Method for determining thickness of thermal insulation layer in liquid-cooled battery module

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a method for determining the thickness of a heat insulation layer in a liquid-cooled battery module. The method for determining the thickness of the thermal insulation layer comprises the following steps: carrying out ARC test on a battery cell to obtain a battery cell thermal runaway characteristic parameter; carrying out thermal diffusion modeling and thermal runaway diffusion simulation on the liquid-cooled battery module, giving material types of thermal insulation layers, and obtaining minimum liquid-cooled system convection coefficients without thermal diffusion under multiple groups of thermal insulation layers with different thicknesses; and fitting the minimum liquid cooling system convection coefficient and the corresponding thermal insulation layer thickness to obtain a curve, and further obtaining the thermal insulation layer thickness without thermal diffusion. Through theoretical analogue simulation, the relationship between the thermal insulation layer thickness and the convection coefficient of the liquid cooling system is disclosed on the premise that thermal runaway diffusion does not occur, the thermal insulation layer thickness without thermal diffusion can be obtained, the development period is shortened, and the development cost is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a method for determining the thickness of a heat insulation layer in a liquid-cooled battery module. Background Art

[0002] With the rapid increase in the production and sales of new energy vehicles, the safety issues of new energy vehicles have gradually become prominent. At present, lithium-ion batteries have become the main power source for new energy vehicles due to their long life and high energy density. However, lithium-ion batteries may cause serious safety accidents due to thermal runaway. Thermal runaway may be triggered by various lithium-ion battery abuses, such as mechanical abuse (foreign object puncture), electrical abuse (overcharging, internal short circuit), and thermal abuse (overheating). Once thermal runaway occurs, it will spread to the entire battery system, generating a large amount of heat and flammable gases, leading to further combustion and even explosion risk.

[0003] The core of electric vehicle safety accidents is thermal runaway of power batteries, which is initially triggered by thermal runaway of a single battery cell and releases a large amount of heat in a short period of time. This heat will be transferred to adjacent battery cells, causing their temperature to rise and further runaway, and even causing the thermal runaway of the entire battery module or the entire battery pack to spread. Thermal runaway is often accompanied by smoke, fire or explosion, which is extremely dangerous. Therefore, in order to ensure the safety of passengers' lives and property, it is of great significance to inhibit or delay the spread of power battery heat to ensure the safety of passengers' lives and property.

[0004] Setting up an insulation layer between battery cells is considered a feasible measure to delay the spread of thermal runaway, with the aim of delaying battery fire and buying time for personnel to escape. However, studies have shown that due to the accumulation of heat in the battery pack, it is difficult to completely eliminate the risk of thermal diffusion of the battery pack by insulation alone. It is necessary to use heat conduction or dissipation measures to remove the heat inside the battery pack to effectively prevent the battery pack from catching fire. Many battery packs are equipped with liquid cooling systems, which usually regulate the battery temperature as part of the battery thermal management system and can conduct heat when thermal runaway occurs. The combination of thermal conduction and insulation can more effectively deal with the risk of thermal diffusion of batteries. However, setting up an insulation layer between battery cells will lead to a lower space utilization rate in the battery pack, affecting the energy density of the battery. The thickness of the insulation layer should balance the contradiction between battery safety and energy density, ensuring that heat diffusion does not occur, while maximizing the utilization rate of the battery pack and increasing the range of electric vehicles.

[0005] Although there are many methods and ideas for battery pack thermal runaway diffusion protection, they are all given qualitatively, without quantitative results for the thickness of the thermal insulation layer, and cannot effectively guide the development of specific protection systems. When designing the thickness of the thermal insulation layer, in order to balance the contradiction between battery safety and energy density, a large number of battery pack thermal runaway fire tests are often required, resulting in a long development cycle and high development costs. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a method for determining the thickness of the thermal insulation layer in a liquid-cooled battery module. The method provided by the present invention can determine the thickness of the thermal insulation layer without heat diffusion.

