Multi-physics field coupling modeling simulation method for puncture process of soft package lithium battery

Abstract

The invention belongs to the technical field of lithium ion battery modeling, and discloses a multi-physics field coupling modeling simulation method for a soft package lithium battery puncture process, which comprises the following steps: establishing a lithium ion battery electrochemical reaction model according to a P2D theory, and simulating an electrochemical phenomenon in a lithium ion battery discharge process by constructing a 1D battery model; current distribution in positive and negative current collectors is simulated by constructing a 2D current collector electron transmission model; heat production and heat transfer processes are simulated by constructing puncture 3D thermal models, and the models are coupled to form a comprehensive model. According to the multi-physical field coupling modeling simulation method for the puncture process of the soft package lithium battery, simulation research is carried out on SOC, voltage, current and temperature after puncture, an electrochemical-thermal coupling full 3D modeling method is adopted, the internal state of the soft package lithium battery is estimated, and the puncture precision of the soft package lithium battery is improved. And simulation support is provided for research on influence of external abuse on the battery and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery modeling, and in particular to a multi-physics field coupling modeling and simulation method for a soft-pack lithium battery puncture process. Background Art

[0002] Electric energy security is related to the overall national security. my country has made clear strategic deployments to accelerate the construction of a three-dimensional and efficient energy system to ensure safe, efficient and sustainable energy security in areas such as unmanned platforms and portable equipment. At present, there are many types of energy storage power sources used in unmanned platforms and portable equipment. Lithium batteries are widely used due to their excellent high specific energy characteristics. However, under various complex application conditions, lithium-ion batteries have the risk of thermal runaway causing fire and explosion. This has largely limited the large-scale application of lithium-ion batteries, and has restricted China's energy security capabilities and the development of a new generation of unmanned intelligent cluster technology.

[0003] In recent years, theoretical simulation has played an increasingly important role in the development of battery technology in response to the safety issues of lithium-ion batteries. Compared with experimental research, the advantages of theoretical simulation research are lower cost and shorter design verification cycle. The electrochemical-thermal coupling model is the most widely used model in recent years. It comprehensively considers the lithium concentration, current / potential distribution, energy conservation and electrochemical reaction process in the battery, and can simultaneously obtain the electrochemical process and temperature distribution in the battery, showing better predictability. Although the "electrochemical-thermal" coupling numerical calculation model helps to analyze the failure mechanism and thermal runaway mechanism of lithium-ion batteries, it does not substitute mechanical forces into the coupling numerical calculation model and cannot be used to study the dynamic response, failure mechanism and thermal runaway mechanism of lithium-ion batteries under impact. To this end, it is necessary to consider the development of a "mechanical-electrochemical-thermal" multi-field coupling numerical calculation model. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery, which is used to explore the self-discharge, temperature distribution cloud map and current density concentration of the soft-pack lithium-ion battery when an internal short circuit occurs after puncture, and to simulate the SOC, voltage, current and temperature after puncture; the present invention adopts an electrochemical-thermal coupling full 3D modeling method to estimate the internal state of the soft-pack lithium-ion battery, and provides simulation support for the study of the impact of external abuse on the battery.

[0005] To achieve the above object, the present invention provides a multi-physics field coupling modeling and simulation method for a soft-pack lithium battery puncture process, comprising the following steps:

[0006] Step S1, establishing a lithium-ion battery electrochemical reaction model according to the P2D theory, and simulating the electrochemical phenomena of the lithium-ion battery discharge process by constructing a 1D battery model;

[0007] Step S2, simulating the current distribution in the positive and negative current collectors by constructing a 2D current collector electron transport model;

[0008] Step S3: construct a puncture 3D thermal model to simulate the heat generation and heat transfer process, and couple these models to form a comprehensive model.

