High-capacity energy storage battery thermal runaway propagation simulation model construction method

Abstract

The invention discloses a method for constructing a thermal runaway propagation simulation model of a high-capacity energy storage battery. The method comprises the following steps: S1, acquiring an anisotropic heat transfer coefficient of the high-capacity energy storage battery by using a heat transfer coefficient tester; s2, testing the specific heat capacity of the battery by using an adiabatic calorimeter; s3, testing the internal composition of the battery by using a differential scanning calorimeter to obtain basic thermal parameter data such as active substance decomposition reaction enthalpy and carbon content per unit volume; s4, establishing a geometric model of the battery according to the specification, size and internal composition of the battery; s5, establishing a simulation heat transfer model by utilizing the anisotropic heat conductivity coefficients of the battery obtained by testing in the step S1 and the step S2; s6, according to the internal thermal runaway side reaction equation of the battery and the thermal parameters obtained in the step S1, simulation software is used for conducting simulation modeling on the battery; and S7, expanding the single battery simulation model into a battery pack thermal runaway propagation model, researching the thermal runaway propagation behavior of the battery, and further predicting the thermal behavior of battery propagation in a real environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery thermal runaway simulation, and in particular relates to a method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery. Background Art

[0002] Batteries are at risk of thermal runaway under normal or abnormal operating conditions, that is, a series of violent exothermic reactions occur inside the battery, causing the temperature to rise sharply, leading to fire and explosion accidents. Compared with power batteries, energy storage lithium batteries have higher capacity, thermal runaway releases more energy, and heat spreads more seriously. On the one hand, the heat generated by the battery during long-term charging and discharging will accelerate battery aging and capacity decay, affect battery performance, and increase the risk of thermal runaway of the battery; on the other hand, continuous heat accumulation or extreme abuse conditions will stimulate a chain exothermic reaction inside the battery, causing the battery to thermally runaway and release a large amount of heat and flammable gases. The heat released by the thermal runaway of the battery spreads rapidly to the surrounding batteries through the outer shell, electrode connectors, flame radiation, etc., causing the thermal runaway of the battery module to spread, and then causing serious accidents such as fire and explosion in the entire system. At present, the risk of thermal runaway has seriously restricted the development of large-scale energy storage power stations.

[0003] The heat conduction equation in the existing model does not include the heat source of the SEI film decomposition during the thermal runaway process inside the battery. To address this deficiency, this patent proposes a three-dimensional battery thermal runaway propagation model that can more accurately reflect the heat propagation characteristics of the battery thermal runaway process, providing important support for the development of prevention technology for thermal runaway propagation of large-capacity energy storage batteries. Summary of the invention

[0004] In view of the above problems, the present invention proposes a method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery based on the thermal runaway heat generation reaction mechanism and the thermal runaway propagation mechanism of the battery.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery comprises the following steps:

[0007] Step S1: using a heat transfer coefficient tester to obtain the anisotropic heat transfer coefficient of a large-capacity energy storage battery;

[0008] Step S2: using an adiabatic calorimeter to test the specific heat capacity of the battery;

[0009] Step S3: using a differential scanning calorimeter to test the internal composition of the battery and obtain basic thermal parameter data such as the decomposition reaction enthalpy of the active material and the carbon content per unit volume;

[0010] Step S4: Establishing a geometric model of the battery according to the size and internal composition of the battery;

[0011] Step S5: Establishing a simulation heat transfer model using the anisotropic thermal conductivity of the battery obtained by testing in steps S1 and S2;

[0012] Step S6: Based on the thermal runaway side reaction equation inside the battery and the thermal parameters obtained in step S1, the battery is simulated and modeled using simulation software, a thermal runaway propagation model of the battery pack is established, and the heat generation and thermal runaway characteristics of the battery are studied;

[0013] Step S7: The verified single-battery simulation model is expanded into a battery pack thermal runaway propagation model to study the thermal runaway propagation behavior of the battery, and then predict the thermal behavior of the battery propagation in a real environment.

[0014] Furthermore: To simplify the calculation, the battery model established in step S4 needs to be homogenized.

