Why do automotive power lithium battery packs require a cooling system?
The purpose of using a cooling system for automotive power lithium battery packs is to maintain the optimal operating temperature of the power battery by cooling or heating it, thereby improving its operational efficiency and extending its lifespan.
Analyze the basic principles of battery charging and discharging. Having studied physics, it is well known that battery charging is actually replenishing the electrons inside the battery, while discharge is consuming the electrons inside the battery. Both charging and discharging are accompanied by the violent movement of electrons, which results in thermal effects that cannot be avoided unless there is no electronic movement inside the battery. Therefore, if a lithium battery pack does not require a cooling system at all, it may require scientific principles beyond our understanding to support it.
Analyze from a technical perspective. Even with the support of new scientific principles and the discovery of new materials, in terms of technology, it is difficult for us to achieve the goal of not requiring a cooling system for power lithium battery packs. Because we have already spent decades developing lithium-ion batteries alone, and so far only a few companies have mastered the core technology, it is unlikely from this perspective.
At present, the thermal management of automotive power lithium battery pack systems can be divided into four categories: natural cooling, air cooling, liquid cooling, and direct cooling. Natural cooling is a passive thermal management method, while air cooling, liquid cooling, and direct current are active. The important difference between these three lies in the different heat exchange media.
1. Natural cooling
Natural cooling does not have additional devices for heat exchange. For example, BYD has adopted natural cooling on models such as Qin, Tang, Song, E6, and Tengshi that use LFp battery cells. It is understood that BYD will switch to liquid cooling in models that use ternary batteries in the future.
2. Air-cooled
Air cooling uses air as the heat exchange medium. There are two common types, the first one is called passive air cooling, which directly uses external air for heat exchange. The second type is active air cooling, which can heat or cool the external air in advance before entering the battery system. Many early Japanese and Korean electric vehicle models used air-cooled methods.
3. Liquid cooling
Liquid cooling uses antifreeze (such as ethylene glycol) as the heat exchange medium. There are usually multiple different heat exchange circuits in the method, such as the VOLT with radiator circuit, air conditioning circuit, and PTC circuit. The battery management system responds, adjusts, and switches according to the thermal management strategy.
4. Direct cooling
Direct cooling uses refrigerant as the heat exchange medium, which can absorb a large amount of heat during the gas-liquid phase change process. Compared with freezing liquid, the heat exchange efficiency can be increased by more than three times, and the heat inside the battery system can be carried away more quickly. The direct cooling system has the advantages of compact system, light weight, and good performance. However, this system is a dual evaporator system, with no battery heating, no condensate protection, difficult to control refrigerant temperature, and poor refrigerant system lifespan.
In summary, from the performance and overall structure of lithium battery packs, it is likely that future batteries will also struggle to break free from cooling systems. Therefore, the cooling system used in future lithium batteries will definitely be simpler but still indispensable than the current ones.
Summary: The cooling performance of power batteries directly affects their efficiency, as well as their lifespan and safety in use. Therefore, the safety performance requirements for the cooling system of lithium-ion battery packs for electric vehicles are very strict. When selecting the cooling system for electric vehicle power batteries, attention should be paid to both quality and protective devices.