Method for determining kinetic parameters of electrolyte fire in lithium-ion battery and method for evaluating its fire hazard

Abstract

The present invention provides a method for determining the fire kinetic parameters of a lithium-ion battery electrolyte and a method for evaluating its fire hazard. The method for determining the fire kinetic parameters of a lithium-ion battery electrolyte includes the following steps: S1: Construct an electrolyte group model and obtain electrolyte environment parameters; S2: Obtain the evaporation free energy and the standard reaction Gibbs free energy of each elementary reaction; S3: Construct a combustion elementary reaction model; S4: Construct a chain chemical reaction model for each component of the electrolyte and calculate the reaction Gibbs free energy of each elementary reaction at different temperatures; S5: Determine the fire chemical kinetic parameters. Compared with the traditional experimental method, the present invention is faster and more accurate, can effectively reduce the model construction time, significantly improve the calculation accuracy, obtain more accurate fire kinetic parameters of the electrolyte, and thus accurately and quickly evaluate the fire hazard of lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of combustion and fire numerical simulation, and in particular to a method for determining fire kinetic parameters of lithium-ion battery electrolyte and a method for evaluating its fire hazard. Background Technique

[0002] In recent years, lithium-ion battery fires have occurred frequently, causing serious casualties and economic losses. As an important research technology, combustion and fire numerical simulation technology is an important basis for studying the fire laws of lithium-ion batteries and safety improvement. The thermal decomposition and combustion mechanism model of lithium-ion battery electrolyte and fire kinetic parameters are the key basis for accurate and efficient numerical simulation of lithium-ion battery fires, and can provide a theoretical basis and data basis for studying the fire behavior and gas release law during the lithium-ion battery fire process.

[0003] However, there are significant differences between the chemical composition and combustion properties of lithium-ion battery electrolyte and traditional fuels. The electrolyte is mostly a mixed liquid with complex components and there are many side reactions during the combustion process. Moreover, the research on the combustion and fire mechanism of lithium-ion batteries is still in its infancy, lacking relevant combustion chemical reaction mechanisms and fire kinetic parameters of the electrolyte. Therefore, it is impossible to accurately obtain the fire behavior and gas release law during the lithium-ion battery fire process, and thus impossible to accurately evaluate the fire hazard of lithium-ion batteries. If the traditional experimental methods constructed using existing combustion models are used, the evaluation efficiency will be very low and the accuracy will not be high. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of improving the accuracy of evaluating the fire hazard of lithium-ion batteries, and to provide a method for determining fire kinetic parameters of lithium-ion battery electrolyte and a method for evaluating its fire hazard.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for determining fire kinetic parameters of lithium-ion battery electrolyte, comprising the following steps:

[0007] S1: Construct an electrolyte group model and obtain electrolyte environment parameters;

[0008] S2: Obtain the evaporation free energy and the standard reaction Gibbs free energy of each elementary reaction according to the electrolyte group model and the electrolyte environment parameters;

[0009] S3: Construct a combustion elementary reaction model based on the electrolyte group model;

[0010] S4: Construct a chain chemical reaction model of each component of the electrolyte based on the combustion elementary reaction model, the evaporation free energy and the standard reaction Gibbs free energy of each elementary reaction, and calculate the reaction Gibbs free energy of each elementary reaction at different temperatures;

[0011] S5: Determine the fire kinetics parameters according to the reaction Gibbs free energy of each elementary reaction at different temperatures.

[0012] In some embodiments, step S2 includes:

[0013] S21: Obtain the Gibbs free energy correction factor according to the electrolyte group model and the electrolyte environment parameters, and calculate the standard Gibbs free energy of each group in the two environments of electrolyte and air;

[0014] S22: Obtain the evaporation free energy of the gas group and the standard reaction Gibbs free energy of each elementary reaction based on the standard Gibbs free energy.

[0015] In some embodiments, the construction of the chain chemical reaction model of each component of the electrolyte includes: respectively constructing the chain chemical reaction model of each component of the electrolyte under the electrolyte environment conditions and the air environment conditions, and using the standard reaction Gibbs free energy of each elementary reaction as a measurement standard to judge whether the construction of the chain chemical reaction model of each component of the electrolyte is reasonable.

[0016] In some embodiments, step S5 includes:

[0017] S51: Fit the reaction Gibbs free energy of the elementary reaction at different temperatures to obtain the curve of the activation energy of the elementary reaction at different temperatures changing with temperature;

[0018] S52: Calculate the activation energy and temperature coefficient of each elementary reaction according to the curve of the activation energy of the elementary reaction at different temperatures changing with temperature;

[0019] S53: Obtain the reaction rate constant of the elementary reaction according to the curve of the activation energy of the elementary reaction at different temperatures changing with temperature and the activation energy and temperature coefficient of each elementary reaction;

[0020] S54: Obtain the pre-exponential factor of the elementary reaction according to the activation energy and temperature coefficient of each elementary reaction and the reaction rate constant of the elementary reaction.

