New energy industry solutions

The importance of thermal management systems

The heat-related issues of a battery are key factors in determining its performance, safety, longevity, and cost of use. First, the temperature level of a lithium-ion battery directly affects the energy and power performance of its use. At lower temperatures, the available capacity of the battery will rapidly decay. Charging the battery at too low a temperature (such as below 0 °C) may cause an instantaneous voltage overcharge, causing internal lithium and causing a short circuit. . Secondly, the heat related problems of lithium ion batteries directly affect the safety of the battery. Defects in the manufacturing process or improper operation during use may cause local overheating of the battery, which in turn may cause a chain exothermic reaction, eventually causing serious thermal runaway events such as smoke, fire or even explosion, threatening the life of the vehicle occupants. Safety. In addition, the working or storage temperature of a lithium ion battery affects its service life. The proper temperature of the battery is between 10 and 30 ° C. Too high or too low temperature will cause a rapid decay of battery life. The large size of the power battery makes the ratio of surface area to volume relatively small, the internal heat of the battery is not easy to be dissipated, and the internal temperature unevenness and local temperature rise are more likely to occur, thereby further accelerating battery attenuation, shortening battery life, and increasing users. Total cost of ownership.

The battery thermal management system is one of the key technologies to deal with the heat related problems of the battery and to ensure the performance, safety and life of the power battery. The main functions of the thermal management system include: 1) effective heat dissipation when the battery temperature is high to prevent thermal runaway accidents; 2) preheating when the battery temperature is low, increasing the battery temperature, ensuring charging and discharging performance at low temperatures And safety; 3) reduce the temperature difference in the battery pack, inhibit the formation of the local hot zone, prevent the battery from decaying too fast at the high temperature position, and reduce the overall life of the battery pack.

THE HEAT MANAGEMENT SYSTEM OF TESLA ROADSTER BATTERY

The vehicle battery pack consists of a 6831 section 18650 lithium-ion battery, in which each 69 sections are connected in parallel as a brick, and then 9 sets are connected in series as a sheet, and finally 11 layers are stacked in series. The coolant in the battery thermal management system is a mixture of 50% water and 50% ethylene glycol.

The cooling duct is arranged in a zigzag between the batteries, and the coolant flows inside the duct to remove the heat generated by the battery. The inside of the cooling pipe is divided into four holes. In order to prevent the temperature from gradually rising during the flow of the coolant, the heat dissipation capability of the end is not good. The heat management system adopts a flow field design of two-way flow, and both ends of the cooling pipe are both liquid. The mouth is also the liquid outlet, as shown in Figure 1(d). Materials that are electrically insulated but have good thermal conductivity between batteries and pipes (such as Stycast 2850/ct) are used to: 1) convert the contact between the battery and the heat pipe from line contact to surface contact; 2) It is beneficial to increase the temperature uniformity between the cells; 3) It is beneficial to increase the overall heat capacity of the battery pack, thereby reducing the overall average temperature.

Through the above thermal management system, the temperature difference of each unit cell in the Roadster battery pack is controlled within ±2 °C. A June 2013 report showed that after driving 100,000 miles, the capacity of the Roadster battery pack can still be maintained at 80% to 85% of the initial capacity, and the capacity reduction is only significantly related to the mileage, and the ambient temperature. The relationship between car age is not obvious. The achievement of the above results relies on the strong support of the battery thermal management system.

HEAT DISSIPATION PRINCIPLE OF BATTERY HEAT MANAGEMENT SYSTEM

The cool technology hot solution ensures that your car's battery performance is more stable, allowing your battery pack to last longer and let your battery pack perform at its best.

Heat dissipation principle: When the battery works, a lot of heat is generated. The heat transfer silica sheet transfers heat to the water-cooled tube, and the water-cooled tube passes to the coolant. The liquid in the water-cooled tube flows in the battery pack and travels tropically.

The principle of heat dissipation in the battery thermal management system of a well-known automobile manufacturer in China

The principle of heat dissipation: the fan is used to actively dissipate heat, and the fan supplies air. The wind blows away from the battery channel, and the battery pack is tropical.

Heat dissipation principle: Because the internal temperature difference of the battery pack is not controlled within 5 °C, a thermal silica gel sheet is attached to the upper and lower sides of the battery pack, and the silicon wafer is then directed to the outer aluminum shell, and the temperature difference of the entire battery module is controlled within 5 °C. The battery pack design requirements are met, the battery pack has a longer life, and the performance is more stable during driving.

Heat dissipation principle: The battery pack adopts passive heat dissipation, and a thermal conductive silicone sheet is attached between the battery pack and the aluminum heat sink. The silicon wafer transfers the temperature to the aluminum plate, and the aluminum plate exchanges heat with the air.

The principle of heat dissipation: the battery pack adopts passive heat dissipation, and a thermal silica film is attached between the battery pack and the aluminum heat sink. The silicon wafer transfers the temperature to the aluminum heat sink, and the aluminum heat sink exchanges heat with the air.