# A Review on the Thermal Hazards of the Lithium-Ion Battery and the Corresponding Countermeasures
## 5 Management and Countermeasures
### Battery Management System
There are two types of air flow patterns in ACS: natural convection (NC) and forced convection (FC). For the ACS, air flow rate is an important factor in the promotion of the heat transfer coefficient, thus improving the efficiency of heat dissipation. Additionally, certain factors such as battery arrangement, flow path number and width also influence the performance. [PERSON] et al. [241] investigated the thermal behaviors of an air-cooled LIB. Their results showed that temperature non-uniformity caused by heat accumulation and concentration was mitigated by reciprocating air-flow with optimized reversing strategy and forward air-flow. [PERSON] et al. [242] conducted a set of optimization methods in reciprocating air flow of LIB thermal management. They found that the reciprocating flow could achieve good dissipation, reduce the temperature difference, improve the temperature uniformity and effectively reduce the maximum temperature of battery. As displayed in Figure 19, [PERSON] et al. [243] proposed a novel battery pack with a wedge-shaped runner, optimizing the position of inlet/outlet, the width of the wedge-shaped flow path, the inclination angle of the battery and the clearance among batteries. Their results showed that the temperature distribution was exacerbated with the increase of the inlet temperature and improved with the increasing inlet velocity. However, despite the fact that researchers have never stopped optimizing the structure of ACS, it is still hard for ACS to meet the demands of EV at present. [PERSON] et al. [244] argued that using an air-based system it was difficult to cool the battery to less than 52 \({}^{\circ}\)C when the battery temperature was above 66 \({}^{\circ}\)C.  
Compared to the ACS, a liquid-based cooling system possesses better performance due to its higher heat transfer coefficient. Normally, the LCS can be divided into two kinds according to whether a phase change occurs during the process, namely whether water changes into vapor which usually takes place in the heat pipe. Apparently, the phase change may be a driving force in heat absorption. [PERSON] et al. [245] designed a LCS for LIB by varying the contact surface, and the results showed that increasing inlet mass flow could effectively limit the maximum temperature, however, it could not significantly improve the temperature uniformity. As shown in Figure 20, [PERSON] et al. [246] developed two cooling approaches via channeled liquid flow to minimize the thermal non-uniformity in a battery pack and found that the two LCSs could reduce the non-uniformity of battery under 5C discharging operation to values lower than 2.2 and 0.7 \({}^{\circ}\)C, respectively. In addition, [PERSON] et al. [247] developed a new LCS based on thermal silica plates, which could greatly improve the cooling capacity and therefore decrease the maximum temperature difference within a battery. Nevertheless, the fluidity of liquid is a huge barrier for electronic system which requires advanced and complicated design before application, therefore resulting in a high cost. Recently, [PERSON] et al. [248] presented a novel method of employing water evaporation, as displayed in Figure 21. The thin sodium  
Figure 19: A representative air-cooling system. Adopted from Ref. [243]. film (SA-1 film) with a water content of 99 wt.% was prepared and their results revealed that under the condition of a cycle rate larger than 1C, the temperature rise rate of battery could be reduced by half. Meanwhile, the liquid barrier was successfully solved by the proposed SA-1 film such that there was not a large effect on the electronic system. Figure 21: (**a**) The preparation process of thin sodium film (SA-1 film); (**b**) The application of SA-1 film in the system. Adopted from Ref. [248]. Figure 20: The procedure of a representative liquid cooling method. Adopted from Ref. [246]. PCM is a type of material that is able to absorb thermal energy and then release it by a reverse process; hence, it is considered as a novel medium in BMS [249].