[0021] In some embodiments, the reaction rate constant of the elementary reaction is represented by the following formula:

[0022]

[0023] Among them, σ is the reaction path degeneracy, k B is the Boltzmann constant, h is the Planck constant, T is the temperature, ΔG T is the reaction Gibbs free energy of the elementary reaction, and R is the gas constant;

[0024] The pre-exponential factor of the elementary reaction is represented by the following formula:

[0025]

[0026] where k T is the reaction rate constant of the elementary reaction, E0 is the activation energy of the fire kinetics parameter, n is the temperature coefficient, T is the temperature, and R is the gas constant.

[0027] In some embodiments, in step S1, the electrolyte environment parameters include the dielectric constant of the electrolyte solution environment, and the quantum chemical calculation solution solvent model parameters are set according to the dielectric constant of the electrolyte solution environment.

[0028] In some embodiments, in step S5, the reaction Gibbs free energy of each elementary reaction at different temperatures is the Gibbs free energy of the reaction of each elementary reaction at m temperature points from 200K to 1000K, where m≥5.

[0029] In some embodiments, the electrolyte group model in step S1 includes a thermal decomposition and combustion model in an electrolyte environment and a thermal decomposition and combustion model in an air environment.

[0030] The present invention also provides a method for evaluating the fire hazard of a lithium-ion battery, including the following steps:

[0031] A1: Input the combustion elementary reaction model, the chain chemical reaction model of each component of the electrolyte, and the fire kinetics parameters in the above method into a hydrodynamic fire numerical simulation program to obtain the lithium-ion battery fire numerical simulation result;

[0032] A2: Obtain the lithium-ion battery fire hazard evaluation result according to the lithium-ion battery fire numerical simulation result.

[0033] The present invention also provides a computer-readable medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the above method are implemented.

[0034] The present invention has the following beneficial effects:

[0035] Due to the lack of fire dynamics parameters in the field of numerical simulation of lithium-ion battery fires, a large number of experiments are required to evaluate the fire hazard of lithium-ion batteries by numerical simulation of fires. The experimental time and cost are high, and the calculation accuracy is low. Therefore, it is impossible to accurately and quickly determine the fire dynamics parameters of lithium battery electrolytes and evaluate the fire hazard of lithium-ion batteries. However, the present invention can obtain more accurate fire dynamics parameters of the electrolyte by constructing a chain chemical reaction model of each component of the electrolyte. Through the obtained combustion elementary reaction model, the chain chemical reaction model of each component of the electrolyte, and the fire dynamics parameters that can be directly coupled with the computational fluid dynamics fire numerical simulation program, the lack of mechanism parameters in the field of numerical simulation of lithium-ion battery fires is filled. It is easy to use and promote. Compared with the traditional experimental method, the present invention is faster and more accurate, can effectively reduce the model construction time, reduce the experimental cost, and significantly improve the calculation accuracy, so as to accurately and quickly evaluate the fire hazard of lithium-ion batteries.

[0036] Other beneficial effects in the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of a method for determining the fire dynamics parameters of a lithium-ion battery electrolyte in an embodiment of the present invention;

[0038] Figure 2 is a flow chart of a method for constructing a combustion mechanism model of a lithium-ion battery electrolyte and determining fire dynamics parameters in an embodiment of the present invention;

[0039] Figure 3a is a reaction path diagram of the thermal decomposition of DMC molecules in a solution environment in an experimental example of the present invention;

[0040] Figure 3b is a reaction path diagram of the thermal decomposition of DMC molecules in an air environment in an experimental example of the present invention;

[0041] Figure 4a is a schematic diagram of the curve of the Gibbs free energy of the CH3OCOOCH3 group varying with temperature in an experimental example of the present invention;

[0042] Figure 4b is a schematic diagram of the curve of the Gibbs free energy of the CH3OCOOCH2 group varying with temperature in an experimental example of the present invention;

[0043] Figure 4c is a schematic diagram of the curve of the Gibbs free energy of the H group varying with temperature in an experimental example of the present invention;

[0044] Figure 4d is a schematic diagram of the curve of the reaction Gibbs free energy varying with temperature in an experimental example of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0046] As Figure 1 shown, the steps of the method for determining the fire kinetic parameters of the lithium-ion battery electrolyte according to the embodiments of the present invention are as follows, including:

