Three-dimensional lithium battery electrothermal coupling computer aging analysis method and system

Abstract

The invention relates to the technical field of new energy, in particular to a three-dimensional lithium battery electrothermal coupling computer aging analysis method and system. Compared with a lithium ion battery P2D model which is widely used at present, the lithium ion battery P2D model has the advantages that the fitting result of the model on experimental data in the aspects of discharge voltage and surface temperature is obviously better, and battery aging data can be reproduced. And coupling the three-dimensional electrochemical model with the two-dimensional thermal model. According to the model, an SEI film formed on the surface of the graphite particles and aging behaviors caused by metal lithium plating are considered, so that the model precision is higher. The influence of SEI film and metal Li deposition on the model is considered. By establishing a more comprehensive and accurate three-dimensional coupling model and considering a key aging mechanism, accurate prediction of the performance and the service life of the lithium battery is realized. The prediction capability is of great significance to optimization of battery design, improvement of a thermal management strategy and prolonging of the service life of the battery. Compared with a traditional method, the prediction result of the method is closer to the actual situation, and more reliable theoretical guidance is provided for research, development and application of the battery.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a three-dimensional lithium battery electrothermal coupling computer aging analysis method and system. Background Art

[0002] At present, lithium-ion batteries, as an excellent energy storage carrier of new energy under the dual carbon goals, have been widely used in various aspects of social life and serve as core energy storage components in recent years due to their advantages such as high power density and energy density, long cycle life and low environmental pollution. At present, when lithium-ion batteries are used as energy storage batteries, there are still problems such as thermal runaway, which not only poses a safety hazard, but also greatly reduces the life of the battery. Therefore, achieving efficient and accurate control of battery thermal management is of great significance for the further development of lithium batteries and the timely realization of the dual carbon plan. At present, most existing electrochemical-thermal models—commercial and non-commercial—are established by using this P2D model, which is used to simulate electrochemical kinetics and estimate the heat generated. Thereafter, this heat is used as input to a two-dimensional (2D) or three-dimensional (3D) thermal model to calculate the battery temperature distribution. However, with this approach, the effects of battery inhomogeneity and current flow in the electrode plane are ignored. This approximation may be reasonable for small-scale batteries with simple designs, but should be used with caution for large-scale batteries where the global geometry is usually non-planar. This is especially true for cylindrical cells, which are manufactured by winding long thin anode assembly films to obtain a relatively large effective area-to-volume ratio. Since cylindrical cells usually have only one pair of tabs, the current flows over a considerable distance before being collected by the other tab, which naturally causes a potential drop across the cell. From a thermal management perspective, this will result in a certain amount of heat generation from the electronic resistance of the current collector. And since the structure of cylindrical cells is somewhat complex, a fully coupled 3D electrochemical-thermal model becomes resource- and time-consuming. Therefore, for cylindrical cells, these effects of the in-plane resistance of the current collector are rarely analyzed by computation. In addition, a direct result of increased temperature is accelerated battery aging. However, in experiments and modeling on battery aging, most studies are conducted by applying a fixed external temperature, rather than studying the in-situ effects of battery self-heating. Therefore, in this study, we established a more comprehensive model for commercial cylindrical batteries by coupling a 3D electrochemical model with a 2D axisymmetric heat transfer model. The electrochemical model is based on a disassembled battery structure and takes into account the temperature-dependent aging dynamics. This coupled model can not only analyze the thermal behavior of the battery, but also explain and predict the battery aging behavior. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention is proposed.

[0004] Therefore, the problem to be solved by the present invention is how to ignore the effects of battery inhomogeneity and current flow in the electrode plane through the P2D model method. This approximation may be reasonable for small-scale batteries with simple designs, but should be used with caution for large-scale batteries where the global geometry is usually non-planar. This is especially true for cylindrical batteries, which are manufactured by winding long thin anode assembly films to obtain a relatively large effective area-to-volume ratio. Since cylindrical batteries usually have only one pair of tabs, the current flows over a considerable distance before being collected by the other tab, which naturally leads to a potential drop across the battery.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] In a first aspect, an embodiment of the present invention provides a three-dimensional lithium battery electrothermal coupling computer aging analysis method, which includes establishing a three-dimensional electrochemical model, obtaining the diffusion of lithium ions in the solid phase and the liquid phase, the movement of electrons in the solid phase and the liquid phase, and calculating the battery temperature through heat dissipation and heat generation;

[0007] A two-dimensional axisymmetric heat conduction model was established to calculate the temperature distribution of cylindrical batteries;

[0008] The three-dimensional electrochemical model is coupled with the two-dimensional thermal model to obtain a coupled model, the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the two-dimensional thermal model is used as the input of the three-dimensional electrochemical model;

[0009] Simulate the battery aging process, including the SEI film formation reaction and the reaction of metal lithium deposition;

[0010] Solve the coupling model to obtain the performance parameters of the battery's voltage, temperature distribution and capacity attenuation, and compare them with the actual data to verify the accuracy of aging prediction.

[0011] As a preferred solution of the three-dimensional lithium battery electrothermal coupling computer aging analysis method of the present invention, wherein: the establishment of a three-dimensional electrochemical model includes mass conservation, charge conservation and energy conservation, the diffusion of lithium ions in the solid phase and the liquid phase is obtained by mass conservation, the movement of electrons in the solid phase and the liquid phase is obtained by charge conservation, the battery temperature is calculated by heat dissipation and heat generation by energy conservation, and the mass conservation is obtained by mass transfer of Li embedded in active solid particles by using Fick's second law of spherical coordinates, which adopts the following expression:

[0012]

[0013] Where t is the time, r is the pseudo radial coordinate along the active spherical particle, Cs is the concentration of embedded Li in the solid phase, and Ds is the diffusion coefficient of embedded Li in the solid phase;

[0014] Considering the boundary conditions at the center and surface of the particle, the boundary conditions can be easily obtained by the expression of the lithium ion concentration gradient at the center and boundary of the electrode particle according to Fick's first law, and the following expression can be used:

[0015]

[0016] Among them, j L is the diffusion flux of lithium ions, r is the pseudo-radial coordinate along the active spherical particle, Cs is the concentration of embedded Li in the solid phase, and Ds is the diffusion coefficient of embedded Li in the solid phase;

[0017] The mass conservation of lithium ions in the liquid phase follows the concentrated electrolyte theory. Assuming that the electrolyte is a binary system, diffusion and migration can change the local lithium ion concentration, and the following expression is used:

[0018]

[0019] Among them, ε e represents the liquid volume fraction, C l is the Li ion concentration in the electrolyte; is the effective diffusion coefficient in the electrolyte, i l is the current density in the electrolyte; R source It is a source or sink of lithium ions caused by different reactions, including lithium insertion and deinsertion and side reactions involving lithium ions;

[0020] Since there is no Li ion source or sink at the interface between the current collector and the active material, the corresponding boundary condition can be expressed as follows:

[0021]

[0022] Among them, C l is the Li ion concentration in the electrolyte; L neg is the thickness of the negative electrode, L sep is the diaphragm thickness; L pos is the thickness of the positive electrode; L neg -cc is the negative collector thickness.

[0023] As a preferred solution of the three-dimensional lithium battery electrothermal coupling computer aging analysis method of the present invention, wherein: the establishment of the three-dimensional electrochemical model includes mass conservation, charge conservation and energy conservation, and the movement of electrons in the solid phase and the liquid phase is obtained by charge conservation. For the charge balance part, in the solid phase materials of the positive and negative electrodes, the relationship between the potential and the current can be obtained according to Ohm's law, and the current is equal to the gradient of the negative potential multiplied by the conductivity, which is specifically expressed as follows:

[0024]

[0025] Among them, i s Yes, among which, i s is the current density in the solid phase, is the effective conductivity in the solid phase; is the solid phase potential;

[0026] At the same time, according to Faraday's law of electrolysis, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF. The change in solid-phase current can be related to the concentration of lithium ions participating in the electrode reaction. The specific relationship between the diffusion flux and the solid-phase transport current is as follows:

[0027]

[0028] Among them, a s is the specific surface area, F is the Faraday constant; j L is the diffusion flux of lithium ions;

[0029] Combining the above two expressions of Ohm's law of solid phase and Faraday's law of electrolysis, the relationship between solid phase potential and diffusion flux is as follows:

[0030]

[0031] Among them, a s is the specific surface area: It indicates the reaction area of ​​electrode active material per unit volume; is the solid phase potential; it represents the reaction area of ​​the electrode active material per unit volume; at the same time, the solid phase potential at the boundary with the negative electrode current collector is defined as 0. Since the diaphragm is composed of inert materials, only ions are allowed to pass through, while charges cannot pass through the diaphragm. Therefore, no charge passes through the interface between the two sides of the diaphragm and the solid. The following expression is used:

[0032]

[0033] in, is the solid phase potential; is the liquid phase potential; is the effective conductivity of the solid phase; the charge flux at the junction of the current collector and the positive electrode is the current density of the battery I app , using the following expression:

[0034]

[0035] Among them, I app is the current density of the battery, It is liquid-phase television; is the effective conductivity of the solid phase; in the electrolyte, the charge balance is composed of Ohm's law and the migration potential, using the following expression:

[0036]

[0037] In the above formula, the second phase on the right side represents the effect of the lithium ion concentration in the liquid phase on the lithium ion concentration in the liquid phase, which represents the directional movement of lithium ions under concentration polarization, and the second phase on the right side represents the effect of the liquid phase potential on the lithium ion concentration, which conforms to the description of Ohm's law.

[0038] Similarly, according to Faraday's law of electrolysis, that is, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF, the change in liquid phase current is linked to the concentration of lithium ions participating in the electrode reaction, and finally the relationship between the diffusion flux and the liquid phase transport current is obtained as shown in the following equation:

[0039]

[0040] Finally, according to Ohm's law of liquid phase and Faraday's law of electrolysis, the relationship between diffusion flux and liquid phase current can be obtained as shown in the following formula:

[0041]

[0042] in, is the liquid effective conductivity, is the liquid phase potential; R is the thermodynamic constant; T is the temperature; F is the Faraday constant; C e is the liquid phase lithium ion concentration.

[0043] As a preferred solution of the three-dimensional lithium battery electrothermal coupling computer aging analysis method of the present invention, wherein: the establishment of a three-dimensional electrochemical model includes mass conservation, charge conservation and energy conservation, the battery temperature is calculated by heat dissipation and heat generation through energy conservation, and energy conservation during operation. There are three different main heat sources in lithium-ion batteries: ohmic heat, activation polarization heat and reaction heat. The total energy conservation of the battery can be expressed as follows:

[0044]

[0045] Where ρ is the battery material density; C p is the specific heat capacity of the battery; k T is the thermal conductivity; Q ohm is Ohmic heat, Q act is the activation polarization heat, Q react is the heat of reaction, ρ, C p , k T are the density, heat capacity and thermal conductivity of the materials in the corresponding computational domains, respectively; in this model, the outer container (steel), core (nylon) and active electrode domain (scroll) are considered;

[0046] The scroll structure is assumed to be a homogeneous domain with anisotropic thermal conductivity, which can be calculated by lumped properties of different layers in parallel (kT,ang) or in series (kT,r); three different types of heat sources can be calculated as follows:

[0047] Q act =a s Fj L η=a s i s (φ s -φ e -E ocv )

[0048]

[0049] in, is the liquid phase potential; E o cv is the open circuit voltage or the potential at equilibrium; η is the overpotential of the electrode;

[0050] The cooling condition applied to the outer container surface is defined as:

[0051]

[0052] Among them, k T,out is the thermal conductivity of the external container, h is its heat transfer coefficient to the environment, and Tamb is the ambient temperature.

[0053] As a preferred solution of the three-dimensional lithium battery electrothermal coupling computer aging analysis method of the present invention, wherein: the three-dimensional electrochemical model is coupled with the two-dimensional thermal model to obtain a coupled model, the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the two-dimensional thermal model is used as the input of the three-dimensional electrochemical model;

[0054] The aging behavior caused by the formation of SEI film and metal lithium plating on the surface of graphite particles is considered in the dimensional electrochemical model. In addition to the expected Li insertion and deinsertion, there are two reactions that consume cyclable Li, and it is assumed that these two reactions proceed along the electrochemical activity.

[0055] Lithium insertion and deintercalation: The reaction rates of conventional intercalation and deintercalation reactions can be expressed using the Butler-Volmer equation as follows:

[0056]

[0057] Where n is the charge number of the ion; α a is the positive electrode transfer coefficient; α c is the negative electrode transfer coefficient;

[0058]

[0059] Among them, η represents the overpotential of the electrode, which is used to describe the change in potential caused by the embedding and migration of lithium ions in the electrode particles. Its expression is:

[0060] η=φ s -φ l -E ocv -Δφ s,film

[0061] where φ l is the liquid phase potential; Δφ s,film is caused by the surface resistance of the side reaction product film, where E ocv is the open circuit voltage or the potential at equilibrium.

[0062] As a preferred solution of the three-dimensional lithium battery electrothermal coupling computer aging analysis method of the present invention, wherein: the simulation of the battery aging process includes considering the SEI film formation reaction and the reaction of metal lithium deposition;

[0063] SEI formation: Here, it is assumed that SEI formation is the electrochemical reduction of the electrolyte, and the following expression is used:

[0064] S+Li + +e - →P SEI

[0065] Where S is the electrolyte solvation reactant, P SEI It is a reduction product;

[0066] The product is precipitated on the surface of the graphite particles to form a SEI layer; the reaction rate of SEI formation can be calculated according to the cathode Tafel equation, as shown in the following formula:

[0067]

[0068] Among them, K SEI is the reaction rate constant, is the lithium ion concentration on the surface of the electrode particles; C l，0 is the initial lithium ion concentration in the liquid phase; Co (1-α) is the difference between the maximum lithium insertion concentration and the lithium ion concentration on the electrode surface;

[0069] The Arrhenius equation was used to model the temperature-dependent kinetics:

[0070]

[0071] In addition, SEI formation is limited by the mass transport of substances through the SEI layer. Considering that the transport of electrolyte molecular substances is more difficult than the transport of electrons, it is assumed here that SEI growth occurs at the interface between the SEI layer and the electrolyte, that is, toward the electrolyte. Then, the growth rate is limited by the transport of electrons through the SEI layer. The limiting current density can be calculated by the equation as shown below:

[0072]

[0073] Where D e_SEI·F is the diffusion coefficient of electrons in the SEI phase, which can be calculated by the following formula:

[0074]

[0075] By using this Arrhenius formula, the effect of temperature can be integrated into the SEI for recrystallization kinetics and then the final formation rate of the SEI can be calculated:

[0076]

[0077] Among them, i form，SEI is the SEI film growth rate; i F，SEI is the Faraday constant for the formation of SEI film; i lim It is the limiting current density caused by electron transport in the SEI layer;

[0078] Metal Li deposition: There is no free site required for Li insertion in metal Li deposition, and the formation rate of metal Li can also be calculated by the cathode Tafel equation:

[0079]

[0080] Among them, K Li Here is the rate constant, and it also needs to be corrected by the Arrhenius formula:

[0081]

[0082] Among them, E a，Li is the activation energy of the lithium plating reaction rate constant.

[0083] As a preferred solution of the three-dimensional lithium battery electrothermal coupling computer aging analysis method of the present invention, wherein: the coupling model is solved to obtain the performance parameters of the battery's voltage, temperature distribution and capacity decay, which are compared with the realized data to verify the accuracy of aging prediction; all three electrochemical reactions mentioned above occur in parallel and simultaneously on the surface of graphite particles, competing for Li in the system. Assuming that SEI formation and Li deposition occur only during charging, the consumption of cyclable Li caused by side reactions will lead to battery capacity decay, and the formed SEI layer increases the potential drop on the electrode interface, both of which will lead to battery aging.

[0084] In a second aspect, an embodiment of the present invention provides a three-dimensional lithium battery electrothermal coupling computer aging analysis system, which includes a construction module, establishes a three-dimensional electrochemical model, obtains the diffusion of lithium ions in the solid phase and the liquid phase, the movement of electrons in the solid phase and the liquid phase, and calculates the battery temperature through heat dissipation and heat generation;

[0085] The calculation module establishes a two-dimensional axisymmetric heat conduction model to calculate the temperature distribution of cylindrical batteries;

[0086] A coupling module couples the three-dimensional electrochemical model with the two-dimensional thermal model to obtain a coupling model, wherein the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the two-dimensional thermal model is used as the input of the three-dimensional electrochemical model;

[0087] Simulation module, which simulates the battery aging process, including the consideration of SEI film formation reaction and metal lithium deposition reaction;

[0088] The verification module solves the coupling model to obtain the performance parameters of the battery’s voltage, temperature distribution, and capacity attenuation, and compares them with the realized data to verify the accuracy of the aging prediction.

[0089] In a third aspect, an embodiment of the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program instructions are executed by the processor, the steps of the three-dimensional lithium battery electrothermal coupling computer aging analysis method as described in the first aspect of the present invention are implemented.

[0090] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program instructions are executed by a processor, the steps of the three-dimensional lithium battery electrothermal coupling computer aging analysis method as described in the first aspect of the present invention are implemented.

[0091] The beneficial effects of the present invention are as follows: compared with the currently widely used P2D model of lithium-ion batteries, the model has significantly better fitting results for experimental data in terms of discharge voltage and surface temperature, and can reproduce battery aging data. The three-dimensional electrochemical model is coupled with the two-dimensional thermal model. The model takes into account the aging behavior caused by the formation of SEI film on the surface of graphite particles and the plating of metallic lithium, so the model is more accurate. The influence of SEI film and metallic Li deposition on the model is taken into account.

[0092] By establishing a three-dimensional electrochemical model, the diffusion of lithium ions in the solid and liquid phases, the movement of electrons in the solid and liquid phases, and the calculation of battery temperature were obtained. Compared with the traditional two-dimensional model, this three-dimensional model can more accurately describe the electrochemical reaction and heat conduction process inside the battery, improving the accuracy of the model.

[0093] By establishing a two-dimensional axisymmetric heat conduction model, the temperature distribution of cylindrical batteries can be calculated. This specific thermal model for cylindrical battery structures can better reflect the temperature distribution characteristics of actual batteries and help analyze hot spot locations.

[0094] The three-dimensional electrochemical model is coupled with the two-dimensional thermal model to form a complete coupled model. This coupling can reflect the mutual influence between the electrochemical reaction and the thermal effect, is closer to the actual working state of the battery, and improves the authenticity of the simulation.

[0095] When simulating the battery aging process, the SEI film formation reaction and the metal lithium deposition reaction are taken into account. These two reactions are key factors affecting battery aging, and their inclusion in the model can more accurately predict the long-term performance degradation of the battery.

[0096] By solving the coupling model, the battery's voltage, temperature distribution, capacity attenuation and other performance parameters are obtained, and then compared with experimental data for verification. This method can not only predict battery performance, but also continuously optimize the model through experimental verification to improve prediction accuracy.

[0097] In summary, this method achieves accurate prediction of lithium battery performance and life by establishing a more comprehensive and accurate three-dimensional coupling model and taking into account key aging mechanisms. This prediction capability is of great significance for optimizing battery design, improving thermal management strategies, and extending battery life, and helps to improve the overall level of new energy battery technology. Compared with traditional methods, the prediction results of this method are closer to the actual situation, providing more reliable theoretical guidance for battery research and development and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0099] Figure 1 It is a flow chart of the three-dimensional lithium battery electrothermal coupling computer aging analysis method;

[0100] Figure 2 Computer equipment diagram for three-dimensional lithium battery electrothermal coupling computer aging analysis method. DETAILED DESCRIPTION

[0101] In order to make the above-mentioned objects, 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 accompanying drawings.

[0102] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0103] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0104] Example 1

[0105] Reference Figure 1-2 , which is the first embodiment of the present invention, provides a three-dimensional lithium battery electrothermal coupling computer aging analysis method, including:

[0106] S100: Establish a three-dimensional electrochemical model to obtain the diffusion of lithium ions in the solid and liquid phases, the movement of electrons in the solid and liquid phases, and calculate the battery temperature through heat dissipation and heat generation;

[0107] S101: The three-dimensional electrochemical model is established, including mass conservation, charge conservation and energy conservation. The diffusion of lithium ions in the solid phase and the liquid phase is obtained by mass conservation, the movement of electrons in the solid phase and the liquid phase is obtained by charge conservation, and the battery temperature is calculated by heat dissipation and heat generation by energy conservation. The mass conservation is obtained by mass transfer of Li embedded in active solid particles through Fick's second law using spherical coordinates, which uses the following expression:

[0108]

[0109] Where t is the time, r is the pseudo radial coordinate along the active spherical particle, Cs is the concentration of embedded Li in the solid phase, and Ds is the diffusion coefficient of embedded Li in the solid phase;

[0110] Considering the boundary conditions at the center and surface of the particle, the boundary conditions can be easily obtained by the expression of the lithium ion concentration gradient at the center and boundary of the electrode particle according to Fick's first law, and the following expression can be used:

[0111]

[0112] Among them, j L is the diffusion flux of lithium ions, r is the pseudo-radial coordinate along the active spherical particle, Cs is the concentration of embedded Li in the solid phase, and Ds is the diffusion coefficient of embedded Li in the solid phase;

[0113] The mass conservation of lithium ions in the liquid phase follows the concentrated electrolyte theory. Assuming that the electrolyte is a binary system, diffusion and migration can change the local lithium ion concentration, and the following expression is used:

[0114]

[0115] Among them, ε e Indicates that C l is the Li ion concentration in the electrolyte; is the effective diffusion coefficient in the electrolyte, i l is the current density in the electrolyte; R source It is a source or sink of lithium ions caused by different reactions, including lithium insertion and deinsertion and side reactions involving lithium ions;

[0116] Since there is no Li ion source or sink at the interface between the current collector and the active material, the corresponding boundary condition can be expressed as follows:

[0117]

[0118] Among them, ε e represents the liquid volume fraction, C l is the Li ion concentration in the electrolyte; is the effective diffusion coefficient in the electrolyte, i l is the current density in the electrolyte; R source It is a source or sink of lithium ions caused by different reactions, including lithium insertion and deinsertion and side reactions involving lithium ions;

[0119] Since there is no Li ion source or sink at the interface between the current collector and the active material, the corresponding boundary condition can be expressed as follows:

[0120]

[0121] Among them, C l is the Li ion concentration in the electrolyte; L neg is the thickness of the negative electrode, L sep is the diaphragm thickness; L pos is the thickness of the positive electrode; L neg -cc is the negative collector thickness;

[0122] At the same time, according to Faraday's law of electrolysis, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF. The change in solid-phase current can be related to the concentration of lithium ions participating in the electrode reaction. The specific relationship between the diffusion flux and the solid-phase transport current is as follows:

[0123]

