1 Establish a three-dimensional transient heat transfer mathematical model for lithium-ion batteries (1) Due to the poor fluidity of the electrolyte inside the battery, the convective heat transfer inside the battery can be ignored; (2) The internal radiation of the battery has very little effect on heat dissipation , So it can be ignored; (3) The various materials inside the battery are isotropic, so the temperature inside the battery changes only in the radial direction and does not change in other directions; (4) The heat is evenly generated inside the battery . In the above-mentioned four assumptions, since the two ends of the battery also dissipate heat, the third assumption is removed, and a three-dimensional transient heat transfer mathematical model of cylindrical lithium-ion batteries can be established: (1) where: t is the battery’s Temperature, ℃; ρ is the density of the battery, kg/m3; c is the specific heat capacity of the battery, J/ (kg·℃); τ is the time, s; l is the thermal conductivity of the battery, W/(m·℃); r Is the radius of the battery, m; φ is the circumferential angle of the battery, rad; z is the length of the battery, m; Q is the heat generation rate per unit volume inside the battery, W/m3. 2 Establish the three-dimensional finite element model of the lithium ion battery Cylindrical lithium-ion batteries are symmetrical about the middle plane in the axial direction, so half of the axial direction can be used to establish the finite element model of the lithium-ion battery; and because the lithium-ion battery is axisymmetric in the radial direction, it is desirable in the radial direction One quarter builds a finite element model of a lithium-ion battery. The established three-dimensional finite element model of cylindrical lithium-ion battery is shown in Figure 1. 3 Determination of internally generated heat There are two main methods for determining internally generated heat: one is to directly measure through experiments; the other is to calculate by formula, as shown in (2): (2) where Q is the internal unit of the battery Heat generation rate of volume, W/m3; I is the discharge current of the battery, A; V is the total volume of the battery, m3; T is the temperature of the battery, ℃; Eoc is the open circuit voltage of the battery, V; E is the working of the battery Voltage, V; Eoc-E u003d IR (R is the internal resistance of the battery), only changes in a small range, and its value is equal to -0.5 mV/K. From this we can calculate the heat generation rate of the ICR65/400 lithium-ion battery when discharged at 1 C. The results are shown in Table 1. 4 Result analysis The performance parameters of ICR65/400 lithium-ion battery are shown in Table 2. Assume that the temperature of the battery at the beginning of the discharge is 300 K, and the temperature of the surrounding fluid is 300 K. Using these data, two-dimensional analysis and three-dimensional analysis of the temperature field of the ICR65/400 lithium-ion battery were carried out, and the results of the two were analyzed and compared. Finally, the influence of different convective heat transfer coefficients on the battery temperature field was analyzed. First, on the basis of two-dimensional analysis, the temperature field of ICR65/400 lithium battery pack
was analyzed in three dimensions using the finite element analysis software ANSYS. After analysis and comparison, three-dimensional analysis is more accurate than two-dimensional analysis. Next, the influence of different convective heat transfer coefficients on the battery temperature field is analyzed. The results show that as the convective heat transfer coefficient increases, its influence on the maximum temperature of the battery is smaller. Therefore, the larger the convective heat transfer coefficient, the better. 5 Conclusion Based on the two-dimensional analysis, this paper firstly used the finite element analysis software ANSYS to analyze the temperature field of the ICR65/400 lithium battery pack. After analysis and comparison, three-dimensional analysis is more accurate than two-dimensional analysis. Next, the influence of different convective heat transfer coefficients on the battery temperature field is analyzed. The results show that as the convective heat transfer coefficient increases, its influence on the maximum temperature of the battery is smaller. Therefore, the larger the convective heat transfer coefficient, the better. Attached document download: Three-dimensional temperature field analysis of lithium-ion batteryu003c/pu003e
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