[0047] S1: Construct an electrolyte group model and obtain electrolyte environment parameters;

[0048] S2: Obtain the evaporation free energy and the standard reaction Gibbs free energy of each elementary reaction according to the electrolyte group model and the electrolyte environment parameters;

[0049] S3: Construct a combustion elementary reaction model based on the electrolyte group model;

[0050] S4: Construct the thermal decomposition and oxidation reaction paths of each component of the electrolyte based on the combustion elementary reaction model, the evaporation free energy, and the standard reaction Gibbs free energy of each elementary reaction, and calculate the reaction Gibbs free energy of each elementary reaction at different temperatures;

[0051] S5: Determine the fire kinetic parameters of the elementary reaction according to the reaction Gibbs free energy of each elementary reaction at different temperatures.

[0052] As Figure 2 shown, the construction of the combustion mechanism model of the lithium-ion battery electrolyte and the method for determining the fire kinetic parameters include the following steps:

[0053] Step 1, construct an electrolyte group model and obtain electrolyte environment parameters;

[0054] The construction of the electrolyte group model is as follows:

[0055] According to the components of the lithium-ion battery electrolyte, the quantum chemistry calculation method is used to model the groups that may form chemical bond breakage during the thermal decomposition and oxidation processes of each component molecule of the electrolyte. There are two possible situations in the thermal decomposition combustion process of the electrolyte. The first possible situation is that the electrolyte molecules undergo thermal decomposition in the liquid environment to generate thermal decomposition products. The second possible situation is that the electrolyte molecules first evaporate into the gaseous state and then undergo thermal decomposition and oxidation in the air environment. Therefore, the construction of the thermal decomposition and combustion mechanism model of the battery electrolyte in the embodiments of the present invention can be divided into two parts, namely, the thermal decomposition and combustion model in the electrolyte environment and the thermal decomposition and combustion model in the air environment.

[0056] The calculation of the electrolyte environment parameters is as follows:

[0057] Set the quantum chemical calculation solution solvent model parameters according to the dielectric constant of the electrolyte. The main parameter of the electrolyte model is its dielectric constant. The dielectric constant of the electrolyte is the sum of the dielectric constants of its components multiplied by their respective volume fractions. The calculation formula is as follows:

[0058]

[0059] In the formula, ε is the dielectric constant; is the volume fraction; n is the component serial number.

[0060] Step 2: Determine the optimized structure and Gibbs free energy correction factor of each group, and the specific content is as follows:

[0061] Adopt the quantum chemical calculation method to optimize the structures of the reactants, products and reaction transition state groups that may be generated during the thermal decomposition and oxidation chemical reaction processes under the electrolyte environment conditions and vacuum environment conditions respectively, and obtain the thermodynamic correction factor G of the Gibbs free energy of the group 校正 , (G 校正 is the Gibbs free energy correction factor of the group, unit, J / mol).

[0062] Step 3: Determine the standard Gibbs free energy of each group, and the specific content is as follows:

[0063] Adopt the quantum chemical calculation method to perform high-precision single-point energy calculations on each optimized group under the electrolyte environment conditions and vacuum environment conditions respectively, and obtain its electronic energy E 电子 , (E 电子 is the electronic energy of the group, unit, J / mol); and calculate its standard Gibbs free energy G 0 (G 0 is the standard Gibbs free energy of the group, unit, J / mol), and the calculation formula is as follows:

[0064] G 0 = E 电子 + G 校正

[0065] Step 4: Determine the evaporation free energy of each group, and the specific content is as follows:

[0066] Calculate the evaporation free energy of each gas group respectively, which is used to represent the energy change of the electrolyte molecules from the liquid state to the gaseous state. The calculation formula is as follows:

[0067]

[0068] In the formula, and are the standard evaporation Gibbs free energy of the group, the standard Gibbs free energy of the gaseous molecule of the group and the standard Gibbs free energy of the liquid molecule of the group respectively, unit, J / mol.

[0069] Step 5: Construct a combustion elementary reaction model and calculate its standard reaction Gibbs free energy. The specific content is as follows:

[0070] Construct an elementary reaction model for the possible chemical bond breaking processes in the thermal decomposition and oxidation processes of each component molecule of the electrolyte, and calculate the standard reaction Gibbs free energy ΔG of the elementary reaction 0 , and the calculation formula is as follows:

[0071]

[0072] In the formula, ΔG 0 , and are the standard reaction Gibbs free energy, the standard Gibbs free energy of the group at the end of the reaction, and the standard Gibbs free energy of the group at the beginning of the reaction of the elementary reaction, respectively. The unit is J / mol.