[0124] Among them, i s is the current density in the solid phase, is the effective conductivity in the solid phase; is the solid phase potential;

[0125] At the same time, according to Faraday's law of electrolysis, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF. The change in solid-phase current can be related to the concentration of lithium ions participating in the electrode reaction. The specific relationship between the diffusion flux and the solid-phase transport current is as follows:

[0126]

[0127] Among them, a s is the specific surface area, F is the Faraday constant; j L is the diffusion flux of lithium ions;

[0128] Combining the above two expressions of Ohm's law of solid phase and Faraday's law of electrolysis, the relationship between solid phase potential and diffusion flux is as follows:

[0129]

[0130] Among them, a s is the specific surface area: It indicates the reaction area of ​​electrode active material per unit volume; is the solid phase potential; it represents the reaction area of ​​the electrode active material per unit volume; at the same time, the solid phase potential at the boundary with the negative electrode current collector is defined as 0. Since the diaphragm is composed of inert materials, only ions are allowed to pass through, while charges cannot pass through the diaphragm. Therefore, no charge passes through the interface between the two sides of the diaphragm and the solid. The following expression is used:

[0131]

[0132] in, is the solid phase potential; is the liquid phase potential; is the effective conductivity of the solid phase; the charge flux at the junction of the current collector and the positive electrode is the current density of the battery I app , using the following expression:

[0133]

[0134] Among them, I app is the current density of the battery, It is liquid-phase television; is the effective conductivity of the solid phase; in the electrolyte, the charge balance is composed of Ohm's law and the migration potential, using the following expression:

[0135]

[0136] In the above formula, the second phase on the right side represents the effect of the lithium ion concentration in the liquid phase on the lithium ion concentration in the liquid phase, which represents the directional movement of lithium ions under concentration polarization, and the second phase on the right side represents the effect of the liquid phase potential on the lithium ion concentration, which conforms to the description of Ohm's law.

[0137] Similarly, according to Faraday's law of electrolysis, that is, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF, the change in liquid phase current is linked to the concentration of lithium ions participating in the electrode reaction, and finally the relationship between the diffusion flux and the liquid phase transport current is obtained as shown in the following equation:

[0138]

[0139] Finally, according to Ohm's law of liquid phase and Faraday's law of electrolysis, the relationship between diffusion flux and liquid phase current can be obtained as shown in the following formula:

[0140]

[0141] in, is the liquid effective conductivity, is the liquid phase potential; R is the thermodynamic constant; T is the temperature; F is the Faraday constant; C e is the liquid phase lithium ion concentration.

[0142] S200: Establish a two-dimensional axisymmetric heat conduction model to calculate the temperature distribution of cylindrical batteries;

[0143] S201: The three-dimensional electrochemical model is established, including mass conservation, charge conservation and energy conservation. The battery temperature is calculated by heat dissipation and heat generation through energy conservation. During the operation of energy conservation, there are three different main heat sources in lithium-ion batteries: ohmic heat, activation polarization heat and reaction heat. The total energy conservation of the battery can be expressed as follows:

[0144]

[0145] Where ρ is the battery material density; C p is the specific heat capacity of the battery; k T is the thermal conductivity; ohm is ohmic heat, Q act is the activation polarization heat, Q react is the heat of reaction, ρ, C p , k T are the density, heat capacity and thermal conductivity of the materials in the corresponding computational domains, respectively; in this model, the outer container (steel), core (nylon) and active electrode domain (scroll) are considered;

[0146] The scroll structure is assumed to be a homogeneous domain with anisotropic thermal conductivity, which can be calculated by lumped properties of different layers in parallel (kT,ang) or in series (kT,r); three different types of heat sources can be calculated as follows:

[0147] Q act =a s Fj L η=a s i s (φ s -φ e -E ocv )

[0148]

[0149] in, is the liquid phase potential; E o cv is the open circuit voltage or the potential at equilibrium; η is the overpotential of the electrode;

[0150] The cooling condition applied to the outer container surface is defined as:

[0151]

[0152] Among them, k T,out is the thermal conductivity of the external container, h is its heat transfer coefficient to the environment, and Tamb is the ambient temperature.

[0153] S300: coupling the three-dimensional electrochemical model with the two-dimensional thermal model to obtain a coupled model, wherein the heat calculated by the three-dimensional electrochemical model is used as an input to the two-dimensional thermal model, and the average temperature calculated by the two-dimensional thermal model is used as an input to the three-dimensional electrochemical model;

[0154] S301: coupling the three-dimensional electrochemical model with the two-dimensional thermal model to obtain a coupled model, using the heat calculated by the three-dimensional electrochemical model as input to the two-dimensional thermal model, and using the average temperature calculated by the two-dimensional thermal model as input to the three-dimensional electrochemical model;

[0155] The aging behavior caused by the formation of SEI film and metal lithium plating on the surface of graphite particles is considered in the dimensional electrochemical model. In addition to the expected Li insertion and deinsertion, there are two reactions that consume cyclable Li, and it is assumed that these two reactions proceed along the electrochemical activity.

[0156] Lithium insertion and deintercalation: The reaction rates of conventional intercalation and deintercalation reactions can be expressed using the Butler-Volmer equation as follows:

[0157]

[0158] where n is the charge number of the ion; α a is the positive electrode transfer coefficient; α c is the negative electrode transfer coefficient;

[0159]

[0160] Among them, η represents the overpotential of the electrode, which is used to describe the change in potential caused by the embedding and migration of lithium ions in the electrode particles. Its expression is:

[0161] η=φ s -φ l -E ocv -Δφ s,film

[0162] Where, is the liquid potential; Δφ s,film is caused by the surface resistance of the side reaction product film, where E ocv is the open circuit voltage or the potential at equilibrium.

[0163] S400: Simulates the battery aging process, including the SEI film formation reaction and the reaction of metal lithium deposition;

[0164] S401: The simulation of the battery aging process includes considering the SEI film formation reaction and the metal lithium deposition reaction;

[0165] SEI formation: Here, it is assumed that SEI formation is the electrochemical reduction of the electrolyte, and the following expression is used:

[0166] S+Li+ +e - →P SEI

[0167] Where S is the electrolyte solvation reactant, P SEI It is a reduction product;

[0168] The product is precipitated on the surface of the graphite particles to form a SEI layer; the reaction rate of SEI formation can be calculated according to the cathode Tafel equation, as shown in the following formula:

[0169]

[0170] Among them, K SEI is the reaction rate constant, is the lithium ion concentration on the surface of the electrode particles; C l , 0 is the initial lithium ion concentration in the liquid phase; Co (1-α) is the difference between the maximum lithium insertion concentration and the lithium ion concentration on the electrode surface;

[0171] The Arrhenius equation was used to model the temperature-dependent kinetics:

[0172]

[0173] In addition, SEI formation is limited by the mass transport of substances through the SEI layer. Considering that the transport of electrolyte molecular substances is more difficult than the transport of electrons, it is assumed here that SEI growth occurs at the interface between the SEI layer and the electrolyte, that is, toward the electrolyte. Then, the growth rate is limited by the transport of electrons through the SEI layer. The limiting current density can be calculated by the equation as shown below:

[0174]

[0175] Where D e_SEI·F is the diffusion coefficient of electrons in the SEI phase, which can be calculated by the following formula:

[0176]

[0177] By using this Arrhenius formula, the effect of temperature can be integrated into the SEI for recrystallization kinetics and then the final formation rate of the SEI can be calculated:

[0178]

[0179] Among them, i form，SEI is the SEI film growth rate; i F，SEI is the Faraday constant for the formation of SEI film; i lim It is the limiting current density caused by electron transport in the SEI layer;

[0180] Metal Li deposition: There is no free site required for Li insertion in metal Li deposition, and the formation rate of metal Li can also be calculated by the cathode Tafel equation:

[0181]

[0182] Among them, K Li Here is the rate constant, and it is also corrected by the Arrhenius formula:

[0183]

[0184] Among them, E a，Li is the activation energy of the lithium plating reaction rate constant.

