Temperature is very important for lithium- ion batteries. Low temperature will reduce the electrical performance of lithium- ion batteries (capacity, rate performance), but it can improve the storage life of lithium- ion batteries. High temperature can improve electrical performance (capacity, rate performance), but It will reduce the stability of the electrode/electrolyte interface and cause a rapid decline in cycle life. For a battery pack consisting of many cells, the uneven temperature distribution inside the battery pack will cause a large difference in the performance of the single cells, resulting in uneven decay between the single cells, and ultimately lead to the battery pack. For example, QuanXia et al. of Peking University used A123 LFP batteries to simulate and simulate the battery pack and found that by changing the structure of the battery pack, reducing the maximum temperature difference in the battery pack from 4.62K to 2.5K can reduce the battery pack. The reliability after accumulative charging of 600Ah increased from 0.0635 to 0.9328 (see link: "Influencing factors and model calculation of battery pack "reliability"). The operating conditions of lithium- ion batteries have a great impact on the heat generation of ion batteries. For example, high-rate charge and discharge will accumulate more heat in the battery for a short time , while at low rates, thermal balance can be almost achieved, reducing battery temperature. Lift. Recently, the heat generation power and temperature distribution of 55Ah single cells and battery packs have been studied and analyzed. The research shows that the heating power of single cells will decrease with the increase of ambient temperature, the decrease of battery SoC and the charge-discharge rate. Thermal analysis of the battery pack found that the hottest areas were concentrated in the center of the battery pack, and it was found that when air was used for cooling, the airflow was more likely to flow over the top of the battery pack, resulting in poor cooling.

A 55Ah square lithium- ion battery was used in the test. The battery has five temperature measurement points, two of which are located at the lower part of the battery and three are located on the side of the lithium- ion battery, as shown in Figure a below. The heat production of the battery can be calculated by the temperature rise and the specific heat capacity of the battery (as shown in the following formula), where Q is the heat production of the battery, Cp is the specific heat capacity of the battery, m is the mass of the battery, and DT is the temperature rise of the battery. By dividing the following formula by the time t, we can get the heat production power of the battery.

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