[0073] Step 6: Construct a chain chemical reaction model for each component of the electrolyte. The specific content is as follows:

[0074] Construct a chain chemical reaction model for each component of the electrolyte under the electrolyte environmental conditions and air environmental conditions, respectively, and use the reaction Gibbs free energy as a measure to judge whether the construction of the chain chemical reaction model of each component of the electrolyte is reasonable, and draw a thermal decomposition and combustion reaction path diagram of each component of the electrolyte.

[0075] Step 7: Determine the reaction Gibbs free energy of the elementary reaction at different temperatures. The specific content is as follows:

[0076] According to the thermal decomposition and combustion reaction paths of each component of the electrolyte obtained in Step 6, calculate the Gibbs free energy correction factor of each group at m (m≥5) temperature points from 200K to 1000K, and calculate the Gibbs free energy G of each group at each temperature point T (G T is the Gibbs free energy of the group at temperature T, and T is the thermodynamic temperature, with the unit K), and the calculation formula is as follows,

[0077] G T =E 电子 +G 校正-T

[0078] In the formula, G 校正-T is the Gibbs free energy correction factor of the group, and the unit is J / mol.

[0079] Fit to obtain the curve of G T changing with temperature.

[0080] According to the thermal decomposition and combustion reaction paths of each component of the electrolyte, calculate the Gibbs free energy ΔG of each elementary reaction at a total of m temperature points from 200K to 1000K. T , and obtain the fitted ΔG T variation curve with temperature. The calculation formula is as follows:

[0081]

[0082] In the formula: ΔG T , and are the reaction Gibbs free energy of the elementary reaction, the group Gibbs free energy at the end of the reaction, and the group Gibbs free energy at the beginning of the reaction at temperature T, respectively. The unit is J / mol.

[0083] Step eight, determine the kinetic parameters of the elementary reaction combustion fire, which is implemented in four steps in total. The specific content is as follows:

[0084] The first step, from the variation curve of the reaction activation energy with temperature at different temperatures, according to the Arrhenius equation (Adams three-parameter correction model), as follows:

[0085]

[0086] In the formula, k T is the reaction rate constant at temperature T; A is the pre-exponential factor; E0 is the activation energy of the elementary reaction, with the unit J / mol; n is the temperature coefficient; R is the molar gas constant, R = 8.314, with the unit J / (K·mol).

[0087] Take the logarithm of both sides of the above formula, then differentiate with respect to temperature T, and substitute it into the differential form of the Arrhenius equation to obtain:

[0088] E T = E0 + nRT

[0089] In the formula, E T is the activation energy at temperature T, with the unit J / mol.

[0090] E T = ΔG T

[0091] Plot the curve of the elementary reaction E T versus temperature T and perform linear fitting. The fitting form is:

[0092] E T = aT + b, R 2

[0093] In the formula, a is the slope of the curve; b is the intercept of the curve; R 2 is the curve fitting degree.

[0094] Step 2: Calculation of the activation energy and temperature coefficient of the elementary reaction. According to the fitting curve of the activation energy of the reaction at different temperatures obtained in the first step, the activation energy E0 and temperature coefficient n of the fire kinetic parameters can be calculated. The calculation formulas are as follows:

[0095] E0 = b

[0096]

[0097] Step 3: Calculation of the reaction rate constant of the elementary reaction. According to the reaction Gibbs free energy ΔG of the elementary reaction at temperature T obtained in Step 7, calculate the reaction rate constant k of the elementary reaction at temperature T T , and calculate the reaction rate constant k of the elementary reaction at temperature T T

[0098]

[0099] In the formula, σ is the degeneracy of the reaction path, and σ = 1; k B is the Boltzmann constant, k B = 1.3806503×10 -23 , unit, J / K; h is the Planck constant, h = 6.6260696×10 -34 , unit, J·s, R is the gas constant, R = 8.314, unit J / (mol·K).

[0100] Step 4: Calculation of the pre-exponential factor of the elementary reaction. According to the Arrhenius equation, substitute the activation energy E0, temperature coefficient n and reaction rate constant k at temperature T of the fire kinetic parameters calculated in the second and third steps T to obtain:

[0101]

[0102] In summary, the three kinetic parameters required for the elementary reaction model, namely the activation energy E0, temperature coefficient n and pre-exponential factor A, can be obtained.