[0009] Preferably, the electrochemical reaction model of the lithium-ion battery is a two-dimensional model P2D which simplifies the battery geometry into a one-dimensional line segment, and the basic structure of the internal single layer includes three regions: the negative electrode, the diaphragm, and the positive electrode; wherein the pole piece structure parameters include: the thickness of the negative electrode, the thickness of the diaphragm, the thickness of the positive electrode, the lateral dimension between the positive and negative electrodes of the battery, the spherical coordinate radial dimension of the electrode active particles, the porosity of the pole piece, the volume fraction of each component and the electrode reaction surface area.

[0010] Preferably, the calculation domain of the 1D battery model includes the negative electrode coating, the diaphragm and the positive electrode coating; the left side of the negative electrode is set to be electrically grounded, that is, the electric potential is 0; the current density interface is set on the positive terminal side, and the current value is calculated in real time according to the battery voltage and the needle short-circuit resistance during the calculation process; when the voltage is 0, the current becomes 0.

[0011] Preferably, when the lithium-ion battery is connected to a load and discharged, the voltage between the positive and negative electrodes exceeds the equilibrium voltage, and the negative and positive electrodes undergo electrochemical reactions, which will cause the lithium ions Li + It escapes from the negative electrode active particles, reaches the positive electrode through the electrolyte and is embedded in the positive electrode active particles;

[0012] The Butler-Volmer equation for electrochemical reactions is used to calculate the reaction rate per unit area of ​​the electrode / electrolyte interface as follows:

[0013]

[0014] Among them, j Li is the electrochemical reaction current density, A / cm 2 ; i0 is the exchange current density of the electrode reaction in equilibrium state, A / cm 2 ; α a , α c are the conversion coefficients of the anode and cathode electrode reactions, respectively; R is the universal gas constant, 8.314 J / (mol·K 3 ); T is the thermodynamic temperature; η is the overpotential, V; F is the Faraday constant, 96487C / mol; φ s is the average solid phase potential, V; φ e is the average potential of the liquid phase, V; E eq is the equilibrium potential.

[0015] Preferably, lithium ion Li+ It is deintercalated from the surface of the active particles, so lithium ions Li appear inside the active particles. + concentration gradient;

[0016] In lithium ion + Driven by the concentration gradient, lithium ions Li + Diffusion in active particles is a solid phase diffusion process that follows Fick's second law as shown below:

[0017]

[0018] Where cs is the average volume concentration of lithium during solid phase diffusion, mol / cm 3 ; Ds is the diffusion coefficient of lithium in the solid phase diffusion process, cm 2 / S; r is the radius of the active material particle, cm; x is the lateral dimension between the positive and negative electrodes of the battery.

[0019] Preferably, when the lithium ion Li + After being released from the negative electrode active particles, the lithium ions Li in the electrolyte around the negative electrode plate + When the concentration of lithium ions Li + After being embedded in the positive electrode active particles, the lithium ions Li in the electrolyte around the positive electrode + Concentration decreases;

[0020] Driven by the concentration gradient, lithium ions Li + Diffusion from the negative electrode to the positive electrode, while the lithium ions Li + It will move under the influence of electromigration and convection factors, which is a liquid phase diffusion process, as shown below:

[0021]

[0022] Among them, ε e is the volume fraction of the liquid phase during diffusion; c e is the average volume concentration of lithium during liquid phase diffusion, mol / cm 3 ; is the diffusion coefficient of lithium in the liquid phase diffusion process, cm 2 / S; is the lithium ion migration number, 1.

[0023] Preferably, there is electron transfer and lithium ion Li on the current collector and the electrode. + The generation and absorption of , so the potential on the current collector and the electrode will change, that is, the solid phase potential process, as shown below:

[0024]

[0025] Among them, σeff is the solid phase conductivity of the electrode active material, S / cm.