[0015] Furthermore, in the heat transfer model constructed in step S5, while the battery undergoes convective heat exchange with the external environment during the thermal runaway process, the internal heat source has the most important influence on the heat generation process of the battery.

[0016] The heat transfer equation inside the battery is as follows:

[0017]

[0018] In the formula, ρ, C p and Q represent the battery density, specific heat capacity and heat generation rate when the battery is in thermal runaway. represent the thermal conductivity of the battery in each direction. ∑Q tot is the heat source term for correcting the internal heat conduction equation.

[0019] Further: For the heat source term ∑Q tot During the battery thermal runaway process, the chemical heat mainly comes from side reactions.

[0020] The side reactions involved in step S6 take into account the heat generated by the exothermic breakdown of components such as SEI, anode, cathode electrolyte and ISC. In order to establish the model, the energy of the lumped mass is conserved, and the TR phenomenon simulated using the lumped model (i.e., 0-D) can be mathematically expressed as:

[0021]

[0022] Among them, V cell is the battery volume, ρ jr is the density, C jr is the heat capacity, is the net heat production, is the convective heat transfer, is the amount of radiant heat transferred.

[0023]

[0024] in, The heat released by the exothermic breakdown reaction of the solid electrolyte interphase layer, The heat generated by the negative electrode's exothermic breakdown. The heat generated by the exothermic breakdown of the positive electrode, The heat generated by the exothermic breakdown of the electrolyte, It is the electrical energy converted into heat during the internal short circuit (i.e. short circuit), is the heat generated by the current. The heat released due to the exothermic decomposition of a component depends on the decomposition rate of that component. Therefore, in generalized form, it is expressed as:

[0025]

[0026] Where m is the mass of the component and H is the exothermic decomposition enthalpy of the component. The decomposition rate of the component also depends on the concentration of lithium content in the component and the battery temperature, and therefore follows the Arrhenius equation. The generalized decomposition rate is expressed as:

[0027]

[0028] Where x is the dimensionless concentration, A is the frequency factor, and E is the activation energy. When the battery temperature reaches T 1 Around 2000 ℃, the solid electrolyte interface (SEI) decomposition process begins, and the anode reacts with the electrolyte. In this process, the exothermic reaction involved is relatively limited, and the temperature rise rate is It is linearly related to temperature and can be written as:

[0029]

[0030] Where a and b are the slope and intercept of the fitting curve, respectively. The total energy released by the exothermic chemical reaction during TR is expressed as:

[0031] ΔH TR =m bat c p,bat (T 3 -T 1 )

[0032] Among them, m bat is the mass of the battery, c p,bat is the specific heat capacity of the battery, T 3 is the highest temperature of the battery during the TR process, T 1 is the temperature at which the battery loses thermal stability. The heat generation rate of the TR process can be expressed as:

[0033]

[0034] Among them, c chem represents the dimensionless parameter representing the TR process, is the reaction rate. When the battery temperature reaches about 90°C, the SEI film of the battery begins to decompose, and the decomposition side reaction will generate heat to continue to increase the battery temperature. Therefore, at 90°C, the decomposition reaction of the battery SEI film serves as the basis for triggering battery thermal runaway. The heat generation rate equation of the SEI film decomposition reaction is:

[0035] Q SEI =H SEI W SEI R SEI

[0036] The reaction rate involved in the chemical reaction kinetics equation is:

[0037]

[0038] Among them, A SEI is the frequency factor of SEI film structure type A; E a,SEI is the activation energy of the SEI film structure reaction, k is the Boltzmann constant, when the battery temperature rises to about 120°C, the negative electrode begins to contact the electrolyte, and the lithium-embedded carbon of the negative electrode reacts exothermically with the electrolyte. The heat generation rate equation for the exothermic reaction between the negative electrode and the electrolyte is:

[0039] Q ne =H ne W ne R ne

[0040] The reaction rate involved in the chemical reaction kinetics equation is:

[0041]

[0042] Among them, c ne is the dimensionless quantity of lithium ion content in the negative electrode carbon layer, R ne is the frequency factor of the negative electrode material R type, A ne is the frequency factor of negative electrode material type A, E a,ne is the activation energy of the reaction of the negative electrode material, kB is the Boltzmann constant, t SEI is the time for SEI film structure reaction, m ne C ne When the battery temperature rises to 180°C, the positive electrode active material reacts with the electrolyte to generate heat. This process will produce oxygen, accelerate the thermal runaway process of the battery, and release a large amount of heat. The heat generation rate equation for the exothermic reaction between the positive electrode and the electrolyte is:

[0043] Q pe =H pe Wpe R pe

[0044] The reaction rate involved in the chemical reaction kinetics equation is:

[0045]

[0046] Among them, c pe is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode and the positive electrode, R pe is the frequency factor of the positive electrode material R type, A pe is the frequency factor of positive electrode material type A, H pe is the heat generation rate of the positive electrode material reaction, E a,pe is the activation energy of the reaction of the positive electrode material, k is the Boltzmann constant, m pe is the activation energy of α(-). In the early stage of thermal runaway, the gas production inside the battery mainly comes from the decomposition and regeneration of SEI and the evaporation of electrolyte. The solid electrolyte interface (SEI) has metastable characteristics and generally decomposes exothermically at 80-120°C. The heat dissipated when the internal mixed gas is exhausted is:

[0047]

[0048] Among them, M ele is the molar mass of the electrolyte, H vap is the evaporation enthalpy of the electrolyte, C ele is the gas specific heat of the electrolyte under constant volume conditions, and the molar mass and constant volume specific heat of the gas generated by SEI decomposition and regeneration are expressed as M g and C g (g = SEI d ,SEI r ). When the temperature reaches 200 degrees Celsius, the electrolyte begins to decompose and burn, accelerating the entire thermal runaway process. After the electrolyte decomposes, a large amount of heat is released. The heat generation rate equation for the decomposition reaction of the electrolyte is:

[0049] Q e =H e W e R e

[0050] The reaction rate involved in the chemical reaction kinetics equation is:

[0051]

[0052] Among them, c e is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode and the positive electrode, R e is the frequency factor of the positive electrode material R type, A e is the frequency factor of positive electrode material type A, W eis the carbon content per unit volume of the positive electrode material, H e is the heat generation rate of the positive electrode material reaction, E a,e is the activation energy of the reaction of the positive electrode material; R is the universal gas constant.

[0053] Furthermore, under normal conditions, the source term ∑Q of the heat conduction equation tot =0; During thermal runaway, ∑Q tot Then it is equal to H i W i R i , i is expressed as sei, ne, pe or ele.

[0054] Furthermore, when the battery reaches different temperatures, the reaction rates of the chemical reaction kinetic equations at the corresponding stages are as follows:

[0055] S61: Use a boundary heat source to act on one side of the battery to increase its temperature to a thermal runaway trigger temperature;

[0056] S62: Raise the temperature of the battery to 90°C, so that the SEI film of the battery begins to decompose, and the battery begins to undergo a self-heating reaction, and record the average temperature of the battery and the heat generation rate of the side reaction;

[0057] S63: The battery temperature continues to rise to 120°C, the negative electrode active material of the battery reacts with the electrolyte, continues to release heat, and the average temperature of the battery and the heat generation rate of the side reaction are recorded;

[0058] S64: The battery temperature continues to rise to 180°C, the positive electrode active material of the battery reacts with the electrolyte, continues to release heat, and the average temperature of the battery and the heat generation rate of the side reaction are recorded;

[0059] S65: The battery temperature continues to rise until the electrolyte decomposes and burns, releasing a large amount of heat. The average temperature of the battery and the heat generation rate of the side reactions are recorded.

[0060] Furthermore, in step S7, the traditional single-battery heat transfer simulation model constructed by step S6 is also applicable to the battery pack heat transfer simulation model. A boundary heat source is set on only one battery to cause thermal runaway, so that the thermal runaway propagates from this battery and induces thermal runaway in other batteries. Probes are added to record the temperature changes of each battery.