[0103] In the embodiment of the present invention, by constructing an elementary reaction model during the thermal decomposition and combustion of the electrolyte, a chain chemical reaction model of each component of the electrolyte is constructed, and the fire kinetic parameters of the thermal decomposition and combustion products and their reactions are obtained, so as to accurately describe the product generation and energy change laws during the thermal decomposition and combustion processes of lithium-ion batteries, and provide a mechanism model for the combustion and fire numerical simulation of lithium-ion batteries.

[0104] After confirming the components of the lithium-ion battery electrolyte to be modeled in the embodiments of the present invention, a group model of its components is constructed, and the electrolyte dielectric environment parameters are calculated; then, using quantum chemical simulation technology, the structures of each group are optimized to obtain their electronic energies and Gibbs free energy correction factors, and the standard Gibbs free energy of each group is calculated; then, the evaporation free energy of each group is calculated; then, the elementary reaction models of the thermal decomposition and oxidation of the electrolyte are constructed, and their standard reaction Gibbs free energies are calculated; then, a chain chemical reaction model of each component of the electrolyte is constructed, and based on this, the reaction Gibbs free energy of the elementary reaction at different temperatures is calculated; finally, the fire kinetics parameters are calculated.

[0105] The method for evaluating the fire hazard of a lithium-ion battery according to the embodiments of the present invention includes the following steps:

[0106] A1: Input the combustion elementary reaction model, the chain chemical reaction model of each component of the electrolyte, and the fire kinetics parameters in the above method into a computational fluid dynamics fire numerical simulation program to obtain the lithium-ion battery fire numerical simulation results;

[0107] A2: Obtain the lithium-ion battery fire hazard assessment result according to the lithium-ion battery fire numerical simulation result.

[0108] Specifically, the combustion elementary reaction model, the chain chemical reaction model of each component of the electrolyte, and the fire kinetics parameters generated in the embodiments of the present invention can be directly imported into programs such as the combustion kinetics analysis software CHMEKIN and the computational fluid dynamics of fire software ANSYS FLUENT in the form of a txt text file, providing the necessary combustion reaction kinetics model and fire kinetics parameters for the fire numerical simulation work of the program, obtaining the lithium-ion battery fire numerical simulation results, greatly improving the accuracy, efficiency, and accuracy of the fire numerical simulation, and thus being able to accurately and quickly evaluate the fire hazard of the lithium-ion battery. The present invention fills the gap in the lack of mechanism parameters in the field of lithium-ion battery fire numerical simulation, and is easy to use and promote. Compared with the traditional experimental methods for constructing existing combustion models, the present invention is more rapid and accurate, can effectively reduce the model construction time, reduce the experimental cost, and significantly improve the calculation accuracy.

[0109] The combustion mechanism model and fire kinetics parameters obtained in the embodiments of the present invention can be directly coupled with the computational fluid dynamics fire numerical simulation program, filling the gap in the lack of mechanism parameters in the field of lithium-ion battery fire numerical simulation, and being easy to use and promote. Compared with the traditional experimental methods for constructing existing combustion models, the embodiments of the present invention are more rapid and accurate, can effectively reduce the model construction time, reduce the experimental cost, and significantly improve the calculation accuracy, so as to accurately and quickly evaluate the fire hazard of the lithium-ion battery.

[0110] An embodiment of the present invention also provides a computer-readable medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the above method are implemented.

[0111] Experimental Example

[0112] Next, the technical solutions in the experimental examples of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0113] Taking the component of dimethyl carbonate (DMC) in commercial electrolytes as an example, the implementation method of the experimental example of the present invention will be described in detail, and the specific content is as follows:

[0114] Lithium-ion battery electrolytes are usually substances composed of a mixture of multiple components. During the combustion process of lithium-ion batteries, their thermal decomposition and oxidation reactions and the number of products are extremely numerous and extremely complex, with many side reactions and products. Existing experimental means and methods are difficult to measure the combustion products, by-products, transition states, and their reaction rates and energy changes during the combustion process of electrolytes. Therefore, quantum chemical calculation methods can be used to construct the thermal decomposition and oxidation elementary reactions of each component in the electrolyte during the combustion process, and determine their fire kinetic parameters, and finally obtain the combustion kinetic mechanism model of lithium-ion batteries, so as to accurately and quickly evaluate the fire hazard of lithium-ion batteries.

[0115] In this embodiment, a common commercial electrolyte is taken as an example, which is composed of a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). Its components are shown in Table 1 below:

[0116] Table 1

[0117]

[0118] According to the method described in the experimental example of the present invention, a thermal decomposition model of the DMC component in this commercial electrolyte combustion model is constructed, and the specific implementation method is as follows:

[0119] Step 1: Construct the reactant and product groups in the thermal decomposition reaction process according to the above electrolyte components. Model the DMC molecule (CH3OCOOCH3), and model the groups that may be generated during the thermal decomposition of the DMC molecule in two environments: in solution and in air. These include: groups such as CH3OCOOCH3, CH3OCOOCH2-, H-, CH3OCOO-, CH3-, CH3OCO-, CH3O-, -CH2O-, CO2.

