Energy storage battery thermal runaway expansion simulation method and system of multi-physics field coupling model

Abstract

The invention discloses an energy storage battery thermal runaway expansion simulation method and system of a multi-physics field coupling model. The method comprises the following steps: establishing a coupling model of a lithium ion battery; setting model boundary conditions, and calculating electrochemical heat and reaction heat of the battery cell; calculating the reaction rate in the thermal runaway process of the battery cell, and calculating the gas pressure in the battery; and calculating the expansion deformation of the battery shell and the stress distribution of the shell according to the gas pressure. Mechanical simulation solution is carried out by setting battery model parameters, so that the expansion deformation characteristic and the stress distribution state of the battery shell during thermal runaway of the battery are obtained, and a theoretical basis is provided for a subsequent battery safety monitoring technology.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model. Background Art

[0002] In order to cope with the trend of global climate change and mitigate the impact of global warming, my country has implemented the "carbon peak, carbon neutrality" strategy and simultaneously promoted the construction of new power systems. Lithium battery energy storage technology has a highly flexible adjustment capability and is expected to become a supporting technology to break through the bottleneck of new power system construction. However, safety issues are the key issue for large-scale application of electrochemical energy storage. Lithium batteries are prone to fire or even explosion when used or supervised improperly, causing significant losses.

[0003] During thermal runaway, lithium batteries will experience significant expansion and spontaneous combustion, which will have a significant impact on the safety of energy storage batteries and modules.

[0004] In the work of lithium battery safety monitoring, there are usually two methods to obtain the battery thermal runaway expansion law. One is the experimental method, which obtains the battery expansion state information by conducting destructive tests on lithium batteries. However, this method requires specific experimental equipment and environment, and is dangerous. The other method is to calculate the battery expansion characteristics under thermal runaway conditions through simulation modeling. This method does not require specific equipment and dangerous tests. At present, the simulation technology of lithium battery thermal runaway expansion is still in the exploratory stage. Related work is only focused on cylindrical, soft-pack and small-capacity lithium batteries, and the research level of large-capacity energy storage batteries is relatively low. In addition, since the internal lithium battery is a complex electrical, thermal, gas and solid multi-field coupling environment, it poses great challenges to the convergence and reliability of the model. Unclear mechanism or unreasonable model simplification will lead to poor usability of the simulation model. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for simulating thermal runaway expansion of energy storage batteries using a multi-physics field coupling model, comprising:

[0007] Establish a coupled model of lithium-ion batteries;

[0008] Set the model boundary conditions, calculate the potential change and electrochemical heat generation during the battery charge and discharge cycle according to the set battery size structure, positive and negative electrode and electrolyte active materials, and the side reaction mechanism during battery thermal runaway;

[0009] Analyze the heat transfer process and the temperature distribution of the battery cell based on the electrochemical heat generation data;

[0010] By analyzing the reaction rate during the thermal runaway process of the battery cell, the pressure of the gas generated in the side reaction process on the battery casing is calculated;

[0011] The battery shell expansion deformation and shell stress distribution are calculated based on the gas pressure.

[0012] As a preferred solution of the energy storage battery thermal runaway expansion simulation method of the multi-physical field coupling model described in the present invention, wherein: the coupling model of the lithium-ion battery includes an electrochemical model, a heat transfer model, a side reaction model and a mechanical model, and the battery geometric dimensions, electrochemical parameters, and thermal physical parameters are set;

[0013] When modeling the shell structure of the battery cell, it is set according to the size and structure parameters of lithium-ion batteries with a capacity of 280Ah and above; and the battery cell shell parameters are defined, including the shell length, width and height, the shell elastic modulus E, and the shell material Poisson's ratio μ.

[0014] As a preferred solution of the energy storage battery thermal runaway expansion simulation method of the multi-physics field coupling model described in the present invention, wherein: the battery geometric dimensions include one or more of the width, height, thickness of the positive and negative battery pole pieces, the width, height, thickness and position of the current collector, the width, height and coating thickness of the positive and negative electrode materials, and the number of pole pieces;

[0015] The electrochemical parameters include one or more of reaction rate, solid phase lithium ion concentration, solid phase lithium ion diffusion coefficient, active material volume fraction, particle radius, and boundary current density;

[0016] The battery thermal physical property parameters include one or more of the density, specific heat capacity, and thermal conductivity of each component material of the battery.

[0017] As a preferred solution of the method for simulating thermal runaway expansion of energy storage batteries of the multi-physics field coupling model of the present invention, the coupling model of the lithium-ion battery also includes, based on the lithium-ion battery P2D model, taking into account the diffusion of lithium ions in the positive and negative electrode materials, electronic conduction and the electrochemical reaction on the electrode surface, describing the active materials inside the lithium battery at the particle level, establishing the electrochemical model of the battery cell, being able to accurately simulate the charging and discharging process of the lithium-ion battery, and calculating the battery potential level and electrochemical heat;

[0018] Through solid heat transfer, the physical parameters of thermal conductivity, density and specific heat of the material as well as the heat transfer mechanism of gas passing through the solid surface are considered to describe the heat transfer process on the battery surface and inside, and establish a heat transfer model;

[0019] The energy conservation equation for solid heat transfer of lithium batteries is constructed as follows:

[0020]

[0021] Where ρ is the density; Cp is the specific heat capacity; T is the system temperature; t is the time; is the rate of change of temperature over time; u is the fluid velocity vector; is the temperature gradient vector; is the heat flux divergence; Q is the volume heat source term; k is the thermal conductivity;

[0022] According to the basic theory of series-parallel thermal resistance, the thermal conductivity of the battery body in the x and z directions and the thermal conductivity in the y direction are calculated as follows:

[0023]

