## 1 Introduction  
The ways to deal with the energy crisis and environmental pollution and develop new energy of safety and cleanness have become the focus of the attention of all countries in the world. It also becomes the core issue to solve the sustainable development of humankind. LIBs, which have the advantages of high specific energy, relatively high operating voltage, long cycle life, low self-discharge rate, small and convenient, are considered to be one of the most promising energy storage devices [1; 2; 3]. However, if the operating temperature of LIB is high and the heat dissipation is not timely, it will lead to thermal failure, shorten the service life of LIB and cause safety problems, such as fire and explosion [4; 5]. Therefore, the thermal safety of LIB needs to be focused on. The temperature difference between battery internal and ambient, as well as the temperature difference between the cells inside the battery pack will have a negative impact on the performance, life and safety of the battery [6]. Therefore, it is necessary to conduct a reasonable heat management system to make the LIB working in the normal operating temperature range [7; 8; 9; 10]. At present, there are three kinds of mainstream thermal management methods for LIBs including air cooling, liquid cooling and PCM cooling [11]. Air cooling is divided into natural air cooling and forced air cooling. [PERSON] et al. studied the air cooling performance of the battery thermal management system (BTMS). The results showed that the air cooling could effectively reduce the battery temperature and keep the battery temperature consistent in a low rate discharging [12]. [PERSON] et al. studied the thermal management system using air cooling of metal foam-based heat exchanger plate. The system showed that the LIB temperature decreased with the increase of airflow. However, the thermal conductivity of air is low and the heat dissipation is weak [13]. Compared with the air cooling method, the liquid cooling method has higher thermal conductivity, which leads to higher cooling performance and is more suitable for cooling large battery packs. Liquid cooling is divided into direct and indirect liquid cooling. [PERSON] et al. compared different liquid cooling systems of LIB, and the results showed that the indirect liquid cooling system had the lowest temperature rise and was more practical than direct liquid cooling [14]. [PERSON] et al. applied the S-type guide plate to the integrated module of liquid cooling heat dissipation system, and found that the device could avoid heat concentration, improve heat transfer performance and keep the temperature of LIB uniform [15]. However, the traditional battery thermal management method that uses cheap air and water as the cooling medium requires additional energy to drive the cooling medium circulation. In battery thermal management applications, the battery's safe operating temperature is often sacrificed at the expense of battery capacity and power in exchange for longer operating life, and these traditional thermal management methods are complex and occupy a large space [16]. In recent years, researchers have found that PCMs exhibit excellent performance in thermal management of LIB [17; 18] since they have large storage density apart of many other advantages [19; 20; 21]. [PERSON] et al. conducted the numerical and experimental studies on PCM heat transfer, and found that they have great potential in thermal management due to potential energy storage and controllable temperature stability [22]. PCM battery management system which performed better than traditional thermal management system was first proposed and patented by [PERSON] and [PERSON] [23; 24]. [PERSON] and [PERSON] used the entropy coefficient method to simulate the battery pack, and the results showed that using a PCM could significantly improve the system performance and keep the operating temperature below 55 \({}^{\circ}\)C, even at high discharge rate [25]. [PERSON] et al.