About the decomposition of lithium battery heat dissipation characteristics

The heat of the lithium battery can be divided into two categories according to the source: 1) reversible entropy heat; 2) irreversible heat, such as ohmic resistance heat, charge exchange resistance heat, etc., so the heat generation power of the lithium battery in the working process It can be expressed by the following formula, where the first term is irreversible heat and the second term is reversible entropy heat. In addition to heat generation, heat dissipation of lithium batteries is also important. The heat dissipation characteristics of lithium batteries are affected by the shape of the battery, battery materials and heat dissipation methods. In this study, the author proposed a standard heat dissipation coefficient concept. In the experiment, the author will dissipate heat. The method is unified into a more efficient pole heat dissipation method, thus guarding against the influence of the battery shape on the heat dissipation coefficient. In the experiment, the author used two sizes of soft pack lithium batteries as the research object, and the battery parameters are shown in the following table. Among them, battery A is a high-power 5Ah battery, battery B is a high-density 7.5Ah battery, the positive electrode of battery A is made of NCM111 material, and the positive electrode of battery B is made of Li(Ni0.4Co0.6)O2 material. Table 2 shows two types. The basic parameters and thermal characteristics of the internal cells of the battery. The device used to detect the heating characteristics of batteries A and B in the experiment is shown in the figure below. The bus bar used for electrical connection also serves the purpose of heat dissipation of the tabs. In the experiment, the author used 15 K-type thermocouples. For measuring battery and oven temperature changes, the detailed distribution of these thermocouples is shown in the figure below. The heat dissipation rate of the battery through the positive and negative bus bars can be expressed by the following formula, where the cross-sectional area of u200bu200bthe ABB bit bus bar and the temperature difference between the two temperature measurement points on the ΔTBBneg bit bus bar are related to the temperature measurement of the negative poles No. 9 and No. 10 The temperature difference between the points, for the positive electrode, the temperature difference between the 11 and 12 temperature measurement points. In order to measure the heating characteristics of the lithium battery in different SoC states, the author adopts a pulse discharge strategy, which is 20A Pulse charging for 1s, then 20A pulse discharge for 1s, continue for 6 hours to ensure that the battery maintains the same SoC throughout the process. The heat in this process comes from irreversible heat. When using tabs to dissipate heat, the temperature difference inside the battery is less than 1℃, and if a heating condition of 1.49W is applied to one side of the battery, the maximum temperature difference inside the battery will increase to 3℃ (as shown in figure c below). Applying a 1.49W heating on both sides of the battery at the same time, we can see from the figure d below that the temperature difference inside the battery has become very small. From the simulation results, pulse charging and discharging can appear in the lithium battery. Average temperature field. The thermal power curve can be divided into two categories: 1) heat production power; 2) heat dissipation power. From the figure below, it can be seen that the temperature of the battery will slowly increase during the initial unsteady state. The temperature difference in the heat dissipation area of u200bu200bthe bus bar is increasing, and the heat dissipation power of the battery through the bus bar is also increasing. When the heat generation power and the heat dissipation power are equal, the battery reaches a steady state. Since the heat of the lithium battery in this experiment is mainly diffused through the positive electrode tab and the negative electrode tab, when calculating the heat dissipation coefficient of the lithium battery, the author also calculated the negative heat dissipation coefficient CCCneg, the positive heat dissipation coefficient CCCpos, and the total heat dissipation of the battery. The coefficient CCCtot (shown in the following formula). The figure below shows the three heat dissipation coefficients calculated using the steady-state data in Experiment 1. From the figure below, we can see that the heat dissipation coefficient of the negative electrode is significantly higher than that of the positive electrode. The heat dissipation coefficients of the positive electrode, negative electrode and battery of battery A1 calculated under different SoCs and different currents. From the figure below, it is not difficult to see that the battery's SoC state and operating current have no effect on the heat dissipation coefficient of the battery. This statement no matter where the battery is In this working condition, as long as the thermal balance can be achieved, we can calculate the heat dissipation coefficient of the battery. Comparing the heat dissipation coefficients of the two batteries A and B, it can be seen that the heat dissipation coefficient of the negative electrode of the two batteries is significantly higher than that of the positive electrode, and the heat dissipation coefficient of battery A is clearly higher than that of the battery A because of the power-type design. For battery B, the negative electrode heat dissipation coefficient of battery A is 65.13% higher than that of battery B, the positive heat dissipation coefficient is 63.18% higher, and the overall heat dissipation coefficient of the battery is 62.70% higher. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: What are the characteristics of competition in the lithium battery separator industry?