[0007] The present invention provides a method for determining the thickness of a heat insulation layer in a liquid-cooled battery module, comprising the following steps:

[0008] Performing an ARC test on the battery cell to obtain characteristic parameters of thermal runaway of the battery cell; the characteristic parameters of thermal runaway of the battery cell include self-heating temperature, thermal runaway starting temperature, thermal runaway maximum temperature and total heat generation;

[0009] Conduct thermal diffusion modeling of liquid-cooled battery modules, obtain a 3D model of the liquid-cooled battery module, perform thermal runaway diffusion simulation on the 3D model of the liquid-cooled battery module, and obtain the minimum convection coefficient of the liquid cooling system without thermal diffusion under multiple groups of thermal insulation layers of different thicknesses according to the thermal runaway characteristic parameters and thermodynamic parameters of the battery cell given the material type of the thermal insulation layer;

[0010] The minimum liquid cooling system convection coefficient and the corresponding insulation layer thickness are fitted, and the insulation layer thickness at which heat diffusion does not occur is obtained based on the fitted curve.

[0011] Preferably, the liquid-cooled battery module 3D model includes a liquid cooling plate and a battery cell assembly abutting against the liquid cooling plate;

[0012] The battery cell assembly includes a plurality of battery cells, and adjacent battery cells are separated by a heat insulation layer; a flow channel is arranged in the liquid cooling plate, and the flow channel is filled with cooling liquid.

[0013] Preferably, the liquid-cooled battery module 3D model also includes a heating plate.

[0014] Preferably, the material types of the thermal insulation layer include composite phase change thermal insulation layer, nano ceramic fiber or glass fiber aerogel.

[0015] Preferably, the modeling is performed in multi-physics field simulation software, and the multi-physics field simulation software includes ANSYS Fluent or COMSOL Multiphysics.

[0016] Preferably, the thermodynamic parameters include the material, density, specific heat capacity and thermal conductivity of the pole piece, shell and core of the battery cell, heating plate, liquid cooling plate, coolant and insulation layer.

[0017] Preferably, the thermal runaway diffusion simulation follows the following formula:

[0018]

[0019] Among them, ρ, C p, λ represent the density, specific heat capacity and thermal conductivity of the solid material respectively, λ x ,λ y ,λ z Represents the thermal conductivity in different directions, q v Indicates the heat output per unit volume.

[0020] Preferably, the convection coefficient of the liquid cooling system follows the following formula:

[0021] Nu=hL / k,

[0022] Where k is the thermal conductivity, h is the convection coefficient, L is the characteristic length, Nu is the Nusselt number, Nu = 0.023*Re^0.8*Pr^0.33, Re is the Reynolds number, and Pr is the Prandtl number.

[0023] Preferably, the fitting is performed using Matlab, and the curve obtained by the fitting is d=5.108h -0.08422 -2.711.

[0024] Preferably, the curve obtained by fitting has the convection coefficient of the liquid cooling system as the horizontal coordinate and the thickness of the insulation layer as the vertical coordinate.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a method for determining the thickness of a heat insulation layer in a liquid-cooled battery module, comprising the following steps:

[0027] Performing an ARC test on the battery cell to obtain characteristic parameters of thermal runaway of the battery cell; the characteristic parameters of thermal runaway of the battery cell include self-heating temperature, thermal runaway starting temperature, thermal runaway maximum temperature and total heat generation;

[0028] Conduct thermal diffusion modeling of liquid-cooled battery modules, obtain a 3D model of the liquid-cooled battery module, perform thermal runaway diffusion simulation on the 3D model of the liquid-cooled battery module, and obtain the minimum convection coefficient of the liquid cooling system without thermal diffusion under multiple groups of thermal insulation layers of different thicknesses according to the thermal runaway characteristic parameters and thermodynamic parameters of the battery cell given the material type of the thermal insulation layer;

[0029] The minimum liquid cooling system convection coefficient and the corresponding insulation layer thickness are fitted, and the insulation layer thickness at which heat diffusion does not occur is obtained based on the fitted curve.