[0185] S500: Solve the coupling model, the battery voltage, temperature distribution and capacity attenuation performance parameters, compare with the actual data, and verify the accuracy of aging prediction.

[0186] S501: The coupling model is solved, and the performance parameters of the battery's voltage, temperature distribution, and capacity decay are compared with the realized data to verify the accuracy of aging prediction; all three electrochemical reactions mentioned above occur in parallel and simultaneously on the surface of the graphite particles, competing for Li in the system. Assuming that SEI formation and Li deposition occur only during charging, the consumption of cyclable Li caused by side reactions will lead to battery capacity decay, and the formed SEI layer increases the potential drop on the electrode interface, both of which will lead to battery aging.

[0187] Furthermore, this embodiment also provides a three-dimensional lithium battery electrothermal coupling computer aging analysis system, including:

[0188] Building modules to establish a three-dimensional electrochemical model, the diffusion of lithium ions in the solid and liquid phases, the movement of electrons in the solid and liquid phases, and the calculation of battery temperature through heat dissipation and heat generation;

[0189] Calculation module, establishes a two-dimensional axisymmetric heat conduction model and the temperature distribution of cylindrical batteries;

[0190] A coupling module couples the three-dimensional electrochemical model with the two-dimensional thermal model to obtain a coupling model, wherein the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the thermal model is used as the input of the three-dimensional electrochemical model;

[0191] Simulation module, which simulates the battery aging process, including the consideration of SEI film formation reaction and metal lithium deposition reaction;

[0192] The verification module solves the coupling model, the battery's voltage, temperature distribution and capacity attenuation performance parameters, and compares them with the realized data to verify the accuracy of aging prediction.

[0193] This embodiment also provides a computer device, which is suitable for the three-dimensional lithium battery electrothermal coupling computer aging analysis method, including a memory and a processor; the memory is used to store computer executable instructions, and the processor is used to execute computer executable instructions to implement the three-dimensional lithium battery electrothermal coupling computer aging analysis method proposed in the above embodiment.

[0194] The computer device may be a terminal, and the computer device includes a processor, a memory, a communication interface, a display screen and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. The display screen of the computer device may be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device may be a touch layer covering the display screen, or a key, trackball or touchpad provided on the housing of the computer device, or an external keyboard, touchpad or mouse, etc.

[0195] This embodiment also provides a storage medium on which a computer program is stored. When the program is executed by a processor, the three-dimensional lithium battery electrothermal coupling computer aging analysis method proposed in the above embodiment is implemented.

[0196] In summary, compared with the widely used P2D model of lithium-ion batteries, this model has significantly better fitting results for experimental data in terms of discharge voltage and surface temperature, and can reproduce battery aging data. The three-dimensional electrochemical model is coupled with the two-dimensional thermal model. The model takes into account the aging behavior caused by the formation of SEI film on the surface of graphite particles and the plating of metal lithium, so the model is more accurate. The influence of SEI film and metal Li deposition on the model is taken into account.

[0197] The coupling of the 3D electrochemical model and the 2D thermal model brings unexpected synergistic effects. This coupling not only improves the simulation accuracy, but more importantly reveals the complex electrochemical-thermodynamic interactions within the battery. For example, the model predicts that under certain operating conditions, a local temperature increase may lead to a temporary improvement in battery performance, a phenomenon that is difficult to detect in traditional single models.

[0198] By considering the aging simulation of SEI film formation and metal lithium deposition, combined with a three-dimensional electrochemical-thermal coupling model, an unexpected "self-repair" mechanism inside the battery was discovered. The model predicts that under specific charge and discharge strategies, the SEI film in certain areas may dissolve and reform periodically, and this process may help maintain the long-term performance stability of the battery. This discovery provides a new idea for the development of new "self-healing" battery materials and the optimization of charging algorithms.

[0199] The coupled model predicts a non-intuitive temperature distribution pattern when simulating high-rate charge and discharge. Under certain conditions, multiple alternating hot and cold regions may form inside the battery, rather than a simple temperature gradient from the center to the surface. This discovery challenges traditional battery cooling design concepts and may lead to a revolutionary new thermal management system that significantly improves fast charging efficiency and safety.

[0200] By integrating the aging model with the electrochemical-thermal coupling model, a nonlinear relationship between battery capacity decay and temperature distribution was unexpectedly discovered. The model predicts that at certain stages of the battery life cycle, slightly uneven temperature distribution may slow down the overall capacity decay rate. This discovery overturns the traditional concept of "uniform cooling is best" and provides a new optimization direction for extending battery life.

[0201] When simulating battery performance under extreme temperature conditions, the coupled model predicted an unexpected "thermal activation" phenomenon. Under certain low-temperature conditions, short-term local heating may significantly improve the overall performance and life of the battery. This discovery provides innovative ideas for the development of new cold start strategies and polar batteries.

[0202] The coupled model found in long-term cycle simulations that stable "electrochemical channels" may form inside the battery, and the ion conductivity of these channels improves over time. This phenomenon explains why the performance of some batteries improves after initial use, and opens up a new direction for the design of new "aging-activated" batteries.

[0203] When simulating large battery packs, the coupled model predicts a group effect: properly designed battery pack arrangements may produce beneficial thermoelectric synergy effects, making the overall performance exceed the simple addition of individual batteries. This finding provides a new perspective for the optimal design of large-scale energy storage systems.

[0204] Example 2

[0205] Reference Figure 1 - Figure 2 , which is the second embodiment of the present invention, provides a three-dimensional lithium battery electrothermal coupling computer aging analysis method. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0206] In order to verify the effectiveness of the three-dimensional lithium battery electrothermal coupling computer aging analysis method proposed in the present invention, a common 18650 cylindrical lithium-ion battery on the market was selected for testing. The rated capacity of the battery is 3000mAh and the rated voltage is 3.7V. First, the battery was disassembled and analyzed, and the geometric dimensions and physical parameters of each component such as the electrode, diaphragm, and current collector were measured and recorded. Then, a three-dimensional electrochemical model was constructed according to the method of the present invention, including three parts: mass conservation, charge conservation, and energy conservation. In the mass conservation part, Fick's second law in the spherical coordinate system is used to describe the diffusion process of lithium ions in the solid phase, and the boundary conditions of the center and surface of the particle are considered; in the liquid phase, based on the concentrated electrolyte theory, the influence of diffusion and migration on the lithium ion concentration is considered. In the charge conservation part, combined with Ohm's law and Faraday's law of electrolysis, the relationship equations between the potential and the current in the solid phase and the liquid phase are established respectively. In the energy conservation part, three main heat sources, ohmic heat, activation polarization heat, and reaction heat, are considered, and a complete heat balance equation is established.

[0207] Next, a two-dimensional axisymmetric heat conduction model was constructed to more accurately describe the temperature distribution of cylindrical batteries. The model takes into account the different thermal properties of the battery's steel casing, nylon core, and rolled active electrode domain, and assumes that the scroll structure has anisotropic thermal conductivity. Then, the three-dimensional electrochemical model is coupled with the two-dimensional thermal model to form a complete coupled model. On this basis, two key aging mechanisms, SEI film formation and metallic lithium deposition, are further considered. The SEI film formation process is described by the cathode Tafel equation, and the Arrhenius equation is introduced to simulate the effect of temperature on the reaction rate. The cathode Tafel equation is also used for metallic lithium deposition, and the temperature dependence is considered.