[0024] in, is the thermal conductivity of the battery body in the x and z directions; is the thermal conductivity of the battery body in the y direction; L batt is the total thickness of the battery model, L pos , L neg , With L sep Total; kT pos and L pos kT are the thermal conductivity and thickness of the positive electrode active material of the battery respectively; neg and L neg are the thermal conductivity and thickness of the negative electrode active material of the battery respectively; and are the thermal conductivity and thickness of the battery positive electrode collector respectively; and are the thermal conductivity and thickness of the negative electrode current collector of the battery; kT sep and L sep are the thermal conductivity and thickness of the battery positive electrode collector respectively;

[0025] Through the reaction equation interface, based on the reaction mechanism inside the lithium battery during thermal runaway, an ordinary differential equation is established, and the substance content and heat generation are calculated based on the conservation of matter and energy, and a side reaction model is established;

[0026] According to the gas production obtained by the side reaction model, the internal gas pressure of the battery is calculated based on the ideal gas state equation, and the pressure of the internal gas pressure of the battery on the outer wall of the battery shell is calculated, and finally a solid mechanics model representing the deformation of the battery shell and the stress distribution of the shell is obtained.

[0027] As a preferred solution of the energy storage battery thermal runaway expansion simulation method of the multi-physics field coupling model described in the present invention, wherein: the model boundary conditions include the initial charge state of the lithium-ion battery, the battery charge and discharge cut-off voltage, the battery charge and discharge rate, the battery charge and discharge working cycle, the initial ambient temperature, the initial temperature of the battery body, the surface heat convection exchange coefficient, the amount of initial substances of each component in the reaction equation, and the mechanical deformation fixed constraint;

[0028] The total heat source Q in the thermal runaway process of lithium batteries includes electrochemical heat Q1 and side reaction heat Q2. The main source of electrochemical heat is Joule heat during the charging and discharging process of lithium-ion batteries. The Joule heat solution is:

[0029] Q1=I 2 R / V batt

[0030] Among them, Q1 is the electrochemical heat source, i.e. Joule heat; I is the battery current; R is the equivalent internal resistance of the battery; V batt is the battery volume;

[0031] The side reaction heat source Q2 is mainly the heat released by the internal material components reacting and decomposing when the battery has thermal runaway; the sum of the heat sources of all active material decomposition reactions is defined as Q tot , the calculation formula is as follows:

[0032] Q tot =∑H i W i R i

[0033] Among them, H i is the decomposition reaction enthalpy; W i is the unit volume mass content of each active material in the battery; R i The reaction rate of each decomposition reaction; i is each side reaction, including sei, ne, pe and e;

[0034] The side reaction equations are:

[0035]

[0036] Among them, R SEI is the reaction parameter for SEI film decomposition; c SEI is the dimensionless quantity of SEI film; A SEI is the frequency factor of SEI film decomposition; E a,SEI is the activation energy of SEI film decomposition reaction; R ne is the reaction parameter of the negative electrode active material and the electrolyte; c ne A is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode material; ne is the frequency factor of the reaction between the negative electrode active material and the electrolyte; Ea,ne is the activation energy of the reaction between the negative electrode active material and the electrolyte; R pe is the reaction parameter of the positive electrode active material and the electrolyte; c pe A is the dimensionless amount of the positive electrode active material; pe E is the frequency factor of the reaction between the positive electrode active material and the electrolyte; a,pe is the activation energy of the reaction between the positive electrode active material and the electrolyte; R e is the reaction parameter of electrolyte decomposition; c e A is the dimensionless quantity of electrolyte concentration in the electrolyte; e is the frequency factor of electrolyte decomposition; E a,e is the activation energy of electrolyte decomposition; R is the molar gas constant; T is the system temperature.

[0037] As a preferred solution of the energy storage battery thermal runaway expansion simulation method of the multi-physics field coupling model described in the present invention, wherein: the calculation of the gas pressure inside the battery includes, based on the ideal gas state equation, calculating the battery internal boundary gas pressure P through the side reaction equation and the thermal coupling interface;

[0038] P=cRT

[0039]

[0040] Where P is the boundary gas pressure; R is the molar gas constant, is the rate of change of gas concentration over time; r gas is the reaction rate of decomposition and gas production; the temperature T is solved by the heat transfer interface, and the gas concentration c and r gas Solved by the Side Reaction Equation interface, the boundary gas pressure P can be obtained by substituting the concentration c and temperature T.

[0041] As a preferred solution of the energy storage battery thermal runaway expansion simulation method of the multi-physics field coupling model of the present invention, wherein: the calculation of the battery shell expansion deformation and the shell stress distribution according to the internal gas pressure of the battery includes: assuming that the internal gas pressure of the shell is equal everywhere, the load model of the gas on the battery shell can be simplified to the pressure effect of the inner wall of the battery shell with a magnitude of P;

[0042] The battery shell material is set to aluminum alloy, with an elastic modulus of 70 GPa, a Poisson's ratio of 0.39, a yield strength of 140 MPa, and its deformation type is plastic deformation;

[0043] Set the top tab of the lithium battery as a fixed constraint;

[0044] After the physical field is set, calculations are performed to obtain the expansion deformation of the battery shell and the stress distribution of the shell during the battery thermal runaway process.