[0026] Preferably, in the electrolyte, there are lithium ions Li + The diffusion, migration, convection, generation and absorption of electrolytes cause the potential of the electrolyte to change, which is the liquid phase potential process, as shown below:

[0027]

[0028] in, is the electrolyte conductivity, S / cm; is the lithium ion diffusion conductivity, S / cm;

[0029] Based on the above electrochemical P2D model principle, the electrochemical process equations of lithium-ion batteries are numerically solved.

[0030] Preferably, in step S2, a 2D current collector electron transport model is constructed to simulate the electron transport process in the current collector. According to the previous analysis, the positive and negative current collectors of the punctured part and the positive and negative current collectors of the unpunctured part are simulated respectively; the resistance and heat generation are analyzed by simulating the current formed by electron transport; the current and potential of the current collector are calculated based on Ohm's law; based on the potential results, the physical quantities of resistance, conductivity, electric field, current density and power loss are further calculated.

[0031] Preferably, in step S3, the 3D thermal model divides the battery into two parts, a punctured part and a non-punctured part;

[0032] First, the heat generated in the 1D battery model is loaded into the entire battery 3D thermal model structure, and the heat generated in the punctured and unpunctured 2D current collector electron transport models are loaded into the punctured part and unpunctured part of the 3D thermal model respectively;

[0033] Then, the ohmic heat is calculated based on the steel needle current and resistance calculated by the 1D battery model and the 2D current collector electron transport model, and loaded into the steel needle area of ​​the 3D thermal model;

[0034] Finally, the heat transfer in the battery 3D thermal model structure is calculated to obtain the battery temperature distribution.

[0035] Therefore, the present invention adopts the above-mentioned multi-physical field coupling modeling and simulation method of the puncture process of the soft-pack lithium battery to explore the self-discharge, temperature distribution cloud map and current density concentration of the soft-pack lithium-ion battery when an internal short circuit occurs after puncture, and simulates the SOC, voltage, current and temperature after puncture; the present invention adopts an electrochemical-thermal coupling full 3D modeling method to estimate the internal state of the soft-pack lithium-ion battery, and provides simulation support for the study of the impact of external abuse on the battery.

[0036] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of a multi-physics field coupling modeling and simulation method for a soft-pack lithium battery puncture process of the present invention;

[0038] Figure 2 is a 1D battery model of the present invention;

[0039] Figure 3 This is the electron transport model of the 2D current collector of the present invention; wherein (a) is the positive electrode current collector; (b) is the negative electrode current collector; (c) is the unpunctured current collector;

[0040] Figure 4 is the 3D thermal model of the present invention;

[0041] Figure 5 is a curve of voltage evolution during the discharge process in an embodiment of the present invention;

[0042] Figure 6 is the evolution of the SOC of the positive and negative electrodes of the battery during the acupuncture process in the embodiment of the present invention;

[0043] Figure 7 is the evolution of the voltage of the battery tab when acupuncture is performed in the embodiment of the present invention;

[0044] Figure 8 is the heat generated by the battery and the steel needle in the embodiment of the present invention;

[0045] Fig. 9 is the heat generation of the current collector tab in the embodiment of the present invention (the y coordinate is very small);

[0046] Fig.10 It is the evolution of the maximum temperature of the tab, battery and needle in the embodiment of the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0048] like Figure 1 As shown, the present invention provides a multi-physics field coupling modeling and simulation method for the soft-pack lithium battery puncture process, based on COMSOL Multiphysics software, using Comsol lithium-ion battery model, heat transfer module and current conservation module, to simulate and analyze the electrochemistry and heat of the puncture process, and simulate battery puncture under different conditions. The present invention establishes a triple numerical model, including the following steps:

[0049] Step S1, establishing a lithium-ion battery electrochemical reaction model according to the P2D theory, and simulating the electrochemical phenomena of the lithium-ion battery discharge process by constructing a 1D battery model.