[0061] The beneficial effects of the present invention are:

[0062] The present invention establishes a thermal runaway propagation simulation model of the battery according to the thermal runaway reaction equation of the battery, and simulates the thermal runaway of the battery and the heat transfer conditions of the thermal runaway propagation process in the actual environment through simulation software. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1The geometric model and mesh division diagram of the single battery;

[0064] Figure 2 This is the temperature cloud diagram of the thermal runaway process of a single 300Ah battery;

[0065] Figure 3 It is the temperature curve diagram of thermal runaway of single battery;

[0066] Figure 4 This is the temperature cloud diagram of the battery pack thermal runaway propagation model;

[0067] Figure 5 This is the temperature curve of the battery pack thermal runaway propagation model. DETAILED DESCRIPTION

[0068] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] A method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery comprises the following steps:

[0070] Step S1: using a heat transfer coefficient tester to obtain the anisotropic heat transfer coefficient of a large-capacity energy storage battery;

[0071] Step S2: using an adiabatic calorimeter to test the specific heat capacity of the battery;

[0072] Step S3: using a differential scanning calorimeter to test the internal composition of the battery and obtain basic thermal parameter data such as the decomposition reaction enthalpy of the active material and the carbon content per unit volume;

[0073] Step S4: According to the size and internal composition of the battery, a geometric model of the battery is established, and meshing is performed, and the established battery model is homogenized. Figure 1 As shown, Figure 1 (a) is the battery geometry model, and (b) is the battery mesh model.

[0074] Step S5: Establish a simulation heat transfer model using the anisotropic thermal conductivity of the battery obtained by testing in steps S1 and S2.

[0075] In the constructed heat transfer model, while the battery undergoes convective heat exchange with the external environment during thermal runaway, the internal heat source has the most important influence on the heat generation process of the battery; the heat transfer equation inside the battery is as follows:

[0076]

[0077] In the formula, ρ, C p and Q represent the battery density, specific heat capacity and heat generation rate during thermal runaway of the battery; λ x , y , z Respectively represent the thermal conductivity of the battery in the three directions of X, Y, and Z; ∑Q tot It is the heat source term for correcting the internal heat conduction equation. The heat source is the chemical heat generated by the side reactions during the thermal runaway of the battery.

[0078] Step S6: Based on the thermal runaway side reaction equation inside the battery and the thermal parameters obtained in step S1, the battery is simulated and modeled using simulation software, a thermal runaway propagation model of the battery pack is established, and the heat generation and thermal runaway characteristics of the battery are studied.

[0079] The specific steps include:

[0080] Step S61: using a boundary heat source to act on one side of the battery to raise its temperature to a thermal runaway triggering temperature;

[0081] Step S62: Raise the temperature of the battery to 90°C, so that the SEI film of the battery begins to decompose and the battery begins to undergo a self-heating reaction, and record the average temperature of the battery and the heat generation rate of the side reaction;

[0082] Step S63: the battery temperature continues to rise to 120°C, the negative electrode active material of the battery reacts with the electrolyte, continues to release heat, and the average temperature of the battery and the heat generation rate of the side reaction are recorded;

[0083] Step S64: the battery temperature continues to rise to 180°C, the positive electrode active material of the battery reacts with the electrolyte, continues to release heat, and the average temperature of the battery and the heat generation rate of the side reaction are recorded;

[0084] Step S65: The battery continues to heat up until the electrolyte decomposes and burns, releasing a large amount of heat, and the average temperature of the battery and the heat generation rate of the side reactions are recorded.

[0085] 5. A method for constructing a simulation model of thermal runaway propagation of a large-capacity energy storage battery according to claim 4, characterized in that in the step S6, the side reactions involved include the heat generated by the melting and exothermic breakdown of the solid electrolyte interface film SEI, the anode, the cathode electrolyte and the diaphragm; based on the law of conservation of energy, a lumped model is established to simulate the thermal runaway phenomenon, and its expression is:

[0086]

[0087] Among them, V cell is the battery volume, ρ jr is the battery density, C jris the heat capacity, is the net heat production, is the convective heat transfer, is the amount of radiant heat transferred;

[0088] in The net heat generation phase is calculated simultaneously as follows:

[0089]

[0090] in, The heat released by the exothermic breakdown reaction of the solid electrolyte interphase layer, The heat generated by the negative electrode's exothermic breakdown. The heat generated by the exothermic breakdown of the positive electrode, The heat generated by the exothermic breakdown of the electrolyte, It is the electrical energy converted into heat during the short circuit process inside the battery. is the heat generated by the current.