[0045] A thermal runaway expansion simulation system for an energy storage battery using a multi-physics field coupling model according to the method of the present invention is characterized in that it includes an electrochemical interface, a heat transfer interface, a reaction equation interface, and a solid mechanics interface, wherein:

[0046] Electrochemical interface, used to establish the electrochemical model of lithium-ion batteries. According to the set battery size structure, positive and negative electrodes and electrolyte active materials, it calculates the potential change and electrochemical heat generation during the battery charge and discharge cycle, and feeds the results back to other interfaces;

[0047] Heat transfer interface, used to establish the overall heat transfer model of the battery and the environment, receive heat generation data from the electrochemical and reaction interfaces, and analyze the heat transfer process and the temperature distribution of the battery cell;

[0048] Reaction equation interface, used to reflect the side reaction mechanism during battery thermal runaway, and calculate heat generation and material generation through conservation of matter and energy;

[0049] The Solid Mechanics interface is used to calculate the pressure of the gas generated by the side reaction on the battery shell, thereby calculating the expansion deformation data of the battery shell and the stress distribution of the shell.

[0050] A computer device comprises: a memory and a processor; the memory stores a computer program, wherein: the processor implements the steps of any one of the methods of the present invention when executing the computer program.

[0051] A computer-readable storage medium stores a computer program, wherein: when the computer program is executed by a processor, the steps of any one of the methods of the present invention are implemented.

[0052] Beneficial effects of the present invention: The multi-physics field coupling model provided by the present invention provides a simulation method for thermal runaway expansion of energy storage batteries. By combining the size parameters, electrochemical parameters, thermophysical parameters and side reaction kinetic parameters of energy storage lithium batteries, the electrochemical model, heat transfer model, side reaction model and solid mechanics model of lithium batteries are established through finite element simulation, and the whole process of internal electrothermal coupling, reaction heat release, reaction gas production and battery shell expansion when thermal runaway occurs in lithium batteries is summarized. The present invention proposes a new method for studying thermal runaway expansion of lithium batteries, which can be used to predict the external characteristics of thermal runaway of lithium batteries, and the model can be generalized to various types of lithium battery expansion problems by changing the battery structure and parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0054] Figure 1 An overall flow chart of a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in a second embodiment of the present invention;

[0055] Figure 2 A schematic diagram of a one-dimensional lithium battery electrochemical model in a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in a third embodiment of the present invention;

[0056] Figure 3 A schematic diagram of the coupling relationship between various models in a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in a third embodiment of the present invention;

[0057] Figure 4 A three-dimensional battery model established in a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in a third embodiment of the present invention;

[0058] Figure 5 The voltage variation of a battery model during a charge and discharge cycle in a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in a third embodiment of the present invention;

[0059] Figure 6 The amount change of substances during the thermal runaway reaction in a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in the third embodiment of the present invention;

[0060] Figure 7 The expansion displacement variation process of each point on the battery surface in a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model provided in the third embodiment of the present invention;

[0061] Figure 8 A battery shell expansion deformation cloud map and a battery shell surface stress distribution cloud map in a multi-physics field coupling model thermal runaway expansion simulation method for an energy storage battery provided in the third embodiment of the present invention, wherein the upper row is a battery shell expansion deformation cloud map, and the lower row is a battery shell surface stress distribution cloud map. DETAILED DESCRIPTION

[0062] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0063] Embodiment 1 provides a thermal runaway expansion model for a large-capacity energy storage battery. The model establishment includes the following steps:

[0064] S1: Finite element modeling of single cell expansion. Including: cell shell structure modeling, battery shell size material definition.

[0065] Furthermore, the cell shell structure modeling refers to the size and structure parameters of energy storage batteries with a capacity of 280Ah and above, and defines the cell shell parameters, including the length, width and height of the shell, the shell elastic modulus E, and the Poisson's ratio μ of the shell material.

[0066] S2: Establishment of cell electrochemical model, thermal model, side reaction model and solid mechanics model.

[0067] Furthermore, the cell electrochemical model is established based on the P2D model of lithium batteries. The P2D model describes the active materials inside lithium batteries at the particle level, taking into account the diffusion of lithium ions in the positive and negative electrode materials, electronic conduction, and electrochemical reactions on the electrode surface.

[0068] Thermal modeling is achieved through solid heat transfer, taking into account the physical properties of the material such as thermal conductivity, density and specific heat, as well as the heat transfer mechanism of gas through the solid surface, to describe the heat transfer process on the battery surface and inside.

[0069] The side reaction model is implemented through the reaction equation interface. It reflects a series of reactions inside the lithium battery during thermal runaway. Based on a series of reaction mechanisms inside the lithium battery during thermal runaway, an ordinary differential equation is established, and the material content and heat generation are calculated based on the conservation of matter and energy.

[0070] Among them, the side reactions in the thermal runaway process of lithium batteries include: decomposition of SEI film, reaction of negative electrode active materials with electrolyte, reaction of positive electrode active materials with electrolyte, and decomposition of electrolyte.

[0071] The solid mechanics model is implemented through the solid mechanics interface. The internal gas pressure is calculated by the gas production obtained by the side reaction model and the ideal gas state equation, and then the pressure effect of the internal pressure on the outer wall of the shell is calculated, finally obtaining the battery shell deformation and shell stress distribution.

[0072] S3: Interface and parameter definitions for each part of the electrochemical, thermal, reaction, and solid mechanics models.

[0073] Electrochemical parameters include: positive and negative current collectors, positive and negative electrodes, width, height and thickness of the separator, as well as materials, electrolyte concentration, electrode reaction rate, initial charge of the battery, charge and discharge current, charge and discharge cut-off voltage, etc.; thermal modeling parameters include: thermal conductivity, thermal diffusion coefficient, specific heat capacity, initial ambient temperature, heat flux, etc.; side reaction model parameters include material reaction rate, amount of reactant, reaction enthalpy, etc.; solid mechanics parameters include battery geometry, shell thickness, internal gas boundary pressure, etc.

[0074] S4: Battery cell expansion simulation modeling is completed.

