Lithium battery electrochemical-thermal coupling model modeling method

Abstract

The invention provides a modeling method for an electrochemical-thermal coupling model of a lithium battery. The modeling method comprises the following steps: firstly, acquiring parameters required by modeling and accurately measuring electrochemical parameters such as an entropy thermal coefficient of a carbon fluoride material; then, based on an irreversible electrode conversion reaction theory, an electrochemical control equation of the carbon fluoride positive electrode is self-defined, and a coupling relation between the carbon fluoride concentration and a current source item is established, so that the construction of an electrochemical model is realized. And combining the electrochemical model with the heat transfer equation to establish an electrochemical-thermal coupling model of the lithium / carbon fluoride battery. In the modeling process, electrochemical information and a thermal characteristic curve obtained through experiments are used as reference objects, parameter optimization and calculation are carried out on an electrochemical model and an electrochemical-thermal coupling model in sequence, and after a simulation result is compared with a measured value, it is shown that the reliability of the model is high; furthermore, the electrochemical behavior and the thermal characteristic of the lithium / carbon fluoride battery can be efficiently and accurately predicted, and prediction and guidance are provided for thermal design and thermal management of a battery system.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a method for modeling an electrochemical-thermal coupling model of a lithium battery. Background Art

[0002] The lithium / carbon fluoride battery is currently the lithium primary battery with the highest theoretical specific energy in the world, and has the advantages of stable working voltage, wide working temperature range, long storage life, etc., and is widely used in high-end civilian instruments, medical equipment, military equipment, and aerospace and other cutting-edge scientific and technological fields. However, due to the poor electrical conductivity and kinetic performance of the carbon fluoride material, the polarization is serious and the thermal effect is significant during the battery discharge process, and its high heat generation characteristics may pose a threat to the use safety of the battery. Therefore, it is particularly important to predict the temperature change of the battery.

[0003] However, measuring the heat generation of the lithium / carbon fluoride battery through experiments is not only time-consuming and costly, but also unable to analyze the thermal behavior inside the battery. If the numerical simulation method is used, the number of experiments can be greatly reduced, and the simulation prediction of the battery thermal characteristics can be realized efficiently and accurately. For the numerical simulation of the lithium / carbon fluoride battery, the difficulty lies in that the working mechanism of this battery is very different from that of the lithium-ion battery. The lithium-ion battery is an intercalation reversible reaction, and its intercalation chemistry is a single-electron reaction. While the lithium / carbon fluoride battery is an irreversible electrode conversion reaction, and chemical bonds are broken and formed during the lithium ion insertion process in the carbon fluoride positive electrode. Its electrochemical conversion reaction is a new type of lithium storage mechanism different from the traditional lithium ion insertion / extraction reaction. Therefore, the traditional quasi-two-dimensional (Pseudo-Two-Dimensions, P2D) electrochemical model of the lithium-ion battery is not applicable to the lithium / carbon fluoride battery, and there is an urgent need to develop an electrochemical-thermal coupling model modeling method based on the irreversible electrode conversion reaction theory of the lithium / carbon fluoride battery to simulate the mass transfer, electrochemical kinetics, heat release, etc. that occur during the battery discharge process, and accurately predict the electrochemical characteristics and thermal behavior of the battery. Summary of the Invention

[0004] The purpose of the present invention is to provide, in view of the deficiencies of the prior art, a method for modeling an electrochemical-thermal coupling model of a lithium battery to accurately predict the electrochemical behavior and thermal characteristics of the battery, and provide prediction and guidance for the thermal design and thermal management of the battery system.

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

[0006] The embodiment of the present invention provides a method for modeling an electrochemical-thermal coupling model of a lithium battery, and the method includes:

[0007] Step 1: Obtain the geometric dimensions, material thermophysical property parameters required for building the model, and electrochemical parameters such as the entropy heat coefficient of the carbon fluoride material.