[0120] Calculation of electrolyte environmental parameters: According to the above electrolyte components, calculate the dielectric constant of this electrolyte solution environment. The electrolyte solution model is mainly its dielectric constant. The dielectric constant of the electrolyte is the sum of the dielectric constants of its respective components multiplied by their respective volume fractions. The calculation method is as follows:

[0121]

[0122] Step 2: Optimize the structures of the groups generated during the DMC thermal decomposition process constructed in Step 1 and calculate their Gibbs free energy correction factors. Using quantum chemical calculation methods, select the B3LYP (a density functional) / 6-31G+(d) basis set, and optimize the structures of the groups generated during the DMC thermal decomposition process under electrolyte environmental conditions (the electrolyte environment is simulated using the implicit solvent (SMD) model, (ε = 31.90)) and air environmental conditions (ε = 0) respectively, and obtain the Gibbs free energy correction factors of the groups in the solution environment and air environment from the optimization results. and

[0123] Step 3: Calculate the Gibbs free energy of the groups generated during the DMC thermal decomposition process whose structures have been optimized in Step 2. Using quantum chemical calculation methods, adopt the M05-2X (a density functional) / 6-31G(d) basis set combined with the SMD model (ε = 31.90) to calculate the electronic energy of the groups generated during the DMC thermal decomposition process under electrolyte environmental conditions. Perform the calculation; adopt the M05-2X / 6-31G(d) basis set to calculate the electronic energy of the groups generated during the DMC thermal decomposition process under air environmental conditions. Perform the calculation. Combining the Gibbs free energy correction factors of the groups generated during the DMC thermal decomposition process obtained in Step 2, calculate the standard Gibbs free energy of each group. Taking the DMC molecule as an example, the calculation method is as follows:

[0124]

[0125]

[0126] In the formula: represents the standard Gibbs free energy of the DMC molecule in the solution environment, unit: J / mol; represents the electronic energy of the DMC molecule in the solution environment, unit: J / mol; represents the standard Gibbs free energy correction factor of the DMC molecule in the solution environment, unit: J / mol; represents the standard Gibbs free energy of the DMC molecule in the air environment, unit: J / mol; represents the electronic energy of the DMC molecule in the air environment, unit: J / mol; represents the standard Gibbs free energy correction factor of the DMC molecule in the air environment, unit: J / mol.

[0127] Step 4: Calculate the evaporation free energy of each group generated during the thermal decomposition of DMC. The evaporation free energy is used to represent the change in free energy during the transformation of molecules from liquid to gas in the solution during the thermal decomposition of DMC. The molecules that can evaporate during the thermal decomposition of DMC are DMC molecules and CO2 molecules, and the calculation method is as follows:

[0128]

[0129]

[0130] In the formula: is the standard evaporation free energy of DMC molecules, unit: J / mol; is the standard evaporation free energy of CO2 molecules, unit: J / mol, is the standard Gibbs free energy of DMC molecules in air, is the standard Gibbs free energy of DMC molecules in the electrolyte, is the standard Gibbs free energy of CO2 molecules in air, is the standard Gibbs free energy of CO2 molecules in the electrolyte.

[0131] Step 5: Construct a combustion elementary reaction model for the thermal decomposition process of DMC, and calculate the standard reaction Gibbs free energy of each elementary reaction. Construct an elementary reaction model for the thermal decomposition of DMC in the electrolyte environment and air environment, and calculate the standard reaction Gibbs free energy of each elementary reaction under the conditions of the electrolyte environment and air environment. Taking the calculation of the standard reaction Gibbs free energy of the first-step elementary reaction of DMC molecule thermal decomposition in the electrolyte environment as an example, the calculation process is as follows:

[0132] CH3OCOOCH3 → CH3OCOOCH2· + H·

[0133]

[0134] In the formula: represents the standard reaction Gibbs free energy of the CH3OCOOCH2· group in the solution, unit: J / mol; represents the standard reaction Gibbs free energy of the H· group in the solution, unit: J / mol, represents the standard reaction Gibbs free energy of the CH3OCOOCH3 molecule in the solution, unit: J / mol.