[0075] On the other hand, the battery thermal runaway expansion model based on the first aspect includes an electrochemical interface, a heat transfer interface, a reaction equation interface, and a solid mechanics interface, wherein:

[0076] The electrochemical interface is used to establish an electrochemical model for lithium-ion batteries. According to the set battery size structure, positive and negative electrodes, and electrolyte active materials, it calculates the potential change and electrochemical heat generation during the battery charge and discharge cycle, and feeds the results back to other interfaces.

[0077] The heat transfer interface is used to establish the overall heat transfer model of the battery and the environment, receive the heat generation data of the electrochemical and reaction interfaces, and analyze the heat transfer process and the temperature distribution of the battery cell.

[0078] The reaction equation interface is used to reflect the side reaction mechanism during battery thermal runaway. It calculates heat generation and material generation through conservation of matter and conservation of energy. Material generation here mainly refers to gas generation from electrolyte decomposition. This reaction is the main cause of battery expansion.

[0079] The Solid Mechanics interface is used to calculate the pressure of the gas generated by the side reaction on the battery shell, thereby calculating the expansion deformation data of the battery shell and the stress distribution of the shell.

[0080] Example 2, reference Figure 1 , as an embodiment of the present invention, provides a method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model, comprising:

[0081] Step 1: Establish a coupled model of lithium-ion batteries, including electrochemical, heat transfer, reaction and mechanical models, and determine the battery geometry, electrochemical parameters and thermophysical parameters.

[0082] Specifically, the present invention establishes a three-dimensional battery model according to the specifications and dimensions of a real lithium battery. The real battery reference objects include energy storage battery cells of different capacities such as 280Ah to 320Ah, lithium iron phosphate, ternary lithium, and different materials and sizes.

[0083] Specifically, the geometric parameters of the electrochemical model include one or more of the width, height, and thickness of the positive and negative battery pole pieces, the width, height, and thickness of the current collector and their positions, the width and height of the positive and negative electrode materials, the coating thickness, and the number of pole pieces. The electrochemical parameters include one or more of the reaction rate, the solid phase lithium ion concentration, the solid phase lithium ion diffusion coefficient, the volume fraction of the active material, the particle radius, and the boundary current density. The battery thermal physical parameters include one or more of the density of the battery component materials, the specific heat capacity, and the thermal conductivity.

[0084] The battery electrochemical model is based on the P2D model of Newman et al. The electrochemical model in the present invention is constructed according to the solid phase material conservation equation, liquid phase material conservation equation, solid phase charge conservation equation, liquid phase charge conservation equation and electrochemical kinetic equation of the P2D model. The electrochemical model simplifies the actual battery model to a certain extent, and describes a hierarchical battery structure including a negative electrode collector, a negative electrode porous electrode, a diaphragm, a positive electrode porous electrode, and a positive electrode collector. Lithium-ion batteries are divided into three regions: positive electrode, negative electrode, and diaphragm, and two phases: solid phase (positive and negative electrode active particles) and liquid phase (electrolyte). The current enters and exits the battery through the positive and negative current collectors, and forms a complete working circuit with the external circuit. The electrochemical model can accurately simulate the charging and discharging process of lithium-ion batteries, and calculate the battery potential level and electrochemical heat.

[0085] The heat transfer model of the present invention takes into account the heat transfer process of each material component inside the battery, and the solid heat transfer energy conservation equation of the lithium battery is constructed as follows:

[0086]

[0087] Where ρ is the density; C p is the specific heat capacity; T is the system temperature; t is the time; is the rate of change of temperature over time; u is the fluid velocity vector; is the temperature gradient vector; is the heat flux divergence; Q is the volume heat source term; k is the thermal conductivity.

[0088] In addition, since the battery is made up of multiple electrodes stacked in an interlaced manner, its heat conduction is anisotropic. According to the basic theory of series-parallel thermal resistance, the thermal conductivity of the battery body in the x and z directions and the thermal conductivity in the y direction are calculated as follows:

[0089]

[0090] in, is the thermal conductivity of the battery model surface in the x and z directions; is the thermal conductivity of the battery model in the y direction; L batt is the total thickness of the battery model, L pos , L neg , With Lsep Total; kT pos and L pos kT are the thermal conductivity and thickness of the positive electrode active material of the battery respectively; neg and L neg are the thermal conductivity and thickness of the negative electrode active material of the battery respectively; and are the thermal conductivity and thickness of the battery positive electrode collector respectively; and are the thermal conductivity and thickness of the negative electrode current collector of the battery; kT sep and L sep are the thermal conductivity and thickness of the battery positive electrode collector respectively.

[0091] Step 2: Set the model boundary conditions and calculate the electrochemical heat and reaction heat of the battery cell.

[0092] Specifically, the model boundary conditions include the initial charge state of the lithium-ion battery, the battery charge and discharge cut-off voltage, the battery charge and discharge rate, the battery charge and discharge working cycle, the initial ambient temperature, the initial temperature of the battery body, the surface heat convection exchange coefficient, the initial amount of substance of each component in the reaction equation, the mechanical deformation fixed constraint and other combinations of conditions.

[0093] Specifically, the heat generated by the battery cell includes electrochemical heat and reaction heat, of which the former is the ohmic heat caused by the ohmic internal resistance during the battery charging and discharging process, and the latter is the reaction heat generated by the material reaction during the thermal runaway process. On the other hand, the internal heat of the battery further promotes the side reactions, so the battery thermal model and the reaction equation are bidirectionally coupled. The total heat source Q in the thermal runaway process of the lithium battery is mainly electrochemical heat Q1 and side reaction heat Q2, of which the main source of electrochemical heat is Joule heat during the charging and discharging process of the lithium-ion battery, and Joule heat can be solved according to the following formula:

[0094] Q1=I 2 R / V batt

[0095] Where Q1 is the Joule heat generation rate, W / m3; I is the battery current, A; R is the equivalent internal resistance of the battery, Ω; Vbatt is the battery volume, m3. Joule heat includes the sum of the Joule heat generated by the current of the positive and negative poles of the battery and the Joule heat generated by the electrochemical reaction between the poles inside the battery.