[0208] In order to verify the accuracy and predictive ability of the model, a series of charge and discharge experiments were designed. First, constant current charge and discharge tests were carried out at 0.5C, 1C and 2C rates, and 50 cycles were performed at each rate. Then, low temperature performance tests were carried out in the temperature range of 0-40℃, and 1C rate charge and discharge were performed at intervals of 10℃. Finally, a long-term cycle life test was carried out, and 1000 cycles were performed at 1C rate at room temperature. During the entire test process, a high-precision battery test system was used to record voltage and current data, and an infrared thermal imager was used to monitor the battery surface temperature distribution in real time.

[0209] The experimental data are compared with the simulation results of the method of the present invention, and the results are shown in the following table:

[0210]

[0211] By comparing and analyzing the above data, we can draw the following conclusions:

[0212] In terms of discharge capacity prediction, the method of the present invention has a significant improvement over the traditional P2D model. Taking 1C discharge as an example, the experimentally measured capacity is 2912mAh, and the traditional model predicts 2968mAh with an error of 56mAh; while the method of the present invention predicts 2923mAh with an error of only 11mAh, and the prediction accuracy is improved by 80.4%. This improvement is reflected at different rates, indicating that the method of the present invention can more accurately simulate the behavior of the battery at different current densities.

[0213] In terms of temperature prediction, the advantages of the method of the present invention are more obvious. Taking the highest surface temperature during 2C discharge as an example, the experimentally measured temperature is 42.3°C, the traditional model predicts 39.5°C, and the error is 2.8°C; while the method of the present invention predicts 41.9°C, with an error of only 0.4°C, and the prediction accuracy is improved by 85.7%. This result fully demonstrates the importance of coupling the three-dimensional electrochemical model with the two-dimensional thermal model, which can more accurately describe the heat distribution and transfer process inside the battery.

[0214] The method of the present invention also performs well in predicting low-temperature performance. When 1C discharge is performed at 0°C, the experimentally measured capacity retention rate is 78.5%, while the traditional model predicts 82.3%, with an error of 3.8 percentage points; while the method of the present invention predicts 79.2%, with an error of only 0.7 percentage points, and the prediction accuracy is improved by 81.6%. This shows that the method of the present invention can better simulate the impact of temperature on battery performance and provide more reliable guidance for battery design and management in low-temperature application scenarios.

[0215] In terms of long-term cycle life prediction, the method of the present invention also shows obvious advantages. After 1,000 cycles, the experimentally measured capacity retention rate was 85.7%, while the traditional model predicted 89.2%, with an error of 3.5 percentage points; while the method of the present invention predicted 86.3%, with an error of only 0.6 percentage points, and the prediction accuracy was improved by 80.0%. This result proves that the method of the present invention can more accurately predict the long-term performance attenuation trend of the battery after considering aging mechanisms such as SEI film formation and metal lithium deposition.

[0216] It is worth noting that the prediction advantage of the method of the present invention is more obvious under high rate and extreme temperature conditions. This shows that the method has unique advantages in dealing with the complex electrochemical-thermal coupling process inside the battery, especially when the battery faces more severe working conditions. For example, under 2C discharge and 0℃ low temperature conditions, the prediction error of the method of the present invention is improved by more than 80%, which is of great significance for scenarios such as fast charging of electric vehicles and applications in cold regions.

[0217] By comparing the prediction results under different working conditions, it can also be found that the method of the present invention can capture some phenomena that are difficult to detect with traditional models. For example, during high-rate charge and discharge, the model predicts the non-uniform temperature distribution that may be formed inside the battery, which provides a new idea for optimizing the battery thermal management system. At the same time, in long-term cycle simulations, the model also predicts the "self-repair" phenomenon that may occur in battery performance, which provides valuable theoretical guidance for studying battery aging mechanisms and developing new battery materials.

[0218] In summary, the three-dimensional lithium battery electrothermal coupling computer aging analysis method proposed in the present invention has made significant progress in battery performance and life prediction by establishing a more comprehensive and accurate three-dimensional coupling model and taking into account key aging mechanisms. Compared with the traditional P2D model, this method has improved the prediction accuracy of various key indicators by more than 80%, especially in challenging scenarios such as high rates, extreme temperatures and long-term cycles. This high-precision prediction capability provides a reliable theoretical basis for battery design optimization, thermal management strategy improvement and service life extension, and is expected to promote the development of lithium-ion battery technology towards higher energy density, longer life and greater safety and reliability.

[0219] Through the above experiments, our inventors also provided a second simulation experiment for data comparison.

[0220] In order to verify the applicability of the three-dimensional lithium battery electrothermal coupling computer aging analysis method proposed in the present invention on different types of batteries, a new type of soft-pack power battery was selected for testing. The battery is a ternary lithium (NCM811) material system with a rated capacity of 100Ah and a rated voltage of 3.7V. First, the internal structure and material parameters of the battery were obtained in cooperation with battery manufacturers, including key parameters such as the particle size distribution of positive and negative active materials, electrolyte composition, and diaphragm porosity. Then, a three-dimensional electrochemical model was constructed according to the method of the present invention.

[0221] In the part of mass conservation, considering the characteristics of ternary materials, the modified Fick's law in spherical coordinates is used to describe the diffusion process of lithium ions in the solid phase, and the concentration-dependent diffusion coefficient is introduced; in the liquid phase, based on the modified concentrated electrolyte theory, the influence of lithium salt concentration in the electrolyte on the ion migration number is considered. In the part of charge conservation, the Butler-Volmer equation is used to describe the electrode reaction kinetics, and the influence of SEI film on the electrode surface on the reaction rate is considered. In the part of energy conservation, in addition to considering the conventional ohmic heat, activation polarization heat and reaction heat, the latent heat of phase change is also added to more accurately describe the phase change phenomenon that may occur during high-rate charge and discharge.

[0222] Next, a three-dimensional heat conduction model was constructed to adapt to the special structure of the soft-pack battery. The model takes into account the thermal properties of the battery's aluminum-plastic film shell, electrode stack structure, and tab connection area, and is solved using the finite element method. Then, the three-dimensional electrochemical model is fully coupled with the three-dimensional thermal model to form a complete multi-physics field coupling model. On this basis, the unique aging mechanisms of NCM materials are further considered, including structural collapse caused by excessive delithiation, manganese dissolution, crack propagation, etc. These mechanisms are reflected in the model through parameters such as the modified solid phase diffusion coefficient, effective reaction area, and interface impedance.

[0223] In order to fully verify the predictive ability of the model, a series of rigorous testing schemes were designed. First, constant current charge and discharge tests were carried out at 0.5C, 1C, 2C and 3C rates, with 100 cycles at each rate. Then, performance tests were carried out in the temperature range of -20°C to 55°C, with 1C rate charge and discharge at intervals of 15°C. Finally, an accelerated life test was carried out, with 2000 cycles at a 2C rate in a high temperature environment of 45°C. During the entire test process, a high-precision high-power battery test system was used to record voltage and current data, and a multi-point thermocouple array and infrared thermal imager were used to monitor the temperature distribution inside and outside the battery in real time.

[0224] The experimental data are compared with the simulation results of the method of the present invention, and the results are shown in the following table:

[0225]

[0226]

[0227] The method of the present invention performs well in predicting the capacity of large-capacity soft-pack batteries. Taking 2C discharge as an example, the experimentally measured capacity is 96.2Ah, the traditional model predicts 98.8Ah, with an error of 2.6Ah; while the method of the present invention predicts 96.5Ah, with an error of only 0.3Ah, and the prediction accuracy is improved by 88.5%. This significant improvement shows that the method of the present invention can more accurately describe the uneven reaction distribution inside large-size batteries.

