Simulation analysis method for thermal propagation of large-capacity battery module based on lumped thermal resistance model

Abstract

The application discloses a large-capacity battery module thermal spread simulation analysis method based on a lumped thermal resistance model, establishes a battery module simulation model composed of a heating unit and multiple batteries stacked in turn, divides the batteries into multiple blocks along the thickness direction, takes each block as a lumped thermal resistance model, makes each lumped thermal resistance model meet a Biot number Bi<0.1, and constructs a battery thermal resistance network model composed of a thermal resistance network of the lumped thermal resistance model; the batteries are heated by the heating unit until thermal runaway occurs, the battery thermal resistance network model is analyzed, and the center temperature curve of each battery is obtained. The method of dividing the batteries into blocks makes the corresponding lumped thermal resistance model of each block meet the requirement of the Biot number, guarantees the accuracy of the thermal spread simulation analysis, is simple in comparison with a finite element simulation analysis method, small in calculation amount, and can realize rapid analysis of the thermal spread simulation of the large-capacity lithium ion battery module.

Description

Technical Field

[0001] This invention belongs to the field of simulation analysis technology, specifically relating to a simulation analysis method for thermal spread of large-capacity battery modules based on a lumped thermal resistance model. Background Technology

[0002] Lithium-ion batteries, characterized by high energy density and long cycle life, have been widely used in electric vehicles, energy storage systems, and other fields. However, with the continuous improvement of battery energy density, the safety issues of power batteries are becoming increasingly prominent, especially the frequent occurrence of thermal runaway accidents, which seriously restricts the large-scale development of electric vehicles. Therefore, in-depth research on battery thermal propagation models is of great significance for ensuring the safe operation of electric vehicles and promoting their large-scale application.

[0003] Currently, finite element method (FEM) software is commonly used for simulation analysis of thermal propagation models in lithium-ion batteries. However, this method suffers from cumbersome preprocessing and long computation time, hindering the rapid evaluation of thermal propagation-related characteristics. While lumped parameter methods simplify the analysis, they also exhibit significant errors when analyzing large-capacity, large-size batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a simulation analysis method for thermal spread of large-capacity battery modules based on a lumped thermal resistance model, so as to solve the problems of long finite element simulation analysis time and large error in the analysis results of lumped parameter methods.

[0005] This invention is achieved through the following technical solution: A simulation analysis method for thermal spread of large-capacity battery modules based on lumped thermal resistance model is proposed. A simulation model of a battery module consisting of heating unit and multiple batteries stacked sequentially is established. The battery is divided into multiple blocks along the thickness direction, and each block is used as a lumped thermal resistance model. Each lumped thermal resistance model satisfies the Biwo number Bi < 0.1. A battery thermal resistance network model composed of thermal resistance networks of lumped thermal resistance models is constructed. The battery is heated by a heating unit until thermal runaway occurs. The battery thermal resistance network model is then analyzed to obtain the center temperature curve of each battery.

[0006] In some embodiments, the battery is divided into k segments along the battery thickness direction. δ is the battery thickness, h is the convective heat transfer coefficient, and λ is the thermal conductivity.

[0007] In some embodiments, in each lumped thermal resistance model, the x-axis is defined as the battery thickness direction, the y-axis as the battery width direction, and the z-axis as the battery height direction. The thermal resistance network of the lumped thermal resistance model is constructed, including: Rx represents the thermal resistance in the x-direction, Ry represents the thermal resistance in the y-direction, Rz represents the thermal resistance in the z-direction, Rh is the convective thermal resistance, Tc is the temperature at the center of the block, Tc_f is the temperature at the front of the block, Tc_b is the temperature at the rear of the block, and T_amb is the ambient temperature. The formula for calculating the thermal resistance of the lumped thermal resistance model is: Rx = Δx / 2 / cond_x / Ax; where Δx is the length of the block in the x-direction, cond_x is the thermal conductivity of the block in the x-direction, and Ax is the area of ​​the block in the x-direction; Ry = Δy / 2 / cond_y / Ay; where Δy is the length of the block in the y direction, cond_y is the thermal conductivity of the block in the y direction, and Ay is the area of ​​the block in the y direction. Rz = Δz / 2 / cond_z / Az; where Δz is the length of the block in the z-direction, cond_z is the thermal conductivity of the block in the z-direction, and Az is the area of ​​the block in the z-direction; The convective thermal resistance of the block in the y direction is Rhy=1 / h / Ay, and the convective thermal resistance in the z direction is Rhy=1 / h / Ay, where h is the convective heat transfer coefficient. The heat capacity of the segment is C = Cp × m, where m is the mass of the segment and Cp is the specific heat capacity of the battery.