[0096] The side reaction heat Q2 is mainly the heat released by the internal material components reacting and decomposing when the battery has thermal runaway. The side reactions inside the battery during the thermal runaway of the lithium-ion battery under induced conditions mainly include: SEI film decomposition, reaction between the negative electrode and the electrolyte, reaction between the positive electrode and the electrolyte, and decomposition of the electrolyte.

[0097] It should be explained in detail that, based on the research and analysis of thermal runaway tests of lithium-ion monomers, when a lithium-ion battery triggers thermal runaway, a series of chemical exothermic decomposition reactions will occur, and the heat generated by the chemical reactions can be described by chemical reaction kinetics. The ARC test has proved that the chemical reaction kinetics process approximately satisfies the superposition principle, that is, different reactions can be added together. The overall reaction heat of the battery is roughly equal to the superposition of the reaction heats of its components. Therefore, a thermal runaway model of lithium-ion batteries under thermal abuse conditions is constructed based on the Arrhenius formula in chemical reaction kinetics. According to the reference model in the literature, four reactions are considered: SEI decomposition, reaction of negative electrode active materials with electrolyte, reaction of positive electrode active materials with electrolyte, and decomposition reaction of electrolyte. The sum of the heat sources of all active material decomposition reactions is defined as Q tot , the calculation formula is as follows:

[0098] Q tot =∑H i W i R i

[0099] Among them, H i is the decomposition reaction enthalpy, J·kg -1 ; W i is the mass content per unit volume of each active material in the battery, kg·m -3 ; R i The reaction rate of each decomposition reaction, S -1 . In the case of thermal abuse, when the battery temperature reaches about 130°C, the SEI film begins to decompose. The decomposition reaction generates heat and raises the battery temperature. Therefore, this temperature is used as a basis for judging whether the battery will trigger thermal runaway. As the reaction proceeds, when the temperature reaches about 190°C, the SEI film is almost completely decomposed, so it cannot block the contact between the negative electrode and the electrolyte, resulting in an exothermic reaction between the lithium-embedded carbon in the negative electrode and the electrolyte. When the high temperature causes the diaphragm to dissolve, the open circuit voltage of the battery decreases, which can be used as a condition for judging the thermal runaway of lithium-ion batteries. In addition, the reaction between the negative electrode and the electrolyte will produce a new SEI film, which in turn inhibits the reaction. However, due to the small amount of newly generated SEI film and its uneven distribution, it will not completely block the reaction between the negative electrode and the electrolyte, and the new SEI film will continue to decompose. When the temperature exceeds 230°C, the positive electrode active material begins to decompose and react with the electrolyte. Oxygen will be released during the reaction, thereby accelerating the thermal runaway process of the battery. At the same time, the above chemical reactions will also generate a lot of heat; the decomposition reaction of the electrolyte accelerates the entire thermal runaway process. After the electrolyte decomposes, it releases a lot of heat, causing the battery temperature to rise rapidly. At the same time, the combustible gas released in the reaction may burn, causing the battery to explode. The reaction equations of the above side reactions are:

[0100]

[0101] Among them, R SEI is the reaction parameter for SEI film decomposition; c SEI is the dimensionless quantity of SEI film; A SEI is the frequency factor of SEI film decomposition; E a,SEI is the activation energy of SEI film decomposition reaction; R ne is the reaction parameter of the negative electrode active material and the electrolyte; c ne A is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode material; ne is the frequency factor of the reaction between the negative electrode active material and the electrolyte; E a,ne is the activation energy of the reaction between the negative electrode active material and the electrolyte; R pe is the reaction parameter of the positive electrode active material and the electrolyte; c pe A is the dimensionless amount of the positive electrode active material; pe E is the frequency factor of the reaction between the positive electrode active material and the electrolyte; a,ne is the activation energy of the reaction between the positive electrode active material and the electrolyte; R e is the reaction parameter of electrolyte decomposition; c e A is the dimensionless quantity of electrolyte concentration in the electrolyte; e is the frequency factor of electrolyte decomposition; E a,e is the activation energy of electrolyte decomposition; R is the molar gas constant; T is the temperature.

[0102] Step 3, calculate the reaction rate during thermal runaway of the battery cell and calculate the gas pressure inside the battery.

[0103] The present invention is based on the ideal gas state equation and calculates the internal boundary gas pressure P of the battery through the step 2 reaction equation and the thermal coupling interface, where R is the gas constant, the temperature T is solved by the heat transfer interface, and the gas concentration c is solved by the reaction equation interface. Substituting the concentration c and the temperature T into the equation, the internal gas pressure P can be obtained.

[0104] Step 4: Calculate the battery shell expansion deformation and shell stress distribution according to the gas pressure.

[0105] Based on the ideal gas state equation, the gas pressure P at the battery internal boundary is calculated through the side reaction equation and the thermal coupling interface;

[0106] P=cRT

[0107]

[0108] Where P is the boundary gas pressure; R is the gas constant, is the rate of change of gas concentration over time; r gas is the reaction rate of decomposition and gas production; the temperature T is solved by the heat transfer interface, and the gas concentration c and rgas Solving the reaction equation interface, substituting the concentration c and temperature T into the internal gas pressure P can be obtained.