[0135] Step 6: Construct a chain chemical reaction model for the thermal decomposition of DMC. Construct a chain chemical reaction model for the thermal decomposition process of DMC under the conditions of the electrolyte environment and air environment respectively, and draw a thermal decomposition reaction path diagram, as Figure 3a 、 Figure 3b shown.

[0136] Step 7: Calculate the reaction Gibbs free energy of each elementary reaction in the DMC thermal decomposition process at different temperatures. Based on the elementary reactions in the DMC thermal decomposition reaction path obtained in Step 6, and using quantum chemical methods, calculate the Gibbs free energy correction factor G of each group in the elementary reaction at m (m≥5) temperature points from 200K to 1000K 校正-T , and calculate the Gibbs free energy G of each group at each temperature point T , and fit to obtain G T as a curve of variation with temperature;

[0137] Based on the DMC thermal decomposition reaction path, calculate the reaction Gibbs free energy ΔG of each elementary reaction at m temperature points from 200K to 1000K T , and fit to obtain ΔG T as a curve of variation with temperature. Taking the calculation of the standard reaction Gibbs free energy of the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment as an example, the calculation process is as follows, G T and ΔG T fitting curves are as shown in Figure 4a , 4b , 4c, 4d:

[0138]

[0139]

[0140]

[0141]

[0142] In the formula: represents the reaction Gibbs free energy of CH3OCOOCH3 molecule in solution at temperature T, unit, J / mol; represents the electronic energy of CH3OCOOCH3 molecule in solution environment, unit, J / mol; represents the reaction Gibbs free energy correction factor of CH3OCOOCH3 molecule in solution at temperature T, unit, J / mol; represents the reaction Gibbs free energy of CH3OCOOCH2· group in solution at temperature T, unit, J / mol; represents the electronic energy of CH3OCOOCH2· group in solution environment, unit, J / mol; represents the reaction Gibbs free energy correction factor of CH3OCOOCH2· group in solution at temperature T, unit, J / mol; represents the reaction Gibbs free energy of H· group in solution at temperature T, unit, J / mol; represents the electronic energy of the H· group in a solution environment, unit: J / mol; represents the reaction Gibbs free energy correction factor of the H· group in solution at temperature T, unit: J / mol.

[0143] Step Eight: Calculation of the fire kinetics parameters for the elementary reaction of DMC thermal decomposition. It is completed in the following four steps. The fire kinetics parameters are calculated for the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment.

[0144] First Step: Obtain the curves of the Gibbs free energy of each elementary reaction varying with temperature fitted in Step Seven, as shown in Figure 4a , 4b , 4c, and 4d. Fit the fire kinetics parameters according to the Arrhenius equation. The specific calculation process is as follows:

[0145]

[0146] Take the logarithm of both sides of the above formula, then differentiate with respect to temperature T, and substitute it into the differential form of the Arrhenius equation to obtain:

[0147] E T = E0 + nRT

[0148] E T = ΔG T

[0149] Plot the curve of E T versus temperature T and perform linear fitting. The fitting form is:

[0150] E T = aT + b, R 2

[0151] The fitting formula for the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment is as follows:

[0152] E T = -139.97T + 427086, R 2 = 0.9993

[0153] Second Step: Calculate the activation energy and temperature coefficient of the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment. From the fitting curve obtained in the first step, we can get:

[0154] E0 = 427086

[0155] n = -139.97 ÷ 8.314 = -16.84

[0156] Step 3: Calculate the rate constant of the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment. At the temperature T obtained in Step 7, the reaction Gibbs free energy ΔG of the elementary reaction is used to calculate the reaction rate constant k of the elementary reaction at temperature T. T The reaction rate constant k of the elementary reaction at temperature T is calculated as follows: T :

[0157]

[0158] The reaction rate constant at 200K for the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment is calculated from the reaction Gibbs free energy at 200K as follows:

[0159]

[0160] Step 4: Calculate the pre-exponential factor of the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment. According to the Arrhenius equation, substitute the activation energy E0, temperature coefficient n, and reaction rate constant k at temperature T obtained in Steps 2 and 3. T We get:

[0161]

[0162] The pre-exponential factor of the first elementary reaction of DMC molecule thermal decomposition in the electrolyte environment is calculated from the fire kinetic parameters at 200K as follows:

[0163]

[0164] Similarly, using the above method, the fire kinetic parameters of the elementary reaction process of DMC molecule thermal decomposition in the solution and air environments in commercial electrolytes are calculated, and the results are shown in Table 2 below:

[0165] Table 2

[0166]

[0167] Directly import the generated combustion elementary reaction model, chain chemical reaction model of each component of the electrolyte, and fire kinetic parameters in the experimental examples of the present invention into programs such as the combustion kinetics analysis software CHMEKIN and the fire computational fluid dynamics software ANSYS FLUENT in the form of txt text files to obtain the numerical simulation results of lithium-ion battery fires and the fire hazard assessment results of lithium-ion batteries.