[0228] In terms of internal temperature prediction, the advantages of the method of the present invention are more prominent. Taking the highest internal temperature during 3C discharge as an example, the experimentally measured temperature is 55.4°C, the traditional model predicts 50.8°C, and the error is 4.6°C; while the method of the present invention predicts 54.7°C, with an error of only 0.7°C, and the prediction accuracy is improved by 87.0%. This result fully demonstrates the superiority of the three-dimensional fully coupled model in dealing with complex heat conduction problems, especially under high-rate conditions.

[0229] The method of the present invention also performs well in predicting performance at extreme temperatures. When 1C discharge is performed at a low temperature of -20°C, the experimentally measured capacity retention rate is 65.3%, while the traditional model predicts 70.1%, with an error of 4.8 percentage points; while the method of the present invention predicts 66.0%, with an error of only 0.7 percentage points, and the prediction accuracy is improved by 83.3%. This shows that the method of the present invention can more accurately simulate the effect of temperature on the performance of battery materials and electrolytes.

[0230] In the accelerated aging test, the method of the present invention demonstrated a strong ability to predict long-term performance. After 2,000 high-temperature cycles, the experimentally measured capacity retention rate was 78.4%, while the traditional model predicted 82.9%, with an error of 4.5 percentage points; while the method of the present invention predicted 79.1%, with an error of only 0.7 percentage points, and the prediction accuracy was improved by 84.4%. It is particularly noteworthy that the method of the present invention performs better in predicting the rate of increase of internal resistance, with an improvement in prediction error of 84.1%, which is crucial for evaluating the power attenuation and thermal management requirements of the battery.

[0231] By comparing the prediction results under different working conditions, it is found that the method of the present invention can capture some complex phenomena that are difficult to identify with traditional models. For example, during high-rate charge and discharge, the model predicts the hot spot migration phenomenon that may occur inside the battery, which provides new ideas for optimizing the electrode structure and improving the current collection system. At the same time, in long-term cycle simulations, the model also predicts the possible phase change and structural evolution of NCM materials, which provides important clues for understanding the aging mechanism of ternary materials.

[0232] It is worth noting that the advantages of the method of the present invention in processing large-capacity soft-pack batteries show that it has unique value in solving the problem of battery amplification. Traditional models often have the problem of reduced accuracy when expanding from small-capacity batteries to large-capacity batteries, but the method of the present invention successfully overcomes this challenge by considering the three-dimensional structural effect and full coupling.

[0233] In summary, the three-dimensional lithium battery electrothermal coupling computer aging analysis method proposed in the present invention has once again demonstrated excellent performance in the application verification on large-capacity soft-pack power batteries. Compared with the traditional pseudo-two-dimensional model, this method has an improvement of more than 82% in the prediction accuracy of various key indicators, especially in challenging scenarios such as high rate, extreme temperature and long-term cycle. This high-precision prediction capability not only helps to optimize the existing battery design, but also provides a powerful tool for the development of the next generation of high energy density and long-life power batteries. By accurately simulating the behavior of batteries under various complex working conditions, this method is expected to promote the improvement of electric vehicle range, the development of fast charging technology and the further improvement of battery safety, providing solid technical support for the rapid development of the new energy vehicle industry.

[0234] 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 may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A three-dimensional lithium battery electrothermal coupling computer aging analysis method, characterized in that: include, Establish a three-dimensional electrochemical model to obtain the diffusion of lithium ions in the solid and liquid phases, the movement of electrons in the solid and liquid phases, and calculate the battery temperature through heat dissipation and heat generation; A two-dimensional axisymmetric heat conduction model was established to calculate the temperature distribution of cylindrical batteries; The three-dimensional electrochemical model is coupled with the two-dimensional thermal model to obtain a coupled model, the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the two-dimensional thermal model is used as the input of the three-dimensional electrochemical model; Simulate the battery aging process, including the SEI film formation reaction and the reaction of metal lithium deposition; Solve the coupling model to obtain the performance parameters of the battery's voltage, temperature distribution and capacity attenuation, and compare them with the actual data to verify the accuracy of aging prediction.

2. The three-dimensional lithium battery electrothermal coupling computer aging analysis method according to claim 1, characterized in that: The three-dimensional electrochemical model is established, including mass conservation, charge conservation and energy conservation. The diffusion of lithium ions in the solid phase and the liquid phase is obtained by mass conservation, the movement of electrons in the solid phase and the liquid phase is obtained by charge conservation, and the battery temperature is calculated by heat dissipation and heat generation by energy conservation. The mass conservation is obtained by the mass transfer of Li embedded in the active solid particles through Fick's second law using spherical coordinates, which uses the following expression: Where t is the time, r is the pseudo radial coordinate along the active spherical particle, Cs is the concentration of embedded Li in the solid phase, and Ds is the diffusion coefficient of embedded Li in the solid phase; Considering the boundary conditions at the center and surface of the particle, the boundary conditions can be easily obtained by the expression of the lithium ion concentration gradient at the center and boundary of the electrode particle according to Fick's first law, and the following expression can be used: Among them, j L is the diffusion flux of lithium ions, r is the pseudo-radial coordinate along the active spherical particle, Cs is the concentration of embedded Li in the solid phase, and Ds is the diffusion coefficient of embedded Li in the solid phase; The mass conservation of lithium ions in the liquid phase follows the concentrated electrolyte theory. Assuming that the electrolyte is a binary system, diffusion and migration can change the local lithium ion concentration, and the following expression is used: Among them, ε e represents the liquid volume fraction, C l is the Li ion concentration in the electrolyte; is the effective diffusion coefficient in the electrolyte, i l is the current density in the electrolyte; R source It is a source or sink of lithium ions caused by different reactions, including lithium insertion and deinsertion and side reactions involving lithium ions; Since there is no Li ion source or sink at the interface between the current collector and the active material, the corresponding boundary condition can be expressed as follows: Among them, C l is the Li ion concentration in the electrolyte; L neg is the thickness of the negative electrode, L sep is the diaphragm thickness; L pos is the thickness of the positive electrode; L neg -cc is the negative collector thickness.

3. The three-dimensional lithium battery electrothermal coupling computer aging analysis method according to claim 2, characterized in that: The three-dimensional electrochemical model is established, including mass conservation, charge conservation and energy conservation. The movement of electrons in the solid phase and the liquid phase is obtained by charge conservation. For the charge balance part, in the solid phase materials of the positive and negative electrodes, the relationship between the potential and the current can be obtained according to Ohm's law. The current is equal to the gradient of the negative potential multiplied by the conductivity, which is specifically expressed as follows: Among them, i s is the current density in the solid phase, is the effective conductivity in the solid phase; is the solid phase potential; At the same time, according to Faraday's law of electrolysis, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF. The change in solid-phase current can be related to the concentration of lithium ions participating in the electrode reaction. The specific relationship between the diffusion flux and the solid-phase transport current is as follows: ▽i s =-a s Fj L Among them, a s is the specific surface area, F is the Faraday constant; j L is the diffusion flux of lithium ions; Combining the above two expressions of Ohm's law of solid phase and Faraday's law of electrolysis, the relationship between solid phase potential and diffusion flux is as follows: Among them, a s is the specific surface area: is the solid phase potential; it represents the reaction area of ​​the electrode active material per unit volume; at the same time, the solid phase potential at the boundary with the negative electrode current collector is defined as 0. Since the diaphragm is composed of inert materials, only ions are allowed to pass through, while charges cannot pass through the diaphragm. Therefore, no charge passes through the interface between the two sides of the diaphragm and the solid. The following expression is used: in,, is the solid phase potential; is the liquid phase potential; is the effective conductivity of the solid phase; the charge flux at the junction of the current collector and the positive electrode is the current density of the battery I app , using the following expression: Among them, I app is the current density of the battery, is the liquid phase potential; is the effective conductivity of the solid phase; in the electrolyte, the charge balance is composed of Ohm's law and the migration potential, using the following expression: In the above formula, the second phase on the right side represents the effect of the lithium ion concentration in the liquid phase on the lithium ion concentration in the liquid phase, which represents the directional movement of lithium ions under concentration polarization, and the second phase on the right side represents the effect of the liquid phase potential on the lithium ion concentration, which conforms to the description of Ohm's law. Similarly, according to Faraday's law of electrolysis, that is, the reaction quantity is equal to the concentration of the substance participating in the reaction multiplied by its charge: Q = nzF, the change in liquid phase current is linked to the concentration of lithium ions participating in the electrode reaction, and finally the relationship between the diffusion flux and the liquid phase transport current is obtained as shown in the following equation: ▽(i l )=a s Fj L Finally, according to Ohm's law of liquid phase and Faraday's law of electrolysis, the relationship between diffusion flux and liquid phase current can be obtained as shown in the following formula: in, is the liquid effective conductivity, is the liquid phase potential; R is the thermodynamic constant; T is the temperature; F is the Faraday constant; C e is the liquid phase lithium ion concentration.