[0008] In some embodiments, the battery thermal resistance network model has node terminals at both ends, and the node terminals correspond to the boundary condition of zero heat flow. The thermal resistance network of the heating unit and the thermal resistance network of each block are connected in sequence to form the battery thermal resistance network model.

[0009] In some embodiments, the battery thermal resistance network model is analyzed, wherein: The heat flux of the battery is Q_bat = Cp × m_bat × (dT / dt), where dT / dt is the battery temperature rise rate and m_bat is the battery mass. The heat flow of each block is Q_bat / k, and Q_bati_1=Q_bati_2=……=Q_bati_k-1=Q_bati_k=Q_bat / k, where Q_bati_k represents the heat flow of the kth block of the i-th battery; When k is odd, Tc_bati_(k+1) / 2 is obtained as the center temperature of the i-th battery, where Tc_bati_(k+1) / 2 represents the center temperature of the (k+1) / 2th block of the i-th battery; When k is even, Tc_bati_k / 2_b is obtained as the center temperature of the i-th battery, where Tc_bati_k / 2_b represents the rear temperature of the k / 2-th block of the i-th battery.

[0010] In some embodiments, the center temperature curve of the battery is obtained based on the relationship between the center temperature of the battery and time. The thermal runaway time and the maximum temperature of each battery are obtained based on the center temperature curve of each battery. The thermal runaway time is the time corresponding to when the battery temperature rise rate reaches a preset value.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention employs a method of dividing the battery into blocks, ensuring that the lumped thermal resistance model corresponding to each block meets the requirements for the Biot number. Based on the lumped thermal resistance model, a battery thermal resistance network model is established. In the battery thermal resistance network model, the battery heat flow is evenly distributed, and the thermal runaway of the battery is triggered in blocks, ensuring the accuracy of thermal propagation simulation analysis. Compared with the finite element simulation analysis method, the analysis process is simpler and the amount of calculation is smaller, enabling rapid analysis of thermal propagation simulation of large-capacity lithium-ion battery modules. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the battery module simulation model structure in an embodiment of the present invention.

[0014] Figure 2 This is the simulation analysis process for the lumped thermal resistance model in this embodiment of the invention.

[0015] Figure 3 This is a schematic diagram of the battery being divided into blocks in an embodiment of the present invention.

[0016] Figure 4 This is a schematic diagram of the thermal resistance network structure of the lumped thermal resistance model in an embodiment of the present invention.

[0017] Figure 5 This is a schematic diagram of the battery thermal resistance network model structure in an embodiment of the present invention.

[0018] Figure 6 This is a graph showing the battery temperature rise rate in an embodiment of the present invention.

[0019] Figure 7 This is a schematic diagram comparing the battery center temperature curves of the two analysis methods in this embodiment of the invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, specific embodiments of this application will be described in further detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely for explaining this application and not for limiting it. It should also be noted that, for ease of description, only the parts relevant to this application are shown in the drawings, not all of them. Before discussing exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe operations (or steps) as sequential processes, many of these operations can be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but may also have additional steps not included in the drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0021] The finite element simulation analysis method divides the battery into a large number of mesh elements, which are connected by node sharing and mathematical functions. The temperature transition within each small mesh element is smooth, which can describe the continuous temperature change of the battery. It has high calculation accuracy, but the amount of computation is very large.

[0022] The lumped parameter analysis method connects the lumped blocks together through thermal resistance, allowing heat to be transferred from one lumped block to another. Each lumped block has only one temperature value, and the interior of the lumped block is completely uniform with the same temperature everywhere. The calculation accuracy is not as high as that of the finite element simulation analysis method, but the calculation speed is faster.

[0023] like Figure 1 This is a simulation model of a battery module consisting of a heating unit and two batteries stacked together in this embodiment. The battery module simulation model consists of a heating unit, battery 1 and battery 2 arranged in sequence. The heating unit is located on one side of battery 1 and battery 2 is located on the other side of battery 1.

[0024] This embodiment uses a battery module simulation model including two batteries as an example to illustrate the thermal propagation simulation analysis method of the present invention.

[0025] Reference Figure 2 The lumped parameter method for analyzing the lumped thermal resistance model requires the Biot number Bi < 0.1, where Bi = δh / λ, δ is the battery thickness, h is the battery convective heat transfer coefficient, and λ is the battery thermal conductivity. However, as the battery capacity increases, the battery size also increases. When directly using the lumped parameter method for analysis, the Biot number Bi will be greater than 0.1. Therefore, for large-capacity lithium-ion batteries, if the battery is directly used as the lumped thermal resistance model for thermal resistance analysis, the analysis results will have a large error.

[0026] like Figure 3In this embodiment, the battery is divided into k segments along the thickness direction, and Each segment of the battery is treated as a separate lumped thermal resistance model; in this case, each lumped thermal resistance model can satisfy the condition that Bi < 0.1, thus ensuring the analytical accuracy of the lumped parameter analysis method.

[0027] like Figure 4 This is a schematic diagram of the thermal resistance network structure for each lumped thermal resistance model. For the lumped thermal resistance model, let the x-axis represent the battery thickness, the y-axis represent the battery width, and the z-axis represent the battery height. The thermal resistance network of the lumped thermal resistance model is constructed as follows: Rx represents the thermal resistance in the x-direction, Ry represents the thermal resistance in the y-direction, Rz represents the thermal resistance in the z-direction, Rh is the convective thermal resistance, Tc is the temperature at the center of the block, Tc_f is the temperature at the front of the block, Tc_b is the temperature at the rear of the block, and T_amb is the ambient temperature. The formula for calculating the thermal resistance of the lumped thermal resistance model is: Rx = Δx / 2 / cond_x / Ax; where Δx is the length of the block in the x-direction, cond_x is the thermal conductivity of the block in the x-direction, and Ax is the area of ​​the block in the x-direction; Ry = Δy / 2 / cond_y / Ay; where Δy is the length of the block in the y direction, cond_y is the thermal conductivity of the block in the y direction, and Ay is the area of ​​the block in the y direction. Rz = Δz / 2 / cond_z / Az; where Δz is the length of the block in the z-direction, cond_z is the thermal conductivity of the block in the z-direction, and Az is the area of ​​the block in the z-direction.

[0028] The convective thermal resistance in the y-direction is Rhy=1 / h / Ay, and the convective thermal resistance in the z-direction is Rhy=1 / h / Ay, where h is the convective heat transfer coefficient.

[0029] Heat capacity C = Cp × m, where m is the mass of the block and Cp is the specific heat capacity of the battery.

[0030] by Figure 1 Taking the battery module simulation model as an example, a battery thermal resistance network model is constructed based on the thermal resistance network of each block. The two ends of the battery thermal resistance network model are node terminals, and the node terminals correspond to the boundary condition of zero heat flow. The left side of the battery thermal resistance network model is the thermal resistance network of the heating unit. The thermal resistance network of the heating unit is connected to the thermal resistance network of the first block of battery 1. The thermal resistance networks of each block of battery 1 are connected in sequence. The thermal resistance network of the kth block of battery 1 is connected to the thermal resistance network of the first block of battery 2. The thermal resistance networks of each block of battery 2 are connected in sequence to form the battery thermal resistance network model.

[0031] The heating unit serves as the heat source that triggers battery thermal runaway, and its heating power can be set to Q_heat=600W. The battery heat flow is obtained through adiabatic thermal runaway experiments, i.e., Q_bat=Cp×m_bat×(dT / dt), where dT / dt is the temperature rise rate and m_bat is the battery mass.

