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The power battery serves as the energy source for electric vehicles. During charging and discharging, the battery generates heat, which can cause a rise in temperature. This temperature increase affects various operational characteristics of the battery, such as internal resistance, voltage, state of charge (SOC), available capacity, charge and discharge efficiency, and overall battery life. Therefore, effective thermal management is essential to ensure optimal performance, longevity, and safety of the battery system.
This article covers the following topics:
01. Necessity of Power Battery Thermal Management
02. Classification and Introduction of Thermal Management Systems
03. Design Process of Thermal Management Systems
04. Key Technologies in the Design Process
05. Performance Evaluation of Thermal Management Systems
The thermal behavior of batteries significantly impacts the performance and cycle life of electric vehicles. Hence, implementing proper thermal management is crucial to enhance battery performance, extend its lifespan, and improve the vehicle's range. In the following sections, we will explore battery thermal management systems, their design process, component types, and performance evaluation.
**01. Necessity of Power Battery Thermal Management**
1. **Heat Generation in Batteries**
During charging and discharging, current flows through the battery, generating heat due to internal resistance. Additionally, electrochemical reactions within the battery also contribute to heat generation.
2. **Impact of Temperature on Battery Life**
Elevated temperatures affect both calendar life and cycle life. For example, at 55°C, a battery may lose 20% of its capacity after just 272 days, while at 23°C, it retains 80% of its capacity after 6,238 days. A temperature increase of 32°C can reduce calendar life by over 95%.
Similarly, higher temperatures reduce cycle life. At 35°C, a battery may only deliver 163kWh compared to 300kWh at 25°C. A 10°C increase can cut cycle life by nearly 50%. These findings emphasize the critical need for thermal management to maintain consistent battery performance and longevity.
**02. Classification and Introduction of Thermal Management Systems**
Thermal management systems vary in design, components, weight, cost, and control methods. The five main categories are:
1. **Direct Cooling System**
Compact and efficient, but lacks heating and condensate protection, with limited refrigerant control.
2. **Low-Temperature Radiator Cooling System**
Simple and cost-effective, but has poor cooling performance in high-temperature environments.
3. **Direct Water Cooling System**
Offers good cooling performance and wide application, but is more complex and consumes more energy.
4. **Air-Water Hybrid Cooling System**
Combines air and water cooling for better efficiency and energy savings, though it is more expensive and complex.
5. **Direct Air Cooling System**
Uses ambient air for cooling, simple and low-cost, but not suitable for all battery types and may lead to contamination risks.
**03. Thermal Management System Design Process**
The design of a thermal management system should align with the development of the battery pack. It involves multiple stages, including sample testing, validation, and optimization. The design process typically includes seven key steps: system modeling, thermal field analysis, component selection, simulation, testing, and performance evaluation.
**04. Key Technologies in the Design Process**
1. **Determining Optimal Operating Temperature Range**
Different battery chemistries have different optimal temperature ranges. Lead-acid batteries perform best between 35–40°C, nickel-hydrogen batteries between 0–40°C, and lithium-ion batteries between -20–75°C.
2. **Thermal Field Calculation and Temperature Prediction**
Mathematical models help predict internal battery temperatures, using equations involving density, specific heat, thermal conductivity, and heat generation rate.
3. **Heat Rate Analysis**
Heat generation occurs during both charging and discharging, with different sources depending on the phase of the process.
4. **Heat Dissipation Structure Design**
Ensuring even heat distribution among battery modules is critical to avoid overheating and maintain performance.
5. **Fan and Temperature Sensor Placement**
Choosing the right fan type and positioning temperature sensors effectively improves system efficiency and accuracy.
**05. Thermal Management System Performance Evaluation**
Simulation tools like FloEFD and Flowmaster are widely used to evaluate thermal management systems. They help analyze pressure drop, cooling efficiency, and optimize airflow and water flow.
Examples include simulations for hybrid vehicles, direct air-cooled battery packs, and air-water hybrid systems. These simulations provide insights into thermal performance under different conditions, supporting system design and control strategy optimization.
In conclusion, battery temperature directly affects safety and performance. Proper thermal management is a critical aspect of battery system design, ensuring reliability, efficiency, and long-term durability.
September 27, 2025