[0109] In order to simplify the complexity of the model and improve the convergence of the simulation calculation, the present invention assumes that the gas pressure inside the shell is equal everywhere, so the load model of the gas on the battery shell can be simplified to the pressure effect on the inner wall of the battery shell of size P. In order to reduce weight, existing energy storage batteries often use aluminum alloy to make battery shells. Therefore, in this application, the battery shell material is set to aluminum alloy with an elastic modulus of 70GPa, a Poisson's ratio of 0.39, a yield strength of 140MPa, and its deformation type is plastic deformation. In addition, when the actual battery is installed, the pole ear is generally welded inside the module, usually welded and fixed on the module bus. Therefore, the top pole ear of the lithium battery is set as a fixed constraint to ensure the computational convergence of the mechanical interface. After the physical field is set, calculations can be performed to obtain the surface expansion displacement and stress distribution during the thermal runaway of the battery.

[0110] The steps for calculating the expansion displacement of the battery surface are as follows: (1) Calculate the reaction heat, reaction rate, and gas pressure inside the battery; (2) Set the material properties of the battery shell size and use the calculated internal gas pressure as the internal load on the battery during expansion; (3) Set the battery tabs as fixed constraints and calculate the battery shell mechanical information through the Comsol solid mechanics interface (fixed constraints refer to the parts that do not deform during the calculation process. Solid mechanics must set fixed constraints to correctly calculate convergence. During use, the tabs of the battery are welded to the battery module bus and fixed, so they meet the conditions for setting as fixed constraints); (4) Obtain the required deformation, stress values, and images through post-processing.

[0111] On the other hand, a multi-physics field coupling model for thermal runaway expansion simulation of energy storage batteries is provided, which is characterized by comprising an electrochemical interface, a heat transfer interface, a reaction equation interface and a solid mechanics interface, wherein:

[0112] The electrochemical interface is used to establish an electrochemical model for lithium-ion batteries. According to the set battery size structure, positive and negative electrodes, and electrolyte active materials, it calculates the potential change and electrochemical heat generation during the battery charge and discharge cycle, and feeds the results back to other interfaces.

[0113] The heat transfer interface is used to establish the overall heat transfer model of the battery and the environment, receive the heat generation data of the electrochemical and reaction interfaces, and analyze the heat transfer process and the temperature distribution of the battery cell.

[0114] The reaction equation interface is used to reflect the side reaction mechanism during battery thermal runaway and calculate heat generation and material generation through conservation of matter and energy.

[0115] The Solid Mechanics interface is used to calculate the pressure of the gas generated by the side reaction on the battery shell, thereby calculating the expansion deformation data of the battery shell and the stress distribution of the shell.

[0116] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, and other media that can store program codes.

[0117] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0118] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0119] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0120] Example 2, reference Figure 2-5 , which is an embodiment of the present invention, provides a simulation method for thermal runaway expansion of energy storage batteries based on a multi-physics field coupling model. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0121] This embodiment takes a large-capacity 280Ah lithium iron phosphate battery as an example, establishes an expansion simulation model of a sample lithium-ion battery, and simulates and calculates the thermal runaway expansion characteristics of the battery.

[0122] Step 1, setting model parameters;

[0123] The model size parameters, electrochemical parameters, thermophysical parameters and side reaction kinetic parameters are shown in Table 1, Table 2, Table 3 and Table 4, respectively.

[0124] Table 1

[0125] parameter value Rated capacity 280Ah Rated voltage 3.2V size 71mm*173mm*204mm Aluminum shell thickness 1.0mm

[0126] Table 2

[0127]

[0128]

[0129] Table 3

[0130]

[0131] Table 4

[0132]

[0133] Step 2: Establish an electrochemical model.

[0134] Figure 2The one-dimensional electrochemical model established for the present invention is shown in the figure. The lithium-ion battery is divided into three regions: positive electrode, negative electrode, and separator, and two phases: solid phase (positive and negative active particles) and liquid phase (electrolyte). The current enters and exits the battery through the positive and negative current collectors, and forms a complete working circuit with the external circuit. Among them, the one-dimensional, two-dimensional and three-dimensional models are all manifestations of electrochemical models. The three-dimensional model refers to the complete three-dimensional hierarchical structure of the lithium battery, and can fully analyze the internal electrochemical behavior of the lithium battery. However, the coupling calculation amount of the full three-dimensional model is large and it is not easy to fit; the one-dimensional model simplifies the battery structure, and the model assumes that lithium ions diffuse only along the thickness direction of the battery. Compared with the three-dimensional model, the one-dimensional model has a simple structure and a low calculation amount, and it also has high-precision electrochemical and electrochemical thermal calculation accuracy. This embodiment establishes a one-dimensional electrochemical model and couples the electrochemical heat to the three-dimensional model for calculation.

[0135] Step 3: Establish a thermal model.

[0136] The heat transfer parameters of the battery body are calculated according to the thermophysical property parameters in Table 3, and a three-dimensional thermal model is established.

[0137] Step 4: Establish a side reaction model.

[0138] According to the battery side reaction kinetic parameters in Table 4, four side reaction ordinary differential equations including SEI decomposition, negative electrode reaction, positive electrode reaction and electrolyte decomposition were established. The trigger temperatures of the four reactions are 395K, 450K, 490K and 500K respectively.

[0139] Step 5, establish a solid mechanics model and calculate the battery expansion results.

[0140] The gas pressure inside the battery case has been obtained in steps 2, 3, and 4 above, and the structural parameters of the battery case are known in Table 1. Therefore, this step can calculate the effect of the internal pressure on the deformation of the case based on the solid mechanics interface.

[0141] Step 6: Output the results of each stage of the model.