[0032] In the battery thermal resistance network model, the heat flow corresponding to each block is Q_bat / k, where Q_bat1_1=Q_bat1_2=……=Q_bat1_k-1=Q_bat1_k=Q_bat / k. Q_bat2_1=Q_bat2_2=……=Q_bat2_k-1=Q_bat2_k=Q_bat / k.

[0033] Analysis software such as Simulink and SimCape were used to analyze the battery thermal resistance network model. When the battery reached the thermal runaway trigger temperature, the heating unit stopped heating and the center temperature curve of each battery was obtained.

[0034] When k is odd, obtain Tc_bat1_(k+1) / 2 and Tc_bat2_(k+1) / 2 as the center temperatures of battery 1 and battery 2, that is, Tc_bat1=Tc_bat1_(k+1) / 2, Tc_bat2=Tc_bat2_(k+1) / 2; When k is even, obtain Tc_bat1_k / 2_b and Tc_bat2_k / 2_b as the center temperatures of battery 1 and battery 2, that is, Tc_bat1=Tc_bat1_k / 2_b and Tc_bat2=Tc_bat2_k / 2_b.

[0035] This invention employs a block-based approach, ensuring the solution accuracy of each block and enabling the solution accuracy of the entire battery module to meet the requirements of analytical precision.

[0036] The following analysis, using specific examples, compares the accuracy of the analysis results obtained by the method of this invention and the finite element simulation analysis method, highlighting the difference in the battery center temperature obtained by the two methods. Neither method considers additional contact thermal resistance or other additional thermal resistance.

[0037] In one embodiment, the battery is divided into sections, each with the following dimensions: thickness Δx = 33.5 mm, width Δy = 220 mm, and height Δz = 102 mm. Area in the x direction Area in the y direction area in the z-direction ; Thermal conductivity: cond_x = 1.1 W / (m•K), cond_y = 15.3 W / (m•K), cond_z = 15.3 W / (m•K); Convective heat transfer coefficient h = 20 W / (m 2 •K); Conductive thermal resistance: Rx=Δx / 2 / cond_x / Ax, Ry=Δy / 2 / cond_y / Ay, Rz=Δz / 2 / cond_z / Az; Convection thermal resistance: Rhy = 1 / h / Ay, Rhy = 1 / h / Ay; Number of blocks: , where δ=Δx, λ=cond_x; Heating unit Q_heat = 600W; Battery heat flux: Q_bat = Cp × m_bat × (dT / dt), where dT / dt is the temperature rise rate, obtained through battery ARC experiments, such as... Figure 6 As shown.

[0038] Thermal runaway time is defined as the time corresponding to when the battery temperature rise rate reaches 1℃ / s.

[0039] Using the above data, the battery thermal resistance network model is solved in the analysis software to obtain the battery's center temperature. Based on the relationship between the battery center temperature and time, the battery center temperature curve is obtained, as shown below. Figure 7 As shown in the figure, the black solid line is the center temperature curve obtained from the lumped analysis of battery 1, the black dashed line is the center temperature curve obtained from the finite element simulation analysis of battery 1, the blue solid line is the center temperature curve obtained from the lumped analysis of battery 2, and the blue dashed line is the center temperature curve obtained from the finite element simulation analysis of battery 2.

[0040] from Figure 7 As can be seen from the data, the highest temperature of battery 1 obtained by the finite element simulation analysis method is 774℃, and the thermal runaway time is 318s. The highest temperature of battery 2 is 843℃, and the thermal runaway time is 540s.

[0041] The highest temperature of battery 1 obtained by the simulation analysis method of this invention is 804℃ and the thermal runaway time is 343s. The highest temperature of battery 2 is 840℃ and the thermal runaway time is 576s.

[0042] The comparison shows that the results of the method of the present invention are close to those of the finite element simulation analysis. The differences in the highest temperature of battery 1 and battery 2 obtained by the two analysis methods are 3.88% and 0.36%, respectively, and the differences in thermal runaway time are 7.86% and 6.67%, respectively. This indicates that the method of the present invention can achieve the same accuracy as the finite element simulation analysis.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A simulation analysis method for thermal spread of large-capacity battery modules based on a lumped thermal resistance model, characterized in that, A battery module simulation model consisting of heating units and multiple batteries stacked sequentially is established. The battery is divided into multiple blocks along the thickness direction, and each block is used as a lumped thermal resistance model. Each lumped thermal resistance model satisfies the Biwo number Bi < 0.