[0050] The electrochemical reaction model of lithium-ion batteries is a two-dimensional model (P2D) that simplifies the battery geometry into a one-dimensional line segment. The basic structure of the internal single layer mainly includes three regions: the negative electrode, the separator, and the positive electrode. Specific pole piece structural parameters include: negative electrode thickness, separator thickness, positive electrode thickness, lateral dimension between the positive and negative electrodes of the battery, spherical coordinate radial dimension of the electrode active particles, pole piece porosity, volume fraction of each component and electrode reaction surface area.

[0051] 1D battery model such as Figure 2 As shown in the figure, the calculation domain includes the negative electrode coating, the separator and the positive electrode coating. The left side of the negative electrode is set to be electrically grounded, that is, the potential is 0, and the current density interface is set on the positive end. The current value is calculated in real time according to the battery voltage and the needle short-circuit resistance during the calculation process. When the voltage is 0, the current becomes 0.

[0052] When a lithium-ion battery is connected to a load for discharge, the equilibrium state in the open circuit condition is broken, the voltage between the positive and negative electrodes exceeds the equilibrium voltage, and electrochemical reactions occur at the negative and positive electrodes respectively, causing lithium ions to escape from the negative electrode active particles, reach the positive electrode through the electrolyte, and embed into the positive electrode active particles. The Butler-Volmer equation electrochemical reaction is used to calculate the reaction rate per unit area of ​​the electrode / electrolyte interface, as shown below:

[0053]

[0054] Among them, j Li is the electrochemical reaction current density, A / cm 2 ; i0 is the exchange current density of the electrode reaction in equilibrium state, A / cm 2 ; α a , α c are the conversion coefficients of the anode and cathode electrode reactions, respectively; R is the universal gas constant, 8.314 J / (mol·K 3 ); T is the thermodynamic temperature; η is the overpotential, V; F is the Faraday constant, 96487C / mol; φ s is the average solid phase potential, V; φ e is the average potential of the liquid phase, V; E eq is the equilibrium potential.

[0055] Lithium Ion + It is deintercalated from the surface of the active particle, so a lithium ion Li appears inside the active particle. + Driven by this concentration gradient, lithium ions Li +Diffusion in active particles, a process called solid-phase diffusion, follows Fick's second law as shown below:

[0056]

[0057] Where cs is the average volume concentration of lithium during solid phase diffusion, mol / cm 3 ; Ds is the diffusion coefficient of lithium in the solid phase diffusion process, cm 2 / S; r is the radius of the active material particle, cm; x is the lateral dimension between the positive and negative electrodes of the battery.

[0058] When lithium ion Li + After being released from the negative electrode active particles, the lithium ions Li in the electrolyte around the negative electrode plate + When the concentration of lithium ions Li + After being embedded in the positive electrode active particles, the lithium ions Li in the electrolyte around the positive electrode sheet + The concentration decreases, so there is a concentration gradient in the electrolyte inside the battery. Driven by this concentration gradient, the lithium ion Li + Diffusion from the negative electrode to the positive electrode, while the lithium ions Li + It will move under the influence of factors such as electromigration and convection. This process is called liquid phase diffusion process, as shown below:

[0059]

[0060] Among them, ε e is the volume fraction of the liquid phase during diffusion; c e is the average volume concentration of lithium during liquid phase diffusion, mol / cm 3 ; is the diffusion coefficient of lithium in the liquid phase diffusion process, cm 2 / S; is the lithium ion migration number, 1.

[0061] On the current collector and the electrode, there is electron transfer and lithium ion Li + The generation and absorption of , so the potential on the current collector and the electrode will change, this process is called the solid phase potential process, as shown below:

[0062]

[0063] Among them, σ eff is the solid phase conductivity of the electrode active material, S / cm.

[0064] In the electrolyte, there are lithium ions Li + The diffusion, migration, convection, generation and absorption of electrolytes will cause the potential of the electrolyte to change. This process is called the liquid phase potential process, as shown below:

[0065]

[0066] in, is the electrolyte conductivity, S / cm; is the lithium ion diffusion conductivity, S / cm.