4. The three-dimensional lithium battery electrothermal coupling computer aging analysis method according to claim 3, characterized in that: The three-dimensional electrochemical model is established, including mass conservation, charge conservation and energy conservation. The battery temperature is calculated by heat dissipation and heat generation through energy conservation. During the operation of energy conservation, there are three different main heat sources in lithium-ion batteries: ohmic heat, activation polarization heat and reaction heat. The total energy conservation of the battery can be expressed as follows: Where, density; C p is the specific heat capacity of the battery; k T is the thermal conductivity; Q ohm is Ohmic heat, Q act is the activation polarization heat, Q react is the heat of reaction, ρ, C p , k T are the density, heat capacity and thermal conductivity of the materials in the corresponding computational domains, respectively; in this model, the outer container (steel), core (nylon) and active electrode domain (scroll) are considered; The scroll structure is assumed to be a homogeneous domain with anisotropic thermal conductivity, which can be calculated by lumped properties of different layers in parallel (kT,ang) or in series (kT,r); three different types of heat sources can be calculated as follows: Q act =a s Fj L the=a s I s (f s -f e -E ocv ) in, is the liquid phase potential; E o cv is the open circuit voltage or the potential at equilibrium; η is the overpotential of the electrode; The cooling condition applied to the external container surface is defined as: -k T,out ·▽T=h(T-T amb ) Among them, k T,out is the thermal conductivity of the external container, h is its heat transfer coefficient to the environment, and Tamb is the ambient temperature.

5. The three-dimensional lithium battery electrothermal coupling computer aging analysis method according to claim 4, characterized in that: The three-dimensional electrochemical model is coupled with the two-dimensional thermal model to obtain a coupled model, the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the two-dimensional thermal model is used as the input of the three-dimensional electrochemical model; The aging behavior caused by the formation of SEI film and metallic lithium plating on the surface of graphite particles is considered in the dimensional electrochemical model. In addition to the expected Li insertion and deinsertion, there are two reactions that consume cyclable Li, and it is assumed that these two reactions proceed along the electrochemical activity. Lithium insertion and deintercalation: The reaction rates of conventional intercalation and deintercalation reactions can be expressed using the Butler-Volmer equation as follows: Where n is the charge number of the ion; α a is the positive electrode transfer coefficient; α c is the negative electrode transfer coefficient; Among them, η represents the overpotential of the electrode, which is used to describe the change in potential caused by the embedding and migration of lithium ions in the electrode particles. Its expression is: h=φ s -f l -E ocv -Df s,film Among them, φ l is the liquid phase potential; Δφ s,film is caused by the surface resistance of the side reaction product film, where E ocv is the open circuit voltage or the potential at equilibrium.

6. The three-dimensional lithium battery electrothermal coupling computer aging analysis method according to claim 5, characterized in that: The simulation of the battery aging process includes considering the SEI film formation reaction and the metal lithium deposition reaction; SEI formation: Here, it is assumed that SEI formation is the electrochemical reduction of the electrolyte, and the following expression is used: S+Li + +e - →P SEI Where S is the electrolyte solvation reactant, P SEI It is a reduction product; The product is precipitated on the surface of the graphite particles to form a SEI layer; the reaction rate of SEI formation can be calculated according to the cathode Tafel equation, as shown in the following formula: Among them, K SEI is the reaction rate constant, is the lithium ion concentration on the surface of the electrode particles; C l , 0 is the initial lithium ion concentration in the liquid phase; Co (1-α) is the difference between the maximum lithium insertion concentration and the lithium ion concentration on the electrode surface; The Arrhenius equation was used to model the temperature-dependent kinetics: In addition, SEI formation is limited by the mass transport of substances through the SEI layer. Considering that the transport of electrolyte molecular substances is more difficult than the transport of electrons, it is assumed here that SEI growth occurs at the interface between the SEI layer and the electrolyte, that is, toward the electrolyte. Then, the growth rate is limited by the transport of electrons through the SEI layer. The limiting current density can be calculated by the equation as shown below: Where D e_SEI·F is the diffusion coefficient of electrons in the SEI phase, which can be calculated by the following formula: By using this Arrhenius formula, the effect of temperature can be integrated into the SEI for recrystallization kinetics and then the final formation rate of the SEI can be calculated: Among them, i form , SEI is the SEI film growth rate; i F , SEI is the Faraday constant for the formation of SEI film; i lim It is the limiting current density caused by electron transport in the SEI layer; Metal Li deposition: There is no free site required for Li insertion in metal Li deposition, and the formation rate of metal Li can also be calculated by the cathode Tafel equation: Among them, K Li Here is the rate constant, and it is also corrected by the Arrhenius equation: Among them, E a，Li is the activation energy of the lithium plating reaction rate constant.

7. The three-dimensional lithium battery electrothermal coupling computer aging analysis method according to claim 6, characterized in that: The solved coupling model is compared with the performance parameters of the battery's voltage, temperature distribution and capacity decay, and the aging prediction accuracy is verified. All three electrochemical reactions mentioned above occur in parallel and simultaneously on the surface of the graphite particles, competing for Li in the system. Assuming that SEI formation and Li deposition only occur during charging, the consumption of cyclable Li caused by side reactions will lead to battery capacity decay, and the formed SEI layer increases the potential drop on the electrode interface, both of which will lead to battery aging.

8. A three-dimensional lithium battery electrothermal coupling computer aging analysis system, based on the three-dimensional lithium battery electrothermal coupling computer aging analysis method according to any one of claims 1 to 7, characterized in that: Also includes, Building blocks to build three-dimensional electrochemical models, including the diffusion of lithium ions in solid and liquid phases, the movement of electrons in solid and liquid phases, and the calculation of battery temperature through heat dissipation and heat generation; The calculation module establishes a two-dimensional axisymmetric heat conduction model to calculate the temperature distribution of cylindrical batteries; A coupling module couples the three-dimensional electrochemical model with the two-dimensional thermal model to obtain a coupling model, wherein the heat calculated by the three-dimensional electrochemical model is used as the input of the two-dimensional thermal model, and the average temperature calculated by the thermal model is used as the input of the three-dimensional electrochemical model; Simulation module, which simulates the battery aging process, including the consideration of SEI film formation reaction and metal lithium deposition reaction; The verification module solves the coupling model to obtain the battery's voltage, temperature distribution and capacity attenuation performance parameters, and compares them with the actual data to verify the accuracy of aging prediction.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the three-dimensional lithium battery electrothermal coupling computer aging analysis method according to any one of claims 1 to 7 are implemented.

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 three-dimensional lithium battery electrothermal coupling computer aging analysis method according to any one of claims 1 to 7 are implemented.

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