battery) is faulty. But can the power battery withstand the high temperatures of summer?
How to dissipate heat from the power battery of an electric vehicle? Power batteries operate at high currents, generating significant heat. Simultaneously, the battery pack is in a relatively enclosed environment, leading to an increase in battery temperature. This is due to the electrolyte within the lithium battery; the electrolyte plays a crucial role in charge conduction, and a battery without an electrolyte cannot be charged or discharged.
Lithium-ion batteries are mostly composed of flammable and volatile non-aqueous electrolytes. This composition system has higher specific energy and voltage output compared to batteries with aqueous electrolytes, meeting users' higher energy demands. However, because non-aqueous electrolytes are themselves flammable and volatile, they permeate the inside of the battery and become a source of combustion.
Therefore, the operating temperature of both of the aforementioned battery materials must not exceed 60℃. However, the outdoor temperature is now close to 40℃, and the batteries themselves generate a lot of heat, which will cause the operating temperature of the batteries to rise. If thermal runaway occurs, the situation will be extremely dangerous. To avoid turning the batteries into "grills," heat dissipation is particularly important.
There are two types of heat dissipation for power battery packs: active and passive, with significant differences in efficiency. Passive systems require lower costs and simpler measures. Active systems are more complex in structure and require greater additional power, but their thermal management is more effective. Different thermal interface materials result in different heat dissipation effects; air cooling and liquid cooling each have their advantages and disadvantages.
The main advantages of using gas (air) as a heat transfer medium for thermal conductivity and insulation are: simple structure, light weight, effective ventilation when harmful gases are generated, and low cost; the disadvantages are: low heat transfer coefficient between the gas and the battery wall, slow cooling rate, and low efficiency. It is currently widely used.
The main advantages of using liquid as a heat transfer medium are: high heat transfer coefficient between the liquid and the battery wall, and fast cooling speed; the disadvantages are: high sealing requirements, relatively large mass, complex maintenance and repair, requiring components such as water jackets and heat exchangers, resulting in a relatively complex structure. In practical electric bus applications, due to the large capacity and volume of the battery packs, the power density is relatively low, so air cooling is often used. However, for battery packs in ordinary passenger cars, the power density is much higher. Correspondingly, the requirements for heat dissipation are also higher, so water cooling is more common.
Different battery pack structures require different sensors depending on the temperature measurement points and requirements. Temperature sensors are placed in the most representative locations with the greatest temperature variations, such as air inlets/outlets and the central area of the battery pack. This is especially important at the highest and lowest temperatures, and in areas where heat accumulates significantly in the center of the battery pack. This helps to maintain the battery temperature in a relatively safe environment, preventing overheating and overcooling from posing a danger to the battery.