[0030] The present invention, through theoretical simulation, reveals the relationship between the thickness of the thermal insulation layer and the thermal conductivity (convection coefficient) of the liquid cooling system in the system design under the premise that thermal runaway diffusion does not occur, and can obtain the thickness of the thermal insulation layer that will not cause thermal diffusion, shorten the development cycle, and save development costs. The method for determining the thickness of the thermal insulation layer of the present invention can provide guidance for the thermal diffusion safety design of liquid-cooled batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 Flow chart for determining the thickness of the thermal insulation layer for an embodiment;

[0033] Figure 2 This is the ARC experimental device and schematic diagram;

[0034] Figure 3 This is the temperature-time relationship diagram of thermal runaway of the battery cell;

[0035] Figure 4 It is a 3D model of the liquid-cooled battery module;

[0036] Figure 5 It is the critical diagram of thermal runaway risk;

[0037] Figure 6 Provide guidance for battery thermal diffusion safety design;

[0038] Figure 7 This is a “temperature-time” relationship diagram of thermal runaway of a battery cell obtained in the example. DETAILED DESCRIPTION

[0039] The present invention provides a method for determining the thickness of a heat insulation layer in a liquid-cooled battery module, comprising the following steps:

[0040] Performing an ARC test on the battery cell to obtain characteristic parameters of thermal runaway of the battery cell; the characteristic parameters of thermal runaway of the battery cell include self-heating temperature, thermal runaway starting temperature, thermal runaway maximum temperature and total heat generation;

[0041] Conduct thermal diffusion modeling of liquid-cooled battery modules, obtain a 3D model of the liquid-cooled battery module, perform thermal runaway diffusion simulation on the 3D model of the liquid-cooled battery module, and obtain the minimum convection coefficient of the liquid cooling system without thermal diffusion under multiple groups of thermal insulation layers of different thicknesses according to the thermal runaway characteristic parameters and thermodynamic parameters of the battery cell given the material type of the thermal insulation layer;

[0042] The minimum liquid cooling system convection coefficient and the corresponding insulation layer thickness are fitted, and the insulation layer thickness at which heat diffusion does not occur is obtained based on the fitted curve.

[0043] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0044] Figure 1 A flow chart for determining the thickness of the thermal insulation layer for the present invention is provided. First, a battery cell ARC test is performed to obtain the characteristic parameters of thermal runaway of the battery cell. Then, 3D modeling and thermal runaway diffusion simulation are performed to obtain the convection coefficient of the liquid cooling system when no heat diffusion occurs at a certain insulation layer thickness. The thickness is changed to obtain multiple groups of insulation layer thicknesses and corresponding liquid cooling system convection coefficients. A fitting curve is performed to guide the design of the insulation layer thickness according to the curve.

[0045] The present invention performs an ARC test on the battery cell to obtain the characteristic parameters of thermal runaway of the battery cell; the characteristic parameters of thermal runaway of the battery cell include self-heating temperature (T1), thermal runaway starting temperature (T2), thermal runaway maximum temperature (T3) and total heat generation (Q c ).

[0046] In the present invention, the ARC test is as follows: gradually increase the ambient temperature in an adiabatic environment to induce thermal runaway of the battery, thereby obtaining the thermodynamic parameters of thermal runaway of the battery. ARC mainly follows the rule of "heating-waiting-searching" to heat the battery before thermal runaway. The resistance wire inside the wall of the calorimetric chamber raises the wall temperature, further heats the air in the calorimetric chamber, and raises the battery temperature. Thermocouples are arranged on the surface of the battery to monitor the battery temperature. When the battery temperature reaches the set target value, the resistance wire stops heating and enters the "waiting-searching stage". When the temperature rise rate of the battery is detected to reach 0.02℃ / min, it proves that the battery has entered the self-heating stage and a slight out-of-control has occurred inside. At this time, ARC adjusts the heating power of the resistance wire to keep the temperature in the calorimetric chamber consistent with the surface temperature of the battery, creating an adiabatic environment. The battery does not exchange heat with the outside world until the thermal runaway process of the battery ends, thereby truly reflecting the thermal runaway characteristics of the battery. Figure 2 This is the ARC experimental device and schematic diagram.

[0047] Figure 3 This is the "temperature-time" relationship diagram of thermal runaway of the battery cell obtained through ARC test, which includes the self-heating temperature T1, the thermal runaway starting temperature T2, the thermal runaway maximum temperature T3, and the total heat generation Q c .