[0008] Step 2: Set the first physical field of the electrochemical model: Under the sub-nodes of the electrode surface in the first physical field, describe the electrochemical behavior of lithium metal based on the negative electrode kinetics; under the sub-nodes of the porous electrode, describe the electrochemical behavior of the positive electrode based on the electrochemical control equation of the carbon fluoride positive electrode; then input the corresponding electrochemical parameters of the material, and set the initial values and boundary conditions;

[0009] Step 3: Introduce and set the second physical field in the positive electrode domain, which is used to model the change in the concentration of carbon fluoride in the positive electrode, so that the concentration of carbon fluoride in the positive electrode electrochemical control equation in the first physical field is associated with the current source term, and a first one-dimensional electrochemical model is obtained;

[0010] Step 4: Construct an inverse problem model to optimize the parameters of the carbon fluoride reference concentration and the carbon fluoride positive electrode conductivity in the first one-dimensional electrochemical model, and obtain a second one-dimensional electrochemical model;

[0011] Step 5: Add the third physical field and set the corresponding initial values and boundary conditions to construct a three-dimensional thermal model of the lithium / carbon fluoride battery, and couple the thermal power of the second one-dimensional electrochemical model and the average temperature of the three-dimensional thermal model bidirectionally to obtain a first electrochemical-thermal coupling model;

[0012] Step 6: Construct an inverse problem model to optimize the parameter of the entropy heat coefficient of the carbon fluoride material in the first electrochemical-thermal coupling model, and obtain a second electrochemical-thermal coupling model;

[0013] Step 7: Based on the second electrochemical-thermal coupling model, predict the electrochemical characteristics and thermal behavior of the lithium / carbon fluoride battery under different working conditions.

[0014] Preferably, the entropy heat coefficient of the carbon fluoride material described in Step 1 is a key factor affecting the temperature rise change of the lithium / carbon fluoride battery, and this coefficient changes continuously with the depth of discharge, and needs to be accurately measured through experiments to improve the accuracy of the thermal model.

[0015] Preferably, the first physical field described in Step 2 is the electrochemical field of the lithium / carbon fluoride battery. The specific kinetic expression adopted by the lithium metal negative electrode in this physical field is:

[0016]

[0017] where: j loc，neg is the local current density of the negative electrode, j o，ref is the reference exchange current density of the negative electrode, E eq，neg is the equilibrium potential of the negative electrode, is the solid-phase electric potential, is the liquid-phase electric potential, F is the Faraday constant, C l is the electrolyte concentration, C l，ref is the reference concentration of the electrolyte, αa is the anodic transfer coefficient, α C is the cathodic transfer coefficient, and T is the temperature.

[0018] Preferably, based on the irreversible electrode conversion reaction theory of the lithium / carbon fluoride battery in step 2, an electrochemical control equation for the carbon fluoride positive electrode is customized. The specific electrochemical control equation adopted for the electrochemical behavior of the positive electrode is as follows:

[0019]

[0020] In the formula: j loc，pos is the local current density, j 0，pos is the exchange current density, α C is the cathodic transfer coefficient. c Li is the Li+ concentration, c Li，ref is the Li+ ion reference concentration, C CF is the carbon fluoride concentration, C CF，ref is the carbon fluoride reference concentration.

[0021] Preferably, the first one-dimensional electrochemical model in step 3 is an unoptimized one-dimensional electrochemical model of the lithium / carbon fluoride battery.

[0022] Preferably, the second physical field in step 3 is an ordinary differential equation field introduced in the positive electrode domain, which is used to model the change in the concentration of carbon fluoride in the positive electrode and establish a connection between the carbon fluoride concentration and the current source term in the electrochemical control equation in step 2. The specific equation is as follows:

[0023]

[0024]

[0025] In the formula: d a is the damping coefficient, f is the source term, a is the specific surface area of activity, C CF is the carbon fluoride concentration, F is the Faraday constant, V i is the stoichiometric coefficient, and n is the number of electrons participating in the electrochemical reaction.

[0026] Preferably, the second one-dimensional electrochemical model in step 4 is an optimized one-dimