Analysis of 3 Technical Routes for Power Battery Cooling Systems

 

　　The cooling performance of the power battery directly affects the efficiency of the battery, and also affects the battery life and safety. Because the battery itself generates a certain amount of heat during the charge and discharge process, which causes the temperature to rise, and the temperature increase will affect many characteristics of the battery, such as internal resistance, voltage, SOC, available capacity, charge and discharge efficiency, and battery life.

　　In electric vehicles, the cooling system is mainly divided into two parts: one is to cool the drive motor, vehicle controller and DC/DC converter of the power system, and the other is to cool the power battery and on-board charger of the power supply system. This article discusses power battery cooling systems.

 

 

　　Currently, power batteries for electric vehicles are lithium-ion batteries. The performance of lithium-ion power batteries is more sensitive to temperature changes; the available space for battery installation in vehicles is limited; the number of batteries required by vehicles is large; and the batteries are closely interconnected. When the vehicle is operating under various driving conditions—such as high-speed, low-speed, acceleration, and deceleration—the battery will discharge at different rates and generate large amounts of heat at varying heat-generation rates. Moreover, the cumulative effects of time and spatial factors will lead to uneven heat accumulation. As a result, the operating temperature of the battery pack becomes complex and highly variable.

　　The cooling performance of the power battery directly affects the efficiency of the battery, and also affects the battery life and safety. Because the battery itself generates a certain amount of heat during the charge and discharge process, which causes the temperature to rise, and the temperature increase will affect many characteristics of the battery, such as internal resistance, voltage, SOC, available capacity, charge and discharge efficiency, and battery life.

 

 

　　To ensure that the battery pack delivers optimal performance and longevity, it is necessary to optimize its structural design, implement thermal management, enhance heat dissipation capabilities, and maintain a controlled temperature environment for battery operation.

 

　　Main cooling scheme

　　Different thermal management systems, different types of components, different structures, different weights, different system costs, and different control methods result in varying system performances. When designing the type of battery pack thermal management system, it is necessary to consider the cooling performance requirements of the battery, combined with the performance of the vehicle and the size of the space, the stability and cost of the system are also factors to be considered.

 

　　Working instructions for different cooling systems

　　1. Air-cooled

　　The following cooling methods are used for electric vehicle battery packs both domestically and internationally: air cooling, liquid cooling, and heat pipe cooling. At present, the air cooling method is still the main method. Air cooling is relatively easy to achieve, but the cooling effect is not good.

 

Schematic diagram of a typical air cooling system

 

　　Liquid cooling

　　Liquid cooling offers a superior cooling effect and can ensure a uniform temperature distribution within the battery pack. However, liquid cooling places high demands on the tightness of the battery pack. If a conductive liquid such as water is used, both the liquid and the battery cells must be sealed with a water jacket. Moreover, body separation—not only increases the system's complexity but also reduces the cooling effect.

　　Generally, the cooling system is installed near the battery module. The principle is similar to the cooling principle of the air conditioner. The cooling system is connected to a single battery module through a pipe. The heat is taken away, the cooling system cools the glycol, and the excess heat is discharged to the outside through the fan, and the glycol is recycled into the battery module again to continue to absorb the heat emitted by the battery.

 

 

 

Schematic diagram of a typical liquid cooling system

 

　　3. Heat pipe technology

　　Heat pipe technology can meet the requirements of high-temperature heat dissipation and low-temperature preheating for battery packs. It features fast response and good temperature uniformity. Since the introduction of this new cooling method for battery packs, it has made considerable progress and has become a focal point of industrial research. However, due to limitations in layout and volume, there are currently no actual vehicles equipped with this technology in use.

 

Heat pipe technology working diagram

 

　　From the perspective of current electric vehicle power battery cooling methods, air cooling has always occupied a major position, especially Japanese electric vehicles, which basically use air cooling systems. As the application environment requires more and more batteries, liquid cooling has also become a priority solution for car companies, such as Tesla, BMW and other brands. China's mainstream electric passenger car companies have also begun to switch to liquid cooling systems. From the medium and long-term trend, liquid cooling will occupy the mainstream.

 

　　Main components of battery pack cooling system

　　Different cooling systems have corresponding cooling components: the main components of the air cooling system are fans, and the main components of the liquid cooling system are cooling plates.

　　Air cooling system components: cooling air duct, fan, resistance wire

　　The selection of the fan directly affects the cooling effect of the battery pack air cooling system. The selection requirements for the fan are as follows: determine the air flow based on the battery’s heat generation rate; meet the temperature rise requirements of each module; and select a fan that satisfies these requirements by considering both the system’s required air flow and the system’s pressure drop curve.

　　Liquid cooling system components: water-cooled pipes, cooling pumps, cooling valves, cooling plates

　　As one of the most critical components in the battery pack liquid cooling system, the cooling plate selection is very important. The selection of the cooling plate must meet the following requirements: the pressure drop of the cooling plate must meet the customer requirements; the consistency of the cooling water flow requirements; the burst pressure requirements; the mechanical requirements of the cooling plate; the cooling plate must pass the vibration and shock load tests; the cooling plate must meet tolerance requirements and space requirements.

　　There are many manufacturers of battery cooling system components, and most of the main components are provided by traditional electrical companies. At present, battery management system companies and PACK assembly companies also involve the production of customized products.

 

— From the list of cars