[0048] The present invention performs thermal diffusion modeling of a liquid-cooled battery module to obtain a 3D model of the liquid-cooled battery module, performs thermal runaway diffusion simulation on the 3D model of the liquid-cooled battery module, and obtains the minimum convection coefficient of the liquid cooling system without heat diffusion under multiple groups of thermal insulation layers of different thicknesses according to the thermal runaway characteristic parameters and thermodynamic parameters of the battery cell given the material type of the thermal insulation layer.

[0049] In the present invention, the 3D model of the liquid-cooled battery module obtained by modeling is as follows Figure 4 As shown, it includes a liquid cooling plate, and a battery cell assembly abutting against the liquid cooling plate;

[0050] The battery cell assembly includes a plurality of battery cells, and adjacent battery cells are separated by a heat insulation layer; a flow channel is arranged in the liquid cooling plate, and the flow channel is filled with cooling liquid.

[0051] In the present invention, the liquid-cooled battery module 3D model preferably also includes a heating plate.

[0052] In the present invention, in the thermal runaway diffusion simulation: the total heat generation Q c As the basis for setting the heat source power, the heat release power after the first cell thermal runaway begins is set to a constant value W = Q c / t, t is the time taken to reach the maximum temperature (T3) after thermal runaway (T2) is triggered.

[0053] In the present invention, the material types of the thermal insulation layer preferably include composite phase change thermal insulation layer, nano ceramic fiber or glass fiber aerogel.

[0054] In the present invention, the thermodynamic parameters preferably include the material, density, specific heat capacity and thermal conductivity of the pole piece, shell and core of the battery cell, heating plate, liquid cooling plate, coolant and thermal insulation layer.

[0055] In the present invention, the modeling is preferably performed in a multi-physics simulation software, and the multi-physics simulation software preferably includes ANSYS Fluent or COMSOL Multiphysics. The control equations in the multi-physics simulation software are preferably set as follows:

[0056] The thermal runaway diffusion process needs to follow the basic principles of heat transfer:

[0057]

[0058] Among them, ρ, C p , λ represent the density, specific heat capacity and thermal conductivity of the solid material respectively, λ x ,λ y ,λ z Represents the thermal conductivity in different directions, q v Indicates the heat output per unit volume.

[0059] q v It consists of two parts, namely the heater heating power q v,h And the heat power generated by thermal runaway of the battery cell q v,c .

[0060] q v =q v,h +q v,c (2)

[0061] The heating power of the heater is considered to be constant. After the first cell experiences thermal runaway, the heating stops immediately. The control equation is as follows:

[0062]

[0063] Among them U h ,I h Respectively represent the voltage and current input to the heater from the DC power supply, V h represents the volume of the heater, maxT(Cell1) represents the maximum temperature of the first battery next to the heater, and T2 represents the critical triggering temperature of battery thermal runaway measured in the ARC test.

[0064] Thermal runaway heat power q v,c Calculate according to formula (4)

[0065]

[0066] Where V jr Indicates the volume of the battery cell, Q c It represents the total heat energy released by the battery cell during thermal runaway. u represents the normalized concentration. It is equal to 1 before the battery starts to self-heat. It gradually becomes smaller during the thermal runaway process. When all the energy of the battery is released, u is equal to 0.

[0067]

[0068]

[0069] Where V jr represents the volume of the battery cell, T1 represents the starting temperature of abnormal heating of the battery in the ARC test, also referred to as the initial temperature of self-heating. Among them, T3 represents the highest temperature during thermal runaway, ρ jr and C p,jr Respectively represent the density and specific heat capacity of the battery cell, M ARC Indicates different working modes of ARC. ARC It is equal to 0 when the battery cell is not generating heat and equal to 1 in other modes.

[0070]

[0071] In formula (4), represents the energy release rate, and the calculation method is shown in formula (7). Represents the temperature change rate inside the battery obtained by ARC test. When the temperature is lower than T1, the self-heating power of the battery cell is too low to be detected. Therefore, this model is used to calculate only the heating of the battery from T1 to T2. When the temperature reaches the trigger temperature T2 of thermal runaway, the remaining energy is released at a constant power C, and the value of C can be obtained by fitting the ARC test data.

