At present, the majority of electric vehicles use lithium-ion batteries as their power source. The performance of these lithium-ion power batteries is highly sensitive to temperature fluctuations. Due to the limited space available in the vehicle, a large number of battery cells are required, and they are typically arranged closely together, which can lead to heat accumulation and uneven thermal distribution.
In electric vehicles, the cooling system is generally divided into two main parts: one is responsible for cooling components of the drive system, such as the vehicle controller and DC/DC converter, while the other focuses on cooling the power battery and the car charger. This article primarily discusses the cooling system for power batteries.
Lithium-ion batteries generate significant heat during operation, especially under varying driving conditions such as high speed, low speed, acceleration, or deceleration. The rate of heat generation varies depending on the discharge rate, and over time, this leads to uneven heat accumulation within the battery pack. As a result, the operating environment of the battery pack becomes complex and dynamic, with fluctuating temperatures that can affect performance and safety.
The cooling efficiency of the power battery directly influences the battery’s efficiency, lifespan, and overall safety. During charging and discharging, the battery generates heat, which affects key parameters like internal resistance, voltage, state of charge (SOC), available capacity, charge/discharge efficiency, and long-term durability. Therefore, maintaining an optimal temperature environment is essential for maximizing battery performance and longevity.
To enhance the performance and life of the battery pack, it is necessary to optimize its structural design, implement effective thermal management strategies, improve heat dissipation mechanisms, and maintain a stable temperature range for the battery.
**Main Cooling Schemes**
Different thermal management systems have various types of components, weights, costs, and control methods, leading to different levels of performance. When designing a thermal management system for a battery pack, it is important to consider the cooling requirements of the battery, along with the vehicle's performance and spatial constraints. System stability and cost are also critical factors in the selection process.
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 commonly used method due to its simplicity and ease of implementation. However, it is not the most efficient in terms of heat dissipation. Air cooling systems typically use fans to circulate air through the battery pack, helping to dissipate heat. While it is cost-effective, it may not be sufficient for high-performance applications.
**2. Liquid Cooling**
Liquid cooling offers better heat dissipation and can provide more uniform temperature distribution across the battery pack. It usually involves circulating a coolant, such as ethylene glycol, through channels around the battery modules. The system then transfers the heat to the outside via a radiator or fan. However, liquid cooling requires a sealed system, which increases complexity and cost. It is widely used in high-end EVs like Tesla and BMW.
**3. Heat Pipe Technology**
Heat pipe technology is a newer approach that allows for both high-temperature heat dissipation and low-temperature preheating. It offers fast response times and good temperature uniformity, making it a promising solution for future battery cooling systems. Despite its advantages, it is still in the development stage and has not yet been widely adopted in real-world vehicles due to layout and size limitations.
From a practical standpoint, air cooling remains dominant in many electric vehicles, especially in Japanese models. However, as the demand for higher performance and longer range increases, liquid cooling is becoming more prevalent among major automakers. In the long term, liquid cooling is expected to become the standard in the industry.
**Key Components of Battery Cooling Systems**
Each cooling method has specific components that contribute to its effectiveness:
- **Air Cooling System**: Includes fans, air ducts, and sometimes resistive heating elements.
- **Liquid Cooling System**: Consists of cooling plates, water-cooled pipes, pumps, valves, and heat exchangers.
For air cooling systems, the fan is a crucial component. Its selection must match the heat generation rate of the battery, ensure proper temperature regulation, and account for the system's pressure drop characteristics.
In liquid cooling systems, the cooling plate is one of the most critical components. It must meet strict requirements regarding pressure drop, flow consistency, mechanical strength, and vibration resistance. Additionally, it must pass rigorous testing to ensure reliability.
Many manufacturers produce components for battery cooling systems, with traditional electrical companies supplying most of the main parts. However, battery management system providers and PACK assembly companies are also beginning to offer customized solutions tailored to specific vehicle needs.
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