At present, the power battery used in electric vehicles is primarily a lithium-ion battery. The performance of lithium-ion power batteries is highly sensitive to temperature fluctuations. Due to the limited space available in the vehicle, a large number of batteries are required, and they are typically arranged closely together. This arrangement leads to challenges in managing heat distribution effectively.
In electric vehicles, the cooling system is generally divided into two main parts: one part cools the components of the drive system, such as the vehicle controller and DC/DC converter, while the other part focuses on cooling the power battery and the car charger. This article specifically explores the power battery cooling system.
Lithium-ion batteries generate heat during both charging and discharging processes. When the vehicle operates under various driving conditions—such as high speed, low speed, acceleration, or deceleration—the battery discharges at different rates, generating varying amounts of heat. Over time, this heat accumulation can lead to uneven temperature distribution within the battery pack, creating a complex and fluctuating operating environment.
The cooling performance of the power battery directly affects the efficiency, lifespan, and safety of the battery. As the battery generates heat during operation, its temperature rises, which in turn influences key parameters such as internal resistance, voltage, state of charge (SOC), available capacity, charge/discharge efficiency, and overall battery life.
To optimize the performance and longevity of the battery pack, it is essential to refine the battery structure, implement effective thermal management strategies, enhance heat dissipation mechanisms, and maintain a stable temperature environment for the battery.
**Main Cooling Schemes**
Different thermal management systems come with their own advantages and disadvantages. Factors such as component types, weight, system cost, and control methods influence the overall performance of the cooling system. When designing the thermal management system for a battery pack, it's crucial to consider not only the cooling requirements but also the vehicle’s performance and spatial constraints, along with the system’s stability and cost-effectiveness.
There are three primary cooling methods used in power battery systems: air cooling, liquid cooling, and heat pipe technology.
**1. Air Cooling**
Air cooling is currently the most widely used method due to its simplicity and ease of implementation. However, its cooling efficiency is relatively low. It involves using fans to circulate air through the battery pack, helping to dissipate heat. While this method is cost-effective, it may not be sufficient for high-performance applications where more efficient cooling is needed.
**2. Liquid Cooling**
Liquid cooling offers superior cooling performance and can evenly distribute temperature across the battery pack. However, it requires tight sealing of the battery module to prevent any leakage. Using conductive liquids like water can complicate the system and reduce cooling efficiency. Typically, a coolant such as ethylene glycol is circulated through pipes connected to each battery module, absorbing heat and transferring it to an external radiator via a fan.
**3. Heat Pipe Technology**
Heat pipe technology provides excellent heat dissipation and preheating capabilities for battery packs. It responds quickly and ensures uniform temperature distribution. Although still in the development stage, it is considered a promising future direction for battery cooling. However, layout and size limitations have prevented its widespread adoption in current vehicles.
From a practical standpoint, air cooling has long been dominant, especially in Japanese electric vehicles. However, as battery demands increase, liquid cooling is becoming the preferred choice for many manufacturers, including Tesla and BMW. In China, mainstream electric vehicle companies are also shifting toward liquid cooling systems. Looking ahead, liquid cooling is expected to become the mainstream solution.
**Key Components of Battery Pack Cooling Systems**
Each cooling method has specific components that support its function.
- **Air Cooling System**: Includes components such as cooling ducts, fans, and resistive wires.
- **Liquid Cooling System**: Consists of water-cooled pipes, cooling pumps, valves, and cooling plates.
The fan selection in an air cooling system is critical. It must provide adequate airflow based on the battery’s heat generation rate and meet temperature rise requirements. Similarly, the cooling plate in a liquid cooling system plays a vital role. It must meet pressure drop, flow consistency, bursting pressure, mechanical strength, vibration, and impact resistance requirements, as well as fit within the available space.
Many manufacturers supply these components, with traditional electrical companies often providing the main parts. Some battery management system and pack assembly companies also offer customized solutions tailored to specific needs.
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