[0091] 6. A method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 5, characterized in that the heat released due to the exothermic decomposition of the component depends on the decomposition rate of the component, so in a generalized form, it is expressed as:

[0092]

[0093] Where m is the mass of the component, and H is the exothermic decomposition enthalpy of the component. The decomposition rate of the component also depends on the concentration of lithium content in the component and the battery temperature, and therefore follows the Arrhenius formula. The generalized decomposition rate can be expressed as:

[0094]

[0095] Where x is the dimensionless concentration, A is the frequency factor, E is the activation energy, and k is the Boltzmann constant.

[0096] When the battery temperature reaches T 1 Around 50 ℃, the solid electrolyte interface phase SEI decomposition process begins, and the anode reacts with the electrolyte; in this process, the exothermic reaction involved is relatively limited, and the temperature rise rate is It is linearly related to temperature, so it can be written as:

[0097]

[0098] Where a and b are the slope and intercept of the fitting curve respectively;

[0099] The total energy released by the exothermic chemical reaction during the TR process is expressed as:

[0100] ΔHTR =m bat c p,bat (T 3 -T 1 );

[0101] Among them, m bat is the mass of the battery, c p,bat is the specific heat capacity of the battery, T 3 is the highest temperature of the battery during the TR process, T 1 is the temperature at which the battery loses thermal stability; the heat generation rate of the TR process is expressed as:

[0102]

[0103] Among them, c chem represents the dimensionless parameter representing the TR process, is the reaction rate.

[0104] When the battery reaches different temperatures, the reaction rates involved in the chemical reaction kinetics equation at the corresponding stages are as follows:

[0105] 1) When the battery temperature reaches about 90°C, the SEI film of the battery begins to decompose, and the decomposition side reaction will generate heat to continue to increase the battery temperature; therefore, at 90°C, the decomposition reaction of the battery SEI film serves as the basis for triggering the battery thermal runaway; the heat generation rate equation of the SEI film decomposition reaction is:

[0106] Q SEI =H SEI W SEI R SEI ;

[0107] The reaction rate involved in the chemical reaction kinetics equation is:

[0108]

[0109] Among them, A SEI is the frequency factor of SEI film structure type A; E a,SEI is the activation energy of SEI film structural reaction, kB is the Boltzmann constant;

[0110] 2) When the battery temperature rises to about 120°C, the negative electrode begins to contact the electrolyte, and the lithium-embedded carbon of the negative electrode reacts with the electrolyte in an exothermic reaction. The heat generation rate equation for the exothermic reaction between the negative electrode and the electrolyte is:

[0111] Q ne =H ne W ne R ne ;

[0112] The reaction rate involved in the chemical reaction kinetics equation is:

[0113]

[0114] Among them, c ne is the dimensionless quantity of lithium ion content in the negative electrode carbon layer, R ne is the frequency factor of the negative electrode material R type, A ne is the frequency factor of negative electrode material type A, E a,ne is the activation energy of the reaction of the negative electrode material, kB is the Boltzmann constant, t SEI is the time for SEI film structure reaction, m ne C ne The reaction order of

[0115] 3) When the battery temperature rises to 180°C, the positive electrode active material reacts with the electrolyte to generate heat. This process produces oxygen, accelerates the thermal runaway process of the battery, and releases a large amount of heat. The heat generation rate equation for the exothermic reaction between the positive electrode and the electrolyte is:

[0116] Q pe =H pe W pe R pe ;

[0117] The reaction rate involved in the chemical reaction kinetics equation is:

[0118]

[0119] Among them, c pe is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode and the positive electrode, R pe is the frequency factor of the positive electrode material R type, A pe is the frequency factor of positive electrode material type A, H pe is the heat generation rate of the positive electrode material reaction, E a,pe is the activation energy of the reaction of the positive electrode material, k is the Boltzmann constant, m pe is the activation energy of α(-);

[0120] In the early stage of thermal runaway, the gas production inside the battery mainly comes from the decomposition and regeneration of SEI and the evaporation of the electrolyte. The solid electrolyte interface (SEI) has metastable characteristics and generally decomposes exothermically at 80-120°C.