[0067] Based on the above electrochemical P2D model theory, the electrochemical process equations of lithium-ion batteries are numerically solved.

[0068] Step S2: Simulate the current distribution in the positive and negative current collectors by constructing a 2D current collector electron transport model.

[0069] The 2D current collector electron transport model mainly simulates the electron transport process in the current collector. According to the previous analysis, the positive and negative current collectors of the punctured part and the positive and negative current collectors of the unpunctured part are simulated respectively. The mesh division and boundary conditions are as follows: Figure 3 As shown. By simulating the current formed by electron transfer, resistance and heat generation are effectively analyzed. The current and potential of the current collector are calculated based on Ohm's law. Based on the potential results, physical quantities such as resistance, conductivity, electric field, current density, and power loss are further calculated.

[0070] Step S3: construct a puncture 3D thermal model to simulate the heat generation and heat transfer process, and couple these models to form a comprehensive model.

[0071] like Figure 4 As shown, the 3D thermal model mainly divides the battery into two parts, the punctured part and the unpunctured part.

[0072] First, the heat generated in the 1D battery model is loaded into the entire battery 3D thermal model structure, and the heat generated in the punctured and unpunctured 2D current collector electron transport models are loaded into the punctured part and unpunctured part of the 3D thermal model, respectively.

[0073] Then, the ohmic heat is calculated based on the steel needle current and resistance calculated by the 1D battery model and the 2D current collector electron transport model and loaded into the steel needle area of ​​the 3D thermal model.

[0074] Finally, the heat transfer in the battery 3D thermal model structure is calculated to obtain the battery temperature distribution.

[0075] Example

[0076] This embodiment takes a 602040 lithium-ion battery as an example, and its parameters are shown in Table 1.

[0077] Table 1602040 Lithium Ion Battery Parameters

[0078]

[0079]

[0080] 1. Carry out charge and discharge simulation on the model constructed by the present invention, and compare and analyze with experimental data.

[0081] The voltage evolution curves of the battery during discharge at 200mA and 500mA are as follows: Figure 5 shown.

[0082] The mean absolute error and root mean square error are used to evaluate the accuracy of the model. The mean absolute error is the average of the absolute errors between the results of multiple measurements or calculations and the true value, as shown below:

[0083]

[0084] Among them, MAE represents the mean absolute error, X i represents the result of the i-th calculation, X t,i represents the value of the i-th measurement; n represents the number of measurements or calculations.

[0085] The root mean square error is the square root of the average of the sum of the squares of the absolute errors between the results of multiple measurements or calculations and the true value, as shown below:

[0086]

[0087] Among them, RMSE represents the root mean square error, X i represents the result of the i-th calculation, X t,i represents the value of the i-th measurement; n represents the number of measurements or calculations.

[0088] It is measured that the average absolute error is 0.0263V and the root mean square error is 4.20%.

[0089] 2. The algorithm is applied by taking the common situation that the steel needle punctures the battery completely and does not stay in the battery as an example.

[0090] At this time, the calculation needs to consider the 1D battery model, 2D current collector electron transport model and puncture 3D thermal model mentioned above. The residence time of the steel needle inside the battery is calculated according to the speed of the steel needle, and the internal short circuit process of the battery during this time is simplified. It is assumed that the steel needle passes through the battery and the battery no longer short-circuit occurs.

[0091] like Figure 6 As shown in the figure, the SOC evolution of the positive and negative electrodes of the battery during the acupuncture process, the self-discharge of the acupuncture short-circuited battery, and the lithium-ion Li + Transmitted from the negative electrode to the positive electrode. The negative electrode SOC decreases and the positive electrode SOC increases. Under this condition, the steel needle stays in the battery for a very short time, the short circuit time between the positive and negative electrodes is very low, and the SOC changes very little.

