Power battery is a systematic project. The quality of battery cells, group technology, management technology, temperature control technology, production process, etc. are all important factors that affect the stability and life of the battery. In particular, thermal management technology has a great impact on the car experience. Different thermal management schemes will bring very different practical effects. The following will introduce common battery pack thermal management solutions.

1. 4 common cooling methods
1. Natural cooling

The principle of natural cooling uses the natural convection of air to exchange heat, and the popular understanding is to rely on natural wind. This is a primary heat dissipation solution. The advantages are simple structure, low cost, and small footprint. However, the disadvantages are also obvious. The heat dissipation efficiency is low, and it cannot meet the cooling requirements of high-power charging and discharging. It is generally used to ease operating conditions and is very cost-effective. Sensitive two-wheeled electric motorcycles and some low-end cars.

2. Forced air cooling

Forced air cooling introduces air into the inside of the battery pack through a fan, and forces the cold air to flow over the surface of the battery cell and then discharge it, bringing the heat generated by the battery cell to the outside. The visual understanding is that compared with natural cooling, forced air cooling can actively create air flow, no longer "depending on the sky", and is more efficient than natural cooling, so it can better adapt to high-power charging and discharging. However, although the heat dissipation efficiency of forced air cooling has been greatly improved compared with natural cooling, it is still far less than liquid cooling. In addition, the demand for air inlet and outlet of the air cooling system makes it difficult for the airtightness of the battery system to reach a higher level.

3. Liquid cooling
The liquid cooling method mainly cools the battery system through the coolant. First, equipment such as condensers and compressors force the cooling liquid to cool down. After the low-temperature cooling liquid flows through the interior of the battery system and exchanges heat with the cells, it flows back to the heat exchanger for heat exchange with the low-temperature refrigerant. Heat is carried out of the battery system. Liquid cooling has higher heat dissipation efficiency than air cooling, and can meet the heat dissipation requirements of high-power charging and discharging. At the same time, liquid cooling heat dissipation is more uniform, and the temperature difference between cells is small, which is of great help to enhance the stability of the battery system and prolong its life. However, the liquid cooling system consumes a certain amount of energy during operation, and the cost of the liquid cooling system also increases slightly compared to the air cooling system.

4. Direct cooling
The structure of the direct cooling system is similar to the liquid cooling system, but the direct cooling will directly inject the refrigerant of the automobile air conditioning system into the battery pack, and the low temperature refrigerant can take away the heat inside the battery more quickly, and the heat dissipation efficiency is higher. However, the direct cooling system also has weaknesses. First, the system has high air tightness requirements and higher requirements for the manufacturing process. Second, the heat dissipation uniformity of the direct cooling system is not easy to control, and the temperature difference between the cells is at risk of being too large.

The most important point is that the direct cooling system cannot integrate the heating function, and an independent heating system (usually a heating film or PTC module) needs to be installed to deal with the low temperature in winter.

Among the above solutions, only the liquid cooling system can use the existing structure to realize the functions of cooling in summer and heating in winter, while ensuring the high sealing level of the battery system, so that the battery can quickly recover its activity.

In general, the liquid cooling solution can better meet the heat dissipation and temperature rise of the battery pack, thereby ensuring the stability of the high-power charging and discharging of the battery pack. It is relatively easy to implement in the production process, and achieves a relatively ideal performance and cost. balance.

1. Modular design

The standard battery box size is 710*275*200mm, the weight is 56kg, and the total energy is 7.88kWh. The standard battery box is built based on the modular design concept, and can be freely combined into power battery packs of different shapes, capacities and voltages to suit different models. When batteries with higher energy density are on the market, as long as the OEM needs to order the upgraded standard box replacement, it will quickly launch a remodeled model with a longer battery life, without modifying the vehicle structure and battery pack structure, saving the time and cost of upgrading. various costs.

2. Liquid cooling solution to cope with severe cold in winter and summer

The battery standard box adopts a liquid-cooled cooling scheme, and at the same time integrates two cold and heat exchange methods: weak cooling and strong cooling. When the temperature of the battery pack is below 45°C, use the radiator to cool down, which can save system energy consumption; when the temperature is above 45°C, use the compressor to cool down, quickly dissipate heat, and ensure that the battery system is at -40°C to 60°C It can work continuously and stably for a long time within the range.

As mentioned above, air cooling has low cooling efficiency and poor sealing reliability. The direct cooling method is a single cooling system, which cannot simultaneously achieve the function of heating the battery. The liquid cooling structure of the battery can not only realize the function of heat dissipation, but also realize the function of heating the battery.

In winter, the battery is affected by low temperature, the activity will be deteriorated, and the charging and discharging capacity will be greatly affected. The liquid cooling system of the battery can ensure the normal charging of the battery pack under extremely cold conditions (-30°C), and ensure the normal discharge of the battery in the low temperature environment, achieving zero power loss of the vehicle.

In addition, the fastest heating speed of liquid cooling can increase the temperature of the battery by 0.6 °C/min, while the fastest heating film, PTC and other methods are only 0.3 °C/min. Not only the heating speed is different, but the liquid cooling solution also heats more uniformly, which can control the temperature difference of the cell to 5°C, while the heating uniformity of the heating film and PTC is relatively poor, and the temperature difference of the cell is about 8-10°C.

Excessive temperature difference of the battery cells will make the electrochemical reaction rate inside the cells unbalanced, which will eventually lead to differences in the lifespan, capacity, and internal resistance of the cells, affecting the performance and life of the battery pack. The thermal management scheme of the battery can achieve a smaller temperature difference, which means longer battery life and lower repair rate.

When the liquid cooling system is working, it will heat or cool the coolant, which consumes a certain amount of energy. An adiabatic environment is created through the SMC shell, mica sheet, thermal insulation foam, etc., and the whole battery is sealed with an adiabatic environment, so as to reduce as much as possible. The influence of the external environment on the battery temperature, thus ensuring the ultra-low energy consumption of the thermal management system itself.

A little understanding of the image, a house is built for the battery core, and the thermal insulation effect is particularly good, so the "air conditioner" of the house is very power-saving. This means that the energy consumption of the whole vehicle is reduced, more electricity can be used to drive the vehicle, and the cruising range and user experience have been improved. ?

Summary: The battery pack is a systematic project, not a simple patchwork of accessories. It has high requirements for the manufacturer's design and manufacturing experience. The liquid-cooled product has been successfully applied to the super-power electric sports car K50, and it has been proved to have the ability to continuously charge and discharge high-power and stable performance, which further proves the excellent quality of its thermal management system.

As consumers become more and more aware of electric vehicles, battery packs with excellent liquid cooling and thermal management systems are increasingly becoming a must-have option for a high-quality electric vehicle.