A Study on Thermal Management of Lithium Ion Battery Pack

Abstract

In the face of global energy shortage and environment pollution， the development of new energy has become the direction of scientific research in recent years. The Lithiumion battery has attracted much attention for its good safety, specific energy, specific capacity, cycle life and other advantages. Temperature has a significant effect on battery performance during battery operation. If the temperature is too high or too low, or the temperature distribution is uneven, the battery capacity decreases. The use of efficient battery thermal management system is very important to ensure battery performance. During charging and discharging, most of the battery's capacity is used to drive the load, and a small portion of the energy forms parasitic power in the form of heat. This part of the heat if not dissipated in time, will directly threaten the safety of the battery system.-ixTherefore, it is necessary to optimize the thermal management system of battery system to improve its heat dissipation performance. In this paper, it was the target that the maximum temperature and temperature difference were decreased to ensure the optimal working temperature range for lithium ion battery under different cooling system using different methods. The structure optimization of air cooling, liquid cooling, phase change materials and the coupling between liquid cooling and phase change materials was carried out according to the power battery of different application scenarios. In phase change materials, the influence of melting temperature on the cooling performance of phase change materials was simulated. Specific work to be carried out includes the following aspects: It was to decrease the heat generation inside battery as the starting point. As for air cooling， the place between electrode terminal and battery body was optimized by adding the material that conduct electricity better. It was to find the appropriate thickness to decrease the maximum temperature. Meanwhile, the space and tilt angle between batteries were adjusted to achieve the optimal working temperature. When the space was 3.5 mm and the tilt angle was 2.5°， the results was best for air cooling in this case. The liquid cooling is used to high power situation. The reasonable layout of cooling pipe can effectively reduce the number of pipes. Meanwhile, the suitable flow rate of liquid can improve the cooling efficiency of liquid to decrease the extra energy consumption, so the 0.9 m/s was selected. By the way, the circle shape was selected as the section of cooling pipe. The phase change material can help batteries temperature more uniform. So, the thickness and layout of phase change material were studied to make the better plan to-xdecrease the temperature difference. The coupling cooling system of liquid cooling and phase change material was designed according to the reasonable layout of phase change material. The melting temperature of phase change material was researched in coupling cooling system. When the melting temperature was 302.6 K, the temperature distribution of battery pack was more uniform. It can be found that the maximum temperature and temperature difference were reduced at the end of discharge in different cooling system by the optimization results. First, the structure of single battery was optimized to decrease heat generation. The amount of heat generation can be decreased effectively by the suitable thickness of added material and reasonable layout of tab terminal. Then, the structure for battery pack and some parameters were adjusted to enhance cooling performance. The appropriate spacing “d” and pitch “θ” between batteries can improve cooling performance under air cooling method. The reasonable selection of cooling pipe section, flow rate of coolant and position of cooling pipe can decrease maximum temperature to improve cooling performance in liquid cooling method. At the last, the PCM was adopted to improve temperature uniformity in coupling cooling method. The reasonable melting temperature can helpfully boost temperature uniformity. The optimization result was shown as followed: The maximum temperature was 311.6 K in 1P7S battery pack under air-cooling system. When the flow rate of cooling liquid was 0.09 m/s, the maximum temperature was 307.18 K, and the maximum temperature difference between batteries was 8.51 K in 1P7S battery pack under liquid-cooling system. The maximum temperature and maximum temperature difference were 305.54 K and 5.65 K, respectively in coupling cooling system which was based on liquid cooling system