[0092] like Figure 7 As shown in the figure, the voltage evolution of the battery ear after needle puncture, the voltage of the short-circuited battery drops rapidly to below 0.8V, but after the steel needle penetrates the battery, the voltage rises rapidly to the battery open circuit voltage.

[0093] like Figure 8 and Fig. 9 The heat generation power shown in the figure, the so-called battery heat generation refers to the heat generated during the electrochemical reaction of the battery, and the heat generation of the current collector, the pole ear and the steel needle refers to the Joule heat generated when the current passes through. Since almost no current passes through the positive and negative pole ears, the heat generated by the pole ears is very small. In addition, the steel needle pierced all the electrode layers, each layer was short-circuited, and there was almost no current flowing between the layers. The current passing through the steel needle was also smaller than the case of piercing half of it. However, the battery short-circuit time is very short. After the steel needle penetrates the battery, the positive and negative electrodes are no longer short-circuited.

[0094] The maximum temperature evolution of the battery body, tabs and steel needles, such as Fig.10 As shown, the highest temperature occurs in the steel needle.

[0095] Therefore, the present invention adopts the above-mentioned multi-physical field coupling modeling and simulation method of the puncture process of the soft-pack lithium battery to explore the self-discharge, temperature distribution cloud map and current density concentration of the soft-pack lithium-ion battery when an internal short circuit occurs after puncture, and simulates the SOC, voltage, current and temperature after puncture; the present invention adopts an electrochemical-thermal coupling full 3D modeling method to estimate the internal state of the soft-pack lithium-ion battery, and provides simulation support for the study of the impact of external abuse on the battery.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution 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 they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery, characterized in that: The following steps are involved: Step S1, establishing a lithium-ion battery electrochemical reaction model according to the P2D theory, and simulating the electrochemical phenomena of the lithium-ion battery discharge process by constructing a 1D battery model; Step S2, simulating the current distribution in the positive and negative current collectors by constructing a 2D current collector electron transport model; Step S3: construct a puncture 3D thermal model to simulate the heat generation and heat transfer process, and couple these models to form a comprehensive model.

2. The multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery according to claim 1, characterized in that: The electrochemical reaction model of lithium-ion batteries is a two-dimensional model P2D, which simplifies the battery geometry into a one-dimensional line segment. The basic structure of the internal single layer includes three regions: negative electrode, separator, and positive electrode. Among them, the pole piece structure parameters include: negative electrode thickness, separator thickness, positive electrode thickness, lateral dimension between the positive and negative electrodes of the battery, spherical coordinate radial dimension of the electrode active particles, pole piece porosity, volume fraction of each component and electrode reaction surface area.

3. The multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery according to claim 1, characterized in that: The calculation domain of the 1D battery model includes the negative electrode coating, separator and positive electrode coating; the left side of the negative electrode is set to be electrically grounded, that is, the potential is 0; the current density interface is set on the positive terminal side, and the current value is calculated in real time according to the battery voltage and needle short-circuit resistance during the calculation process; when the voltage is 0, the current becomes 0.

4. The multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery according to claim 3, characterized in that: When a lithium-ion battery is connected to a load and discharged, the voltage between the positive and negative electrodes exceeds the equilibrium voltage, and electrochemical reactions occur at the negative and positive electrodes, respectively, which will cause the lithium ions Li + It escapes from the negative electrode active particles, reaches the positive electrode through the electrolyte and is embedded in the positive electrode active particles; The Butler-Volmer equation for electrochemical reactions is used to calculate the reaction rate per unit area of ​​the electrode / electrolyte interface as follows: h=φ s -f e -E eq Among them, j Li is the electrochemical reaction current density, A / cm 2 ; i0 is the exchange current density of the electrode reaction in equilibrium state, A / cm 2 ; α a , α c are the conversion coefficients of the anode and cathode electrode reactions, respectively; R is the universal gas constant, 8.314 J / (mol·K 3 ); T is the thermodynamic temperature; η is the overpotential, V; F is the Faraday constant, 96487C / mol; φ s is the average solid phase potential, V; φ e is the average potential of the liquid phase, V; E eq is the equilibrium potential.

