The key points of the design of the thermal management system for lithium battery packs mainly cover system functional goals, selection of heat dissipation methods, design of key components, formulation of control strategies, as well as system testing and optimization. The following is a detailed elaboration for you:

System functional objective

Temperature control: The operating temperature of lithium battery packs should be kept within an appropriate range. Generally, the suitable operating temperature range for batteries is 20°C to 40°C. For example, in a high-temperature environment, when the battery temperature approaches 40°C, the thermal management system needs to activate heat dissipation measures to prevent the battery temperature from being too high. In a low-temperature environment, when the battery temperature approaches 0°C, heating measures should be taken to ensure that the battery can charge and discharge normally.

Temperature uniformity: Ensure that the temperature differences among individual battery cells within the battery pack are as small as possible, generally not exceeding 5°C. If the temperature difference within the battery pack is too large, it will lead to a decline in the performance of some batteries, affecting the lifespan and safety of the entire battery pack. For instance, in a battery pack composed of multiple individual cells, if the temperature of some cells is too high, it may accelerate their aging, while those cells with too low a temperature may not be able to fully exert their performance.

Selection of heat dissipation method

Air-cooling system: It uses fans to force air flow and remove the heat generated by the battery. Its advantages are simple structure, low cost and convenient maintenance. For instance, in some small electric equipment that is sensitive to cost, air-cooling systems are often adopted. However, the heat dissipation efficiency of air-cooled systems is relatively low and is greatly affected by ambient temperature and air flow. In high-temperature environments, they may not be able to meet the heat dissipation requirements.

Liquid cooling system: Heat is carried away by the circulation of coolant in the pipes inside the battery pack. The liquid cooling system has a high heat dissipation efficiency, can quickly and effectively reduce the battery temperature, and has good temperature uniformity. However, the structure of the liquid cooling system is relatively complex, with a high cost. It requires an additional coolant circulation system and sealing devices, and there is also a risk of coolant leakage.

Phase change material cooling: It utilizes the property of phase change materials to absorb or release a large amount of heat during phase change to control the battery temperature. The phase change material cooling system has the advantages of stable temperature control and no need for additional power equipment. For instance, some phase change materials can absorb a large amount of heat during the melting process, thereby maintaining the stability of the battery temperature. However, the thermal conductivity of phase change materials is generally poor, and they need to be used in combination with other thermal conductive materials. Moreover, the cost of phase change materials is relatively high, and there are also certain difficulties in their recycling and reuse.

Design of Key Components

Heat dissipation components: For air-cooling systems, the main heat dissipation components are heat sinks and fans. The design of heat sinks should take into account their shape, size and material to increase the heat dissipation area and improve the heat dissipation efficiency. For example, the use of finned heat sinks can increase the contact area with the air. The selection of fans should be determined based on the heat dissipation requirements of the battery pack and the size of the space, ensuring sufficient air volume and air pressure. For liquid cooling systems, heat dissipation components include radiators, cooling pipes, etc. The radiator should have highly efficient heat dissipation performance. The design of the cooling pipes should be reasonable to ensure that the coolant can flow evenly through each battery cell.

Heating components: In low-temperature environments, heating components need to be used to heat the battery pack. Common heating components include heating films, heating wires, etc. The heating film has the advantages of uniform heating and thin thickness, and is suitable for application on the surface of batteries. The heating wire can be bent and arranged as needed, but the uniformity of heating is relatively poor. The power of the heating component should be determined based on the capacity of the battery pack and the heating requirements in low-temperature environments.

Heat-conducting component: The function of the heat-conducting component is to quickly conduct the heat generated by the battery to the heat dissipation component. Commonly used heat-conducting components include heat-conducting silicone pads, heat-conducting adhesives, etc. Thermal conductive silicone pads have excellent flexibility and thermal conductivity, which can fill the gap between the battery and the heat dissipation components and improve the thermal conductivity efficiency. Thermal conductive adhesive can firmly bond the battery to the heat dissipation components, reducing thermal resistance.

Formulation of control strategies

Temperature monitoring: Temperature sensors are reasonably arranged within the battery pack to monitor the temperature changes of the batteries in real time. The accuracy and response speed of the temperature sensor must meet the requirements to ensure that the temperature information of the battery can be accurately obtained. For example, high-precision thermocouples or thermistors are adopted as temperature sensors.

Control logic: Based on the temperature monitoring results, formulate the corresponding control logic. When the battery temperature exceeds the set upper limit value, the heat dissipation measures are activated. When the battery temperature is lower than the set lower limit value, the heating measure is activated. At the same time, the power for heat dissipation or heating should be reasonably adjusted according to the changes in battery temperature. For instance, when the battery temperature approaches the upper limit, start the heat dissipation device at a lower power first. If the temperature continues to rise, gradually increase the heat dissipation power.

Fault diagnosis and protection: The thermal management system should be equipped with fault diagnosis and protection functions, capable of promptly detecting faults in the system, such as temperature sensor failure, fan failure, coolant leakage, etc., and taking corresponding protective measures, such as stopping the charging and discharging of the battery pack and issuing an alarm, to ensure the safety of the battery pack.

System testing and optimization

Performance testing: After the thermal management system design is completed, performance testing should be conducted on it, including heat dissipation efficiency testing, temperature uniformity testing, heating efficiency testing, etc. Through performance testing, evaluate whether the thermal management system meets the design requirements. For instance, under different ambient temperatures and charge and discharge rates, test the temperature changes of the battery pack to check whether the heat dissipation and heating effects meet expectations.

Optimization and improvement: Based on the results of performance tests, optimize and improve the thermal management system. If insufficient heat dissipation efficiency is found, the structure of the heat dissipation components can be adjusted or the heat dissipation area can be increased. If the temperature uniformity is not good, the layout of the cooling pipes can be optimized or the design of the heat-conducting components can be improved. Through continuous testing and optimization, the performance and reliability of the thermal management system are improved.