[0072] For the liquid cooling system, the relevant parameters are calculated as follows:

[0073]

[0074] In the formula, R e ,ρ c ,u c ,D h ,μ c They represent the Reynolds number of the liquid cooling system, the density of the coolant, the average velocity of the coolant in the cooling plate, the hydraulic diameter, and the dynamic viscosity. Dynamic viscosity μ c , hydraulic diameter D h It can be calculated by formula (9) (10).

[0075]

[0076]

[0077] In formula (9), represents the volume flow rate of the coolant, in equations (9) and (10), δ cp ,w cp Respectively represent the thickness and width of the coolant in the cooling plate. For example, if it is used as a cooling medium, the maximum volume flow rate is 7.8L / min, and the laminar flow R e It is 1277.

[0078] The flow of the coolant is described by the Navier-Stokes (NS) equations. Assuming that water is incompressible and the flow field in the cooling plate is constant, the simplified NS equations are as follows.

[0079]

[0080]

[0081]

[0082]

[0083]

[0084] where u c ,v c ,w c They represent the speed in the x, y, and z directions respectively, p represents the pressure, T represents the coolant temperature, and λ c represents the thermal conductivity of the coolant, S T represents the viscous dissipation parameter.

[0085] Boundary conditions in the model, including convection, radiation, and thin layers,

[0086] q conv =h·(Te -T)(16)

[0087]

[0088] Where h is the convection coefficient, T e represents the external ambient temperature, ε represents the surface emissivity, σ represents the Stefan-Boltzmann constant, q conv ,q rad represent convective heat transfer and radiative heat transfer respectively.

[0089] In the present invention, the convection coefficient of the liquid cooling system is mainly related to the type and flow rate of the coolant. At present, the liquid cooling system of the thermal management system of the automotive power battery mostly adopts flat plate liquid cooling. The convection heat transfer coefficient under the condition of flat plate liquid cooling is calculated using Nu=hL / k, where k is the thermal conductivity, h is the convection heat transfer coefficient (convection coefficient), L is the characteristic length, Nu is the Nusselt number, Nu=0.023*Re^0.8*Pr^0.33, Re is the Reynolds number, and Pr is the Prandtl number.

[0090] The present invention fits the minimum liquid cooling system convection coefficient and the corresponding insulation layer thickness, and obtains the insulation layer thickness at which heat diffusion does not occur based on the fitted curve.

[0091] In the present invention, the curve obtained by fitting preferably takes the convection coefficient of the liquid cooling system as the horizontal coordinate and the thickness of the thermal insulation layer as the vertical coordinate; the fitting is preferably performed using MATLAB, and the curve obtained by fitting is preferably d = 5.108h -0.08422 -2.711. In a specific embodiment, the fitted curve is as follows Figure 5 As shown, the upper right corner of the curve indicates the region where heat diffusion does not occur, and the lower left corner indicates the region where heat diffusion occurs.

[0092] The thickness of the thermal insulation layer can characterize the ability to delay heat diffusion between batteries, while the functional optimization of the liquid cooling system can represent the heat dissipation capacity of the module. The confirmation method of the present invention can be further promoted to guide the safe design of batteries.

[0093] The present invention obtains the critical line (curve) of thermal diffusion by fitting simulation data as follows: Figure 6 As shown, the upper right shaded area includes a safe area that is not affected by heat diffusion. Serial numbers 1 to 4 represent four sub-domains with unsafe designs. Parts 1 to 3 have higher risks. Part 4 has a lower risk than areas 1 to 3 by considering the synergistic effect of insulation and heat dissipation, and can improve the battery energy density. The battery thermal runaway protection design should be as close to the curve as possible.

[0094] The present invention is aimed at a battery module equipped with a liquid cooling system and a heat insulating sheet, and its components include: a barrier layer with heat insulating properties (glass fiber or aerogel), a liquid cooling system (a radiator with circulating coolant), and a battery module composed of multiple battery cells; the present invention can guide the thermal protection design of the liquid-cooled battery module, shorten the development process and save development costs.