[0168] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) that contain computer-usable program code.

[0169] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce means for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0170] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that implement the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0171] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or the combination of blocks.

[0172] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, they can also make several substitutions or modifications to these described embodiments, and these substitution or modification methods should all be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. Without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for determining the fire kinetic parameters of a lithium-ion battery electrolyte, characterized in that, It includes the following steps: S1: Construct an electrolyte group model and obtain electrolyte environment parameters; S2: Obtain the evaporation free energy and the standard reaction Gibbs free energy of each elementary reaction according to the electrolyte group model and the electrolyte environment parameters; S3: Construct a combustion elementary reaction model based on the electrolyte group model; S4: Construct a chain chemical reaction model of each component of the electrolyte based on the combustion elementary reaction model, the evaporation free energy, and the standard reaction Gibbs free energy of each elementary reaction, and calculate the reaction Gibbs free energy of each elementary reaction at different temperatures; S5: Determine the fire kinetics parameters according to the reaction Gibbs free energy of each elementary reaction at different temperatures; Among them, step S5 includes: S51: Fit and obtain the curve of the activation energy of the elementary reaction at different temperatures changing with temperature based on the reaction Gibbs free energy of the elementary reaction at different temperatures; S52: Calculate the activation energy and temperature coefficient of each elementary reaction according to the curve of the activation energy of the elementary reaction at different temperatures changing with temperature; S53: Obtain the reaction rate constant of the elementary reaction according to the curve of the activation energy of the elementary reaction at different temperatures changing with temperature and the activation energy and temperature coefficient of each elementary reaction; S54: Obtain the pre-exponential factor of the elementary reaction according to the activation energy and temperature coefficient of each elementary reaction and the reaction rate constant of the elementary reaction; The reaction rate constant of the elementary reaction is expressed by the following formula: Among them, σ is the reaction path degeneracy, k B is the Boltzmann constant, h is the Planck constant, T is the temperature, and ΔG T is the reaction Gibbs free energy of the elementary reaction, and R is the gas constant; The pre-exponential factor of the elementary reaction is expressed by the following formula: where k T is the reaction rate constant of the elementary reaction, E0 is the activation energy of the fire kinetics parameter, n is the temperature coefficient, T is the temperature, and R is the gas constant.

2. The method according to claim 1, wherein Step S2 includes: S21. Obtain the Gibbs free energy correction factor according to the electrolyte group model and the electrolyte environment parameters, and calculate the standard Gibbs free energy of each group in the two environments of electrolyte and air; S22: Obtain the evaporation free energy of the gas group and the standard reaction Gibbs free energy of each elementary reaction based on the standard Gibbs free energy.

3. The method according to claim 1, characterized in that, In step S4, the construction of the chain chemical reaction model of each component of the electrolyte includes: respectively constructing the chain chemical reaction model of each component of the electrolyte under the electrolyte environment conditions and the air environment conditions, and using the standard reaction Gibbs free energy of each elementary reaction as a measurement standard to judge whether the construction of the chain chemical reaction model of each component of the electrolyte is reasonable.

4. The method according to claim 1, characterized in that, In step S1, the electrolyte environment parameters include the dielectric constant of the electrolyte solution environment, and the quantum chemical calculation solution solvent model parameters are set according to the dielectric constant of the electrolyte solution environment.

5. The method according to claim 1, wherein In step S5, the reaction Gibbs free energy of each elementary reaction at different temperatures is the Gibbs free energy of the reaction of each elementary reaction at m temperature points from 200K to 1000K, where m≥5.

6. The method according to claim 1, wherein The electrolyte group model in step S1 includes the thermal decomposition and combustion models under the electrolyte environment and the thermal decomposition and combustion models under the air environment.

7. A method for evaluating the fire hazard of a lithium-ion battery, characterized in that, It includes the following steps: A1: Input the combustion elementary reaction model, the chain chemical reaction model of each component of the electrolyte, and the fire kinetics parameters in the method described in any one of claims 1-6 into the fluid mechanics fire numerical simulation program to obtain the lithium-ion battery fire numerical simulation results; A2: Obtain the lithium-ion battery fire hazard assessment results according to the lithium-ion battery fire numerical simulation results.

8. A computer-readable medium having a computer program stored thereon, characterized in that, When the described program is executed by a processor, it implements the steps of the method according to any one of claims 1-6.

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