[0121] The heat dissipated when the internal mixed gas is exhausted is:

[0122]

[0123] Among them, M ele is the molar mass of the electrolyte, H vap is the evaporation enthalpy of the electrolyte, C eleis the gas specific heat of the electrolyte under constant volume conditions, and the molar mass and constant volume specific heat of the gas generated by SEI decomposition and regeneration are expressed as M g and C g , g = SEI d ,SEI r ;

[0124] 4) When the temperature reaches 200 degrees Celsius, the electrolyte begins to decompose and burn, accelerating the entire thermal runaway process; after the electrolyte decomposes, a large amount of heat is released; the heat generation rate equation of the electrolyte decomposition reaction is:

[0125] Q e =H e W e R e ;

[0126] The reaction rate involved in the chemical reaction kinetics equation is:

[0127]

[0128] Among them, c e is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode and the positive electrode, R e is the frequency factor of the positive electrode material R type, A e is the frequency factor of positive electrode material type A, W e is the carbon content per unit volume of the positive electrode material, H e is the heat generation rate of the positive electrode material reaction, E a,e is the activation energy of the reaction of the positive electrode material; R is the universal gas constant.

[0129] Under normal conditions, the source term ∑Q of the heat conduction equation tot =0; During thermal runaway, ∑Q tot Then it is equal to H i W i R i , i is represented by SEI, ne, pe or ele.

[0130] like Figure 2 , 3 As shown, Figure 2 This is a temperature cloud diagram of the thermal runaway process of a single 300Ah battery. The single battery is heated on one side until the battery begins to thermal runaway and then the heating is stopped. The battery will continue to heat up due to the heat released by the internal side reaction until the side reaction is completely completed. Figure 3 The temperature curve of thermal runaway of a single battery is shown in Figure 2. Figure 3 It can be seen that the battery begins to experience thermal runaway at around 110 degrees, and the battery temperature rises sharply. The battery temperature gradually decreases after the side reaction has completely occurred.

[0131] Step S7: Use the verified single-battery simulation model to expand it into a battery pack thermal runaway propagation model to study the thermal runaway propagation behavior of the battery, and then predict the thermal behavior of the battery propagation in the real environment. The traditional single-battery heat transfer simulation model constructed by step S6 in step S7 is also applicable to the battery pack heat transfer simulation model. Only a boundary heat source is set on one battery to cause thermal runaway, so that the thermal runaway propagates from this battery, inducing thermal runaway in other batteries, and probes are added to record the temperature changes of each battery. Figure 4 , 5 As shown. Among them, Figure 4 This is the temperature cloud diagram of the battery thermal runaway propagation model. It can be seen from the figure that after the heating triggers the thermal runaway of the first battery, the thermal runaway will continue to propagate to other adjacent batteries as time goes on. Figure 5 This is a temperature curve diagram of the battery thermal runaway propagation model. It can be seen from the figure that after a battery thermal runaway, heat will be transferred to the surrounding batteries, causing the surrounding battery temperature to rise, and eventually leading to the spread of thermal runaway. The present invention establishes a battery thermal runaway propagation simulation model based on the battery thermal runaway reaction equation, and simulates the heat transfer of battery thermal runaway and thermal runaway propagation process in an actual environment through simulation software.

[0132] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for constructing a simulation model of thermal runaway propagation of a large-capacity energy storage battery, characterized in that: The following steps are involved: Step S1: using a heat transfer coefficient tester to obtain the anisotropic heat transfer coefficient of a large-capacity energy storage battery; Step S2: using an adiabatic calorimeter to test the specific heat capacity of the battery; Step S3: using a differential scanning calorimeter to test the internal composition of the battery and obtain basic thermal parameter data such as the decomposition reaction enthalpy of the active material and the carbon content per unit volume; Step S4: Establishing a geometric model of the battery according to the size and internal composition of the battery; Step S5: Establishing a simulation heat transfer model using the anisotropic thermal conductivity of the battery obtained by testing in steps S1 and S2; Step S6: Based on the thermal runaway side reaction equation inside the battery and the thermal parameters obtained in step S1, the battery is simulated and modeled using simulation software, a thermal runaway propagation model of the battery pack is established, and the heat generation and thermal runaway characteristics of the battery are studied; Step S7: Expand the single-battery simulation model into a battery pack thermal runaway propagation model to study the thermal runaway propagation behavior of the battery, and then predict the thermal behavior of the battery propagation in a real environment.

2. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 1, characterized in that: The battery model established in step S4 is homogenized.

3. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 2, characterized in that: In step S5, in the constructed heat transfer model, the battery undergoes convective heat exchange with the external environment during the thermal runaway process, and the internal heat source has the most important influence on the heat generation process of the battery; the heat transfer equation inside the battery is as follows: In the formula, ρ, C p and Q represent the battery density, specific heat capacity and heat generation rate during thermal runaway of the battery; λ x , y , z Respectively represent the thermal conductivity of the battery in the X, Y, and Z directions; ∑Q tot It is the heat source term for correcting the internal heat conduction equation. The heat source is the chemical heat generated by the side reactions during the thermal runaway of the battery.

4. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 3, characterized in that: In the step S6, according to the thermal runaway side reaction equation inside the battery and the thermal parameters obtained in S1, the following steps are specifically included: Step S61: using a boundary heat source to act on one side of the battery to raise its temperature to a thermal runaway triggering temperature; Step S62: Raise the temperature of the battery to 90°C, so that the SEI film of the battery begins to decompose, and the battery begins to undergo a self-heating reaction, and record the average temperature of the battery and the heat generation rate of the side reaction; Step S63: the battery temperature continues to rise to 120°C, the negative electrode active material of the battery reacts with the electrolyte, continues to release heat, and the average temperature of the battery and the heat generation rate of the side reaction are recorded; Step S64: the battery temperature continues to rise to 180°C, the positive electrode active material of the battery reacts with the electrolyte, continues to release heat, and the average temperature of the battery and the heat generation rate of the side reaction are recorded; Step S65: The battery continues to heat up until the electrolyte decomposes and burns, releasing a large amount of heat, and the average temperature of the battery and the heat generation rate of the side reactions are recorded.

5. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 4, characterized in that: In step S6, the side reactions involved include the heat generated by the melting and exothermic breakdown of the solid electrolyte interface film SEI, the anode, the cathode electrolyte and the diaphragm; based on the energy conservation, a lumped model is established to simulate the thermal runaway phenomenon, and its expression is: Among them, V cell is the battery volume, ρ jr is the battery density, C jr is the heat capacity, is the net heat production, is the convective heat transfer, is the amount of radiant heat transferred; in The net heat generation phase is calculated simultaneously as follows: in, The heat released by the exothermic breakdown reaction of the solid electrolyte interphase layer, The heat generated by the negative electrode's exothermic breakdown. The heat generated by the exothermic breakdown of the positive electrode, The heat generated by the exothermic breakdown of the electrolyte, It is the electrical energy converted into heat during the short circuit process inside the battery. is the heat generated by the current.

6. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 5, characterized in that: The amount of heat released due to the exothermic decomposition of a component depends on the decomposition rate of that component and, therefore, in generalized form, is expressed as: Where m is the mass of the component, and H is the exothermic decomposition enthalpy of the component. The decomposition rate of the component also depends on the concentration of lithium content in the component and the battery temperature, and therefore follows the Arrhenius formula. The generalized decomposition rate can be expressed as: Where x is the dimensionless concentration, A is the frequency factor, E is the activation energy, and k is the Boltzmann constant. When the battery temperature reaches about T1, the solid electrolyte interface phase SEI decomposition process begins, and the anode reacts with the electrolyte; in this process, the exothermic reaction involved is relatively limited, and the temperature rise rate is It is linearly related to temperature, so it can be written as: Where a and b are the slope and intercept of the fitting curve respectively; The total energy released by the exothermic chemical reaction during the TR process is expressed as: ΔH TR =m bat c p,bat (T3-T1); Among them, m bat is the mass of the battery, c p,bat is the specific heat capacity of the battery, T3 is the highest temperature of the battery during the TR process, and T1 is the temperature at which the battery loses thermal stability; the heat generation rate of the TR process is expressed as: Among them, c chem represents the dimensionless parameter representing the TR process, is the reaction rate.

7. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 6, characterized in that: When the battery reaches different temperatures, the reaction rates involved in the chemical reaction kinetics equation at the corresponding stages are as follows: 1) When the battery temperature reaches about 90°C, the SEI film of the battery begins to decompose, and the decomposition side reaction will generate heat to continue to increase the battery temperature; therefore, at 90°C, the decomposition reaction of the battery SEI film serves as the basis for triggering the battery thermal runaway; the heat generation rate equation of the SEI film decomposition reaction is: Q SEI =H SEI W SEI R SEI ; The reaction rate involved in the chemical reaction kinetics equation is: Among them, A SEI is the frequency factor of SEI film structure type A; E a,SEI is the activation energy of SEI film structural reaction, kB is the Boltzmann constant; 2) When the battery temperature rises to about 120°C, the negative electrode begins to contact the electrolyte, and the lithium-embedded carbon of the negative electrode reacts with the electrolyte in an exothermic reaction. The heat generation rate equation for the exothermic reaction between the negative electrode and the electrolyte is: Q ne =H ne W ne R ne ; The reaction rate involved in the chemical reaction kinetics equation is: Among them, c ne is the dimensionless quantity of lithium ion content in the negative electrode carbon layer, R ne is the frequency factor of the negative electrode material R type, A ne is the frequency factor of negative electrode material type A, E a,ne is the activation energy of the reaction of the negative electrode material, kB is the Boltzmann constant, t SEI is the time for SEI film structure reaction, m ne C ne The reaction order of 3) When the battery temperature rises to 180°C, the positive electrode active material reacts with the electrolyte to generate heat. This process produces oxygen, accelerates the thermal runaway process of the battery, and releases a large amount of heat. The heat generation rate equation for the exothermic reaction between the positive electrode and the electrolyte is: Q pe =H pe W pe R pe ; The reaction rate involved in the chemical reaction kinetics equation is: Among them, c pe is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode and the positive electrode, R pe is the frequency factor of the positive electrode material R type, A pe is the frequency factor of positive electrode material type A, H pe is the heat generation rate of the positive electrode material reaction, E a,pe is the activation energy of the reaction of the positive electrode material, k is the Boltzmann constant, m pe is the activation energy of α(-); In the early stage of thermal runaway, the gas production inside the battery mainly comes from the decomposition and regeneration of SEI and the evaporation of the electrolyte. The solid electrolyte interface SEI has metastable characteristics and generally decomposes exothermically at 80-120°C. The heat dissipated when the internal mixed gas is exhausted is: Among them, M ele is the molar mass of the electrolyte, H vap is the evaporation enthalpy of the electrolyte, C ele is the gas specific heat of the electrolyte under constant volume conditions, and the molar mass and constant volume specific heat of the gas generated by SEI decomposition and regeneration are expressed as M g and C g , g = SEI d ,SEI r ; 4) When the temperature reaches 200 degrees Celsius, the electrolyte begins to decompose and burn, accelerating the entire thermal runaway process; after the electrolyte decomposes, a large amount of heat is released; the heat generation rate equation of the electrolyte decomposition reaction is: Q e =H e W e R e ; The reaction rate involved in the chemical reaction kinetics equation is: Among them, c e is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode and the positive electrode, R e is the frequency factor of the positive electrode material R type, A e is the frequency factor of positive electrode material type A, W e is the carbon content per unit volume of the positive electrode material, H e is the heat generation rate of the positive electrode material reaction, E a,e is the activation energy of the reaction of the positive electrode material; R is the universal gas constant.

8. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 7, characterized in that: Under normal conditions, the source term ∑Q of the heat conduction equation tot =0; During thermal runaway, ∑Q tot Then it is equal to H i W i R i , i is represented by SEI, ne, pe or ele.

9. The method for constructing a thermal runaway propagation simulation model for a large-capacity energy storage battery according to claim 8, characterized in that: In step S7 shown, the traditional single-battery heat transfer simulation model constructed by step S6 is also applicable to the battery pack heat transfer simulation model. A boundary heat source is set on only one battery to cause thermal runaway, so that the thermal runaway propagates from this battery and induces thermal runaway in other batteries. Probes are added to record the temperature changes of each battery.

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