5. The multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery according to claim 4, characterized in that: Lithium Ion + It is deintercalated from the surface of the active particles, so lithium ions Li appear inside the active particles. + concentration gradient; In lithium ion + Driven by the concentration gradient, lithium ions Li + Diffusion in active particles is a solid phase diffusion process that follows Fick's second law as shown below: Where cs is the average volume concentration of lithium during solid phase diffusion, mol / cm 3 ; Ds is the diffusion coefficient of lithium in the solid phase diffusion process, cm 2 / S; r is the radius of the active material particle, cm; x is the lateral dimension between the positive and negative electrodes of the battery.

6. The multi-physics field coupling modeling and simulation method for the soft-pack lithium battery puncture process according to claim 5, characterized in that: When lithium ion Li + After being released from the negative electrode active particles, the lithium ions Li in the electrolyte around the negative electrode plate + When the concentration of lithium ions Li + After being embedded in the positive electrode active particles, the lithium ions Li in the electrolyte around the positive electrode + Concentration decreases; Driven by the concentration gradient, lithium ions Li + Diffusion from the negative electrode to the positive electrode, while the lithium ions Li + It will move under the influence of electromigration and convection factors, which is a liquid phase diffusion process, as shown below: Among them, ε e is the volume fraction of the liquid phase during diffusion; c e is the average volume concentration of lithium during liquid phase diffusion, mol / cm 3 ; is the diffusion coefficient of lithium in the liquid phase diffusion process, cm 2 / S; is the lithium ion migration number, 1.

7. The multi-physics field coupling modeling and simulation method for the soft-pack lithium battery puncture process according to claim 6, characterized in that: On the current collector and the electrode, there is electron transfer and lithium ion Li + The generation and absorption of , so the potential on the current collector and the electrode will change, that is, the solid phase potential process, as shown below: Among them, σ eff is the solid phase conductivity of the electrode active material, S / cm.

8. The multi-physics field coupling modeling and simulation method for the puncture process of a soft-pack lithium battery according to claim 7, characterized in that: In the electrolyte, there are lithium ions Li + The diffusion, migration, convection, generation and absorption of electrolytes cause the potential of the electrolyte to change, which is the liquid phase potential process, as shown below: in, is the electrolyte conductivity, S / cm; is the lithium ion diffusion conductivity, S / cm; Based on the above electrochemical P2D model principle, the electrochemical process equations of lithium-ion batteries are numerically solved.

9. The multi-physics field coupling modeling and simulation method for the soft-pack lithium battery puncture process according to claim 1, characterized in that: In step S2, the electron transfer process in the current collector is simulated by constructing a 2D current collector electron transfer model. According to the previous analysis, the positive and negative current collectors of the punctured part and the positive and negative current collectors of the unpunctured part are simulated respectively; the resistance and heat generation are analyzed by simulating the current formed by electron transfer; the current and potential of the current collector are calculated based on Ohm's law; based on the potential results, the physical quantities of resistance, conductivity, electric field, current density and power loss are further calculated.

10. The multi-physics field coupling modeling and simulation method for the soft-pack lithium battery puncture process according to claim 1, characterized in that: In step S3, the 3D thermal model divides the battery into two parts, a punctured part and a non-punctured part; First, the heat generated in the 1D battery model is loaded into the entire battery 3D thermal model structure, and the heat generated in the punctured and unpunctured 2D current collector electron transport models are loaded into the punctured part and unpunctured part of the 3D thermal model respectively; Then, the ohmic heat is calculated based on the steel needle current and resistance calculated by the 1D battery model and the 2D current collector electron transport model, and loaded into the steel needle area of ​​the 3D thermal model; Finally, the heat transfer in the battery 3D thermal model structure is calculated to obtain the battery temperature distribution.

Images