1. A battery thermal resistance network model composed of the thermal resistance network of the lumped thermal resistance models is constructed. The battery is heated by a heating unit until thermal runaway occurs. The battery thermal resistance network model is then analyzed to obtain the center temperature curve of each battery.

2. The simulation analysis method for thermal spread of large-capacity battery modules based on the lumped thermal resistance model according to claim 1, characterized in that, The battery is divided into k segments along its thickness direction. δ is the battery thickness, h is the convective heat transfer coefficient, and λ is the thermal conductivity.

3. The simulation analysis method for thermal spread of large-capacity battery modules based on the lumped thermal resistance model according to claim 1, characterized in that, In each lumped thermal resistance model, let the x-axis represent the battery thickness, the y-axis represent the battery width, and the z-axis represent the battery height. Construct the thermal resistance network for the lumped thermal resistance model, including: Rx represents the thermal resistance in the x-direction, Ry represents the thermal resistance in the y-direction, Rz represents the thermal resistance in the z-direction, Rh is the convective thermal resistance, Tc is the temperature at the center of the block, Tc_f is the temperature at the front of the block, Tc_b is the temperature at the rear of the block, and T_amb is the ambient temperature. The formula for calculating the thermal resistance of the lumped thermal resistance model is: Rx = Δx / 2 / cond_x / Ax; where Δx is the length of the block in the x-direction, cond_x is the thermal conductivity of the block in the x-direction, and Ax is the area of ​​the block in the x-direction; Ry = Δy / 2 / cond_y / Ay; where Δy is the length of the block in the y direction, cond_y is the thermal conductivity of the block in the y direction, and Ay is the area of ​​the block in the y direction. Rz = Δz / 2 / cond_z / Az; where Δz is the length of the block in the z-direction, cond_z is the thermal conductivity of the block in the z-direction, and Az is the area of ​​the block in the z-direction; The convective thermal resistance of the block in the y direction is Rhy=1 / h / Ay, and the convective thermal resistance in the z direction is Rhz=1 / h / Az, where h is the convective heat transfer coefficient. The heat capacity of the segment is C = Cp × m, where m is the mass of the segment and Cp is the specific heat capacity of the battery.

4. The simulation analysis method for thermal spread of large-capacity battery modules based on the lumped thermal resistance model according to claim 3, characterized in that, The battery thermal resistance network model has node terminals at both ends, and the node terminals correspond to the boundary condition of zero heat flow. The thermal resistance network of the heating unit and the thermal resistance network of each block are connected in sequence to form the battery thermal resistance network model.

5. The simulation analysis method for thermal spread of large-capacity battery modules based on the lumped thermal resistance model according to claim 4, characterized in that, An analysis of the battery thermal resistance network model is performed, in which: The heat flux of the battery is Q_bat = Cp × m_bat × (dT / dt), where dT / dt is the battery temperature rise rate and m_bat is the battery mass. The heat flow of each block is Q_bat / k, and Q_bati_1=Q_bati_2=……=Q_bati_k-1=Q_bati_k=Q_bat / k, where Q_bati_k represents the heat flow of the kth block of the i-th battery; When k is odd, Tc_bati_(k+1) / 2 is obtained as the center temperature of the i-th battery, where Tc_bati_(k+1) / 2 represents the center temperature of the (k+1) / 2th block of the i-th battery; When k is even, Tc_bati_k / 2_b is obtained as the center temperature of the i-th battery, where Tc_bati_k / 2_b represents the rear temperature of the k / 2-th block of the i-th battery.

6. The simulation analysis method for thermal spread of large-capacity battery modules based on the lumped thermal resistance model according to claim 5, characterized in that, The battery center temperature curve is obtained based on the relationship between the battery center temperature and time. The thermal runaway time and maximum temperature of each battery are obtained based on the center temperature curve of each battery. The thermal runaway time is the time corresponding to when the battery temperature rise rate reaches a preset value.

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