[0095] In order to further illustrate the present invention, the method for determining the thickness of the thermal insulation layer in the liquid-cooled battery module provided by the present invention is described in detail below in combination with the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0096] Example 1

[0097] Take a 60Ah ternary lithium-ion soft pack battery as an example

[0098] 1. Carry out ARC experiment (accelerated calorimetry), Figure 7 The "temperature-time" relationship diagram of the thermal runaway of the battery obtained in the embodiment, and the measured characteristic temperature of the thermal runaway of the battery are shown in the following Table 1:

[0099] Table 1 Battery thermal runaway characteristic temperature

[0100] <![CDATA[T1 (Initial temperature of self-heating)]]> <![CDATA[T2 (Thermal runaway trigger temperature)]]> <![CDATA[T3 (Highest temperature of thermal runaway)]]> 84℃ 147℃ 660℃

[0101] The total heat generated by the battery is calculated to be 666386J according to the following formula:

[0102] Q=cm(T3-T0)

[0103] In the formula, Q is the total heat generation, c is the specific heat capacity of the battery, m is the battery mass, T3 represents the maximum temperature of thermal runaway of the battery, and T0 is the initial ambient temperature.

[0104] 2. Establish the following in the multi-physics simulation software comsol Figure 4 The thermodynamic simulation model shown (Q is used as the basis for setting the power of the heat source in the simulation model. The heat release power after the start of thermal runaway of the first battery cell in the simulation model is set to a constant value W=Q / t, and t is the time taken to reach the highest temperature after the thermal runaway is triggered). The heat generation of the ARC experimental battery cell is used as the heat source, and the grid is divided for simulation. Below the model is a cold plate with built-in flow channels and coolant; starting from the left, the first battery cell is the thermal runaway triggering battery cell, followed by insulation layer 1, battery cell 2, insulation layer 2, battery cell 3, insulation layer 3, and battery cell 4 (the insulation layer on the far right of the figure does not exist). The physical properties of the battery cells and the thermal conductivity of the insulation layer are shown in Table 2 below:

[0105] Table 2 Physical parameters of battery cells and thermal conductivity of insulation layer

[0106] Component Name Material <![CDATA[ρ(kg·m 3 )]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[c <h2 style=";text-align:left;direction:ltr"> p <h2 style=";text-align:left;direction:ltr"> (J·kg<h2 style=";text-align:left;direction:ltr"> -1 <h2 style=";text-align:left;direction:ltr"> K<h2 style=";text-align:left;direction:ltr"> -1 <h2 style=";text-align:left;direction:ltr"> )]]><h2 style=";text-align:left;direction:ltr"> <![CDATA[λ(W·m -1 ·K -1 )]]> Heater Stainless steel 7850 475 44.5 shell aluminum 2700 900 160 Kernel NCM622 2000 1250 <![CDATA[λ x =λ z =21,λ y =0.72]]> negative electrode Nickel-plated copper 8522 385 146 positive electrode aluminum 2700 900 160

[0107] In the table, ρ is the density of the battery cell, C p is the specific heat capacity of the battery cell; λ is the thermal conductivity of the battery cell in all directions.

[0108] Table 3 below shows the parameters of the selected insulation layer materials:

[0109] Table 3 Parameters of thermal insulation materials

[0110]

[0111] Divide the grid, perform simulation, and observe whether the model has thermal runaway propagation. Find a critical point where thermal runaway propagation occurs. Note the thickness d at this time, and calculate the convective heat transfer coefficient of the liquid cooling plate. In the modeling analysis, the equivalent convection coefficient h can be used to replace the convection coefficient of the liquid cooling plate. The larger h is, the higher the flow rate of liquid cooling. In the specific heat spread test, Nu=hL / k can be used to calculate the convective heat transfer coefficient, where the thermal conductivity is k, h is the convective heat transfer coefficient, L is the characteristic length, Nu is the Nusselt number, Nu=0.023*Re^0.8*Pr^0.33, Re is the Reynolds number, and Pr is the Prandtl number. Then change the values ​​of d and h, find multiple critical points, and fit them through matlab. Table 4 shows the critical points where thermal runaway does not occur after multiple simulations:

[0112] Table 4 Critical points where thermal runaway does not occur after multiple simulations

[0113]

[0114] When other types of thermal insulation materials are used, their dh curves can also be obtained by this method. A database is established using the thermal insulation performance data of various materials to guide system design.