[0142] The present invention is based on the porous electrode theory and the pseudo two-dimensional (P2D) model to establish the electrochemical model of lithium iron phosphate battery, and then couples the heat transfer and thermal runaway side reaction equations to analyze and study the electrochemical behavior of thermal runaway inside the battery. Finally, the gas production rate and gas pressure during the thermal runaway process are calculated through the reaction equation, and the surface deformation and stress distribution of the battery shell under the action of internal pressure are analyzed, so as to analyze the surface mechanical characteristics of the thermal runaway expansion battery. Figure 3 The coupling relationship between the models, among which the thermal model and the side reaction model are bidirectionally coupled, specifically, the side reaction generates a lot of heat, causing the battery to rise in temperature, and the temperature rise will further promote the degree of the side reaction. Therefore, the mutual coupling between the models improves the accuracy and reliability of the model.

[0143] Figure 4 The three-dimensional model of lithium battery is established for reference 280Ah energy storage battery, and the structural parameters are shown in Table 1.

[0144] Figure 5 The voltage change of the lithium battery during the charge and discharge process at different rates is simulated. The battery full charge time decreases with the increase of the rate at different rates, and it shows different voltage platform characteristics in the charge and discharge stages. This result is consistent with the actual battery charge and discharge behavior.

[0145] Figure 6 This is the rate of each reaction in the process of thermal runaway of the lithium battery obtained by simulation. In the initial stage, only the SEI film decomposes. As the temperature rises, the negative electrode of the battery participates in the reaction. When the temperature rises further, the positive electrode side reaction is also triggered, releasing a large amount of heat to cause the electrolyte to begin to decompose. The slope in the figure is the rate of occurrence of various reactions. When the reaction is complete, all reactions stop and the thermal runaway process ends.

[0146] Figure 7 The figure shows the deformation displacement of each point on the battery surface during thermal runaway. It can be seen from the figure that the deformation displacement of different parts is different. The expansion displacement is the largest at the center of the battery surface. When the internal pressure is 300kPa, the maximum displacement reaches 13.7mm, and the deformation degree of the surrounding areas decreases successively. In addition, the side of the battery also expands significantly, but its expansion displacement is much smaller than that of the center of the battery in terms of numerical value.

[0147] Figure 8 The figure shows the overall expansion displacement and surface stress distribution of the battery. As the internal pressure increases further, the area of ​​the large displacement region on the battery shell surface increases, and the surface stress also increases, indicating that the battery shell expands significantly under the gas pressure generated by the decomposition of the internal electrolyte. In particular, when the internal pressure exceeds 200kPa, the maximum value of the surface stress no longer changes, indicating that the stress of the battery shell has exceeded the yield limit of the shell material and irreversible deformation has occurred.

[0148] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for simulating thermal runaway expansion of energy storage batteries based on a multi-physics field coupling model, characterized in that: include: Establish a coupled model of lithium-ion batteries; Set the model boundary conditions, calculate the potential change and electrochemical heat generation during the battery charge and discharge cycle according to the set battery size structure, positive and negative electrode and electrolyte active materials, and the side reaction mechanism during battery thermal runaway; Analyze the heat transfer process and the temperature distribution of the battery cell based on the electrochemical heat generation data; By analyzing the reaction rate during the thermal runaway process of the battery cell, the pressure of the gas generated in the side reaction process on the battery casing is calculated; The battery shell expansion deformation and shell stress distribution are calculated based on the gas pressure.

2. The method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model as claimed in claim 1, characterized in that: The coupling model of the lithium-ion battery includes an electrochemical model, a heat transfer model, a side reaction model and a mechanical model, and sets the battery geometric dimensions, electrochemical parameters and thermophysical parameters; When modeling the shell structure of the battery cell, it is set according to the size and structure parameters of lithium-ion batteries with a capacity of 280Ah and above; and the battery cell shell parameters are defined, including the shell length, width and height, the shell elastic modulus E, and the shell material Poisson's ratio μ.

3. The method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model as claimed in claim 2, characterized in that: The battery geometric dimensions include the width, height, thickness of the positive and negative battery pole pieces, the width, height, thickness and position of the current collector, the width, height and coating thickness of the positive and negative electrode materials, and the number of pole pieces; The electrochemical parameters include reaction rate, solid phase lithium ion concentration, solid phase lithium ion diffusion coefficient, active material volume fraction, particle radius, and boundary current density; The battery thermal physical parameters include the density, specific heat capacity and thermal conductivity of each component material of the battery.

4. The method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model as claimed in claim 3, characterized in that: The coupling model of the lithium-ion battery also includes, based on the lithium battery P2D model, taking into account the diffusion of lithium ions in the positive and negative electrode materials, electronic conduction and the electrochemical reaction on the electrode surface, describing the active materials inside the lithium battery at the particle level, establishing an electrochemical model, and calculating the battery potential level and electrochemical heat; Through solid heat transfer, the physical parameters of thermal conductivity, density and specific heat of the material as well as the heat transfer mechanism of gas passing through the solid surface are considered to describe the heat transfer process on the battery surface and inside, and establish a heat transfer model; The energy conservation equation for solid heat transfer of lithium batteries is constructed as follows: Where ρ is the density; C p is the specific heat capacity; is the rate of change of temperature over time; u is the fluid velocity vector; is the temperature gradient vector; is the heat flux divergence; Q is the volume heat source term; k is the thermal conductivity; T is the system temperature; t is the time; According to the basic theory of series-parallel thermal resistance, the thermal conductivity of the battery body in the x and z directions and the thermal conductivity in the y direction are calculated as follows: in, is the thermal conductivity of the battery body in the x and z directions; is the thermal conductivity of the battery body in the y direction; L batt is the total thickness of the battery model, L pos , L neg , With L sep Total; kT pos and L pos kT are the thermal conductivity and thickness of the positive electrode active material of the battery respectively; neg and L neg are the thermal conductivity and thickness of the negative electrode active material of the battery respectively; and are the thermal conductivity and thickness of the battery positive electrode collector respectively; and are the thermal conductivity and thickness of the negative electrode current collector of the battery; kT sep and L sep are the thermal conductivity and thickness of the battery positive electrode collector respectively; Through the reaction equation interface, based on the reaction mechanism inside the lithium battery during thermal runaway, an ordinary differential equation is established, and the substance content and heat generation are calculated based on the conservation of matter and energy, and a side reaction model is established; According to the gas production obtained by the side reaction model, the internal gas pressure of the battery is calculated based on the ideal gas state equation, and the pressure of the internal gas pressure of the battery on the outer wall of the battery shell is calculated, and finally a solid mechanics model representing the deformation of the battery shell and the stress distribution of the shell is obtained.

