Introduction of new energy power battery cooling principle
Power battery is an important core component of new energy vehicles. It is not only expensive, but also determines the cost of building new energy vehicles, and also determines the driving range of new energy vehicles, which affects consumers’ car experience.
The power battery used in new energy vehicles is a rechargeable chemical battery. Its charging and discharging process is actually a chemical reaction process. Therefore, during the charging and discharging process, the power battery will be released with the intensity of the chemical reaction. out a certain amount of heat. We know that the negative electrode, electrolyte and battery separator inside the power battery will burn, and the ignition point of the electrolyte is very low. Therefore, if the huge power battery pack of new energy vehicles does not do a good job of thermal management, it will not only be easy to use The battery is damaged, and it is very easy to cause a burning accident.
The power battery pack is composed of many cells. When battery manufacturers produce power batteries, they often use the characteristics of batteries to dissipate heat. For example, the gap between cylindrical batteries is large, and the surface area of square batteries is large. In addition, battery manufacturers will also dissipate heat from the power battery in the following ways.
Method 1: Natural heat dissipation.
It is to use a high thermal conductivity material to make a heat sink (the thermal conductive silicone sheet with a back silicone cloth has a wide range of applications), which is connected to the power battery pack to take away the heat generated by the battery when it is working, and naturally dissipate it into the air. This cooling method is relatively passive, and the cooling effect is not very good, but the cost is lower.
Method 2: Air cooling for heat dissipation.
On the basis of natural heat dissipation, a fan with heat sink is installed to increase the heat dissipation area and air circulation speed, so that the heat inside the power battery pack can be quickly dissipated.
- A cooling fan is installed at one end of the power battery pack, and ventilation holes are left at the other end to accelerate the flow of air between the gaps of the cells and take away the high heat generated by the cells during operation;
- A thermally conductive silicone sheet is added to the top and bottom of the electrode, so that the heat that is not easily dissipated at both ends is conducted on the metal shell through the thermally conductive silicone pad to dissipate heat. protection.
Method 3: Liquid cooling for heat dissipation.
It is to add a set of liquid cooling radiator to the power battery pack and form a loop. After the heat generated by the battery is transferred to the liquid in the radiator, the liquid generates convection due to the heat transfer, so that the liquid can flow by itself in the circuit, thereby carrying heat.
- The heat of the cell is transferred to the liquid cooling tube through the thermal conductive silicone sheet, and the heat is taken away by the principle of thermal expansion and contraction of the cold liquid, so that the temperature of the entire power battery pack is unified, and the strong specific heat capacity of the cold liquid absorbs the work of the cell. The heat generated during the operation makes the entire battery pack operate within a reliable temperature;
- The thermally conductive silicone sheet has good high resilience and insulation performance, which can avoid the problem of vibration, friction and damage between the cells and the hidden danger of short circuit between the cells. It is a good auxiliary material for the water cooling scheme.
Method 4: Refrigeration and heat dissipation.
It is to use the process of gas-liquid change of the refrigerant as a heat exchange medium to rapidly decrease the temperature of the power battery. This method has the best cooling effect and the highest cost.
At present, the power batteries of new energy vehicles are mostly air-cooled and liquid-cooled.
The power battery has a large working current and a large amount of heat. At the same time, the battery pack is in a relatively closed environment, which will cause the temperature of the battery to rise. There are two types of power battery cooling, active and passive, and there is a big difference in efficiency between the two. Passive systems require lower costs and simpler measures. Active systems are more complex and require more additional power, but their thermal management is more efficient.
Different heat transfer media have different heat dissipation effects, and air cooling and liquid cooling have their own advantages and disadvantages.
The main features of using thermal conductive silica gel sheet as a medium for conducting heat: install the thermal conductive silica gel sheet for power battery between the battery cell and the battery cell, between the battery module and the battery module, and the battery module and the casing. The sheet has the characteristics of high thermal conductivity, insulation, shock absorption, tear resistance, good caulking ability, and a service life of more than 10 years. It can quickly transmit the heat generated by the heat source through the thermal conductive silicone sheet.
The main advantages of using gas (air) as the heat transfer medium are: simple structure, light weight, effective ventilation when harmful gases are generated, and low cost; disadvantages are: low heat transfer coefficient with the battery wall, slow cooling speed ,low efficiency. There are currently many applications.
The main advantages of using liquid as the heat transfer medium are: high heat transfer coefficient with the power battery wall and fast cooling speed; disadvantages are: high sealing requirements, relatively large quality, complicated repair and maintenance, need water jacket, Components such as heat exchangers are relatively complex in structure.