[0115] The relationship diagram drawn by fitting of sample 1 (nano ceramic fiber) is as follows Figure 5 As shown, d = 5.108h -0.08422 -2.711, so that when different insulation layer battery modules of the same liquid cooling system are used in the future, the thickness of the insulation material at which no heat spread occurs can be known, which is convenient for formulating the thermal runaway management strategy of the liquid cooling system.

[0116] The present invention provides a method for determining the thickness of the thermal insulation layer of a liquid-cooled battery pack, which guides the safety design of the battery pack from a microscopic level. The battery pack includes multiple battery cells and a liquid cooling device, and a thermal insulation layer is arranged between each battery cell; the battery cell stores electricity; when a cell has thermal runaway, the thermal insulation layer blocks the heat generated by the thermal runaway of each battery cell, and the liquid cooling device conducts the heat away to prevent the heat from spreading in the battery pack, thereby reducing the temperature inside the battery pack and preventing the battery pack from catching fire, thereby suppressing the thermal runaway of the battery pack.

[0117] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for determining the thickness of a thermal insulation layer in a liquid-cooled battery module, characterized in that: The following steps are involved: Performing an ARC test on the battery cell to obtain characteristic parameters of thermal runaway of the battery cell; the characteristic parameters of thermal runaway of the battery cell include self-heating temperature, thermal runaway starting temperature, thermal runaway maximum temperature and total heat generation; Conduct thermal diffusion modeling of liquid-cooled battery modules, obtain a 3D model of the liquid-cooled battery module, perform thermal runaway diffusion simulation on the 3D model of the liquid-cooled battery module, and obtain the minimum convection coefficient of the liquid cooling system without thermal diffusion under multiple groups of thermal insulation layers of different thicknesses according to the thermal runaway characteristic parameters and thermodynamic parameters of the battery cell given the material type of the thermal insulation layer; The minimum liquid cooling system convection coefficient and the corresponding insulation layer thickness are fitted, and the insulation layer thickness at which heat diffusion does not occur is obtained based on the fitted curve.

2. The determination method according to claim 1, characterized in that: The liquid-cooled battery module 3D model includes a liquid cooling plate and a battery cell assembly abutting against the liquid cooling plate; The battery cell assembly includes a plurality of battery cells, and adjacent battery cells are separated by a heat insulation layer; a flow channel is arranged in the liquid cooling plate, and the flow channel is filled with cooling liquid.

3. The determination method according to claim 2, characterized in that: The liquid-cooled battery module 3D model also includes a heating plate.

4. The determination method according to claim 1, characterized in that: The material types of the thermal insulation layer include composite phase change thermal insulation layer, nano ceramic fiber or glass fiber aerogel.

5. The determination method according to claim 1 or 4, characterized in that: The modeling is performed in multi-physics simulation software, which includes ANSYS Fluent or COMSOL Multiphysics.

6. The determination method according to claim 3, characterized in that: The thermodynamic parameters include the material, density, specific heat capacity and thermal conductivity of the battery cell's pole piece, shell and core, heating plate, liquid cooling plate, coolant and thermal insulation layer.

7. The determination method according to claim 1, characterized in that: The thermal runaway diffusion simulation follows the following formula: Among them, ρ, C p , λ represent the density, specific heat capacity and thermal conductivity of the solid material respectively, λ x ,λ y ,λ z Represents the thermal conductivity in different directions, q v Indicates the heat output per unit volume.

8. The determination method according to claim 1, characterized in that: The convection coefficient of the liquid cooling system follows the following formula: Nu=hL / k, Where k is the thermal conductivity, h is the convection coefficient, L is the characteristic length, Nu is the Nusselt number, Nu = 0.023*Re^0.8*Pr^0.33, Re is the Reynolds number, and Pr is the Prandtl number.

9. The determination method according to claim 1, characterized in that: The fitting is performed using Matlab, and the curve obtained by the fitting is d=5.108h -0.08422 -2.

711.

10. The determination method according to claim 1 or 9, characterized in that: The curve obtained by fitting has the convection coefficient of the liquid cooling system as the abscissa and the thickness of the thermal insulation layer as the ordinate.

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