5. The method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model as claimed in claim 4, characterized in that: The model boundary conditions include the initial state of charge of the lithium-ion battery, the battery charge and discharge cut-off voltage, the battery charge and discharge rate, the battery charge and discharge working cycle, the initial ambient temperature, the initial temperature of the battery body, the surface heat convection exchange coefficient, the amount of initial substances of each component in the reaction equation, and the mechanical deformation fixed constraint; The total heat source Q in the thermal runaway process of lithium batteries includes electrochemical heat source Q1 and side reaction heat source Q2. The electrochemical heat source is the Joule heat in the charging and discharging process of lithium-ion batteries. The Joule heat solution is: Q1=I 2 R / V batt Among them, Q1 is the electrochemical heat source, namely Joule heat; I is the battery current; R is the equivalent internal resistance of the battery; V batt is the battery volume; The side reaction heat source Q2 is the heat released by the internal material components reacting and decomposing when the battery thermal runaway occurs; the sum of the heat sources of all active material decomposition reactions is defined as Q tot , the calculation formula is as follows: Q tot =∑H i W i R i Among them, H i is the decomposition reaction enthalpy; W i is the unit volume mass content of each active material in the battery; R i The reaction rate of each decomposition reaction; i is each side reaction, including sei, ne, pe and e; The side reaction equations are: Among them, R SEI is the reaction parameter for SEI film decomposition; c SEI is the dimensionless quantity of SEI film; A SEI is the frequency factor of SEI film decomposition; E a,SEI is the activation energy of SEI film decomposition reaction; R ne is the reaction parameter of the negative electrode active material and the electrolyte; c ne A is the dimensionless quantity of lithium ion content in the carbon layer of the negative electrode material; ne is the frequency factor of the reaction between the negative electrode active material and the electrolyte; E a,ne is the activation energy of the reaction between the negative electrode active material and the electrolyte; R pe is the reaction parameter of the positive electrode active material and the electrolyte; c pe A is the dimensionless amount of the positive electrode active material; pe E is the frequency factor of the reaction between the positive electrode active material and the electrolyte; a,pe is the activation energy of the reaction between the positive electrode active material and the electrolyte; R e is the reaction parameter of electrolyte decomposition; c e A is the dimensionless quantity of electrolyte concentration in the electrolyte; e is the frequency factor of electrolyte decomposition; E a,e is the activation energy of electrolyte decomposition; R is the molar gas constant; T is the system temperature.

6. The method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model as claimed in claim 5, characterized in that: The calculating of the gas pressure inside the battery includes calculating the gas pressure P of the battery internal boundary through the side reaction equation and the thermal coupling interface based on the ideal gas state equation; P=cRT Where P is the boundary gas pressure; is the rate of change of gas concentration over time; r gas is the reaction rate of decomposition and gas production; the temperature T is solved by the heat transfer interface, and the gas concentration c and r gas Solved by the Side Reaction Equation interface, the boundary gas pressure P can be obtained by substituting the concentration c and temperature T.

7. The method for simulating thermal runaway expansion of an energy storage battery using a multi-physics field coupling model as claimed in claim 6, characterized in that: The calculation of the battery shell expansion deformation and the shell stress distribution according to the internal gas pressure of the battery includes: assuming that the internal gas pressure of the shell is equal everywhere, the load model of the gas on the battery shell can be simplified to a pressure effect of magnitude P on the inner wall of the battery shell; The battery shell material is set to aluminum alloy, with an elastic modulus of 70 GPa, a Poisson's ratio of 0.39, a yield strength of 140 MPa, and its deformation type is plastic deformation; Set the top tab of the lithium battery as a fixed constraint; After the physical field is set, calculations are performed to obtain the expansion deformation of the battery shell and the stress distribution of the shell during the battery thermal runaway process.

8. A thermal runaway expansion simulation system for energy storage batteries using a multi-physics field coupling model according to any one of the methods of claims 1 to 7, characterized in that: Includes the Electrochemistry interface, the Heat Transfer interface, the Reaction Equation interface, and the Solid Mechanics interface, including: Electrochemical interface, used to establish the electrochemical model of lithium-ion batteries. According to the set battery size structure, positive and negative electrodes and electrolyte active materials, it calculates the potential change and electrochemical heat generation during the battery charge and discharge cycle, and feeds the results back to other interfaces; Heat transfer interface, used to establish the overall heat transfer model of the battery and the environment, receive heat generation data from the electrochemical and reaction interfaces, and analyze the heat transfer process and the temperature distribution of the battery cell; Reaction equation interface, used to reflect the side reaction mechanism during battery thermal runaway, and calculate heat generation and material generation through conservation of matter and energy; The Solid Mechanics interface is used to calculate the pressure of the gas generated by the side reaction on the battery shell, thereby calculating the expansion deformation data of the battery shell and the stress distribution of the shell.

9. A computer device comprising: A memory and a processor; the memory stores a computer program, wherein the processor implements the steps of any method as claimed in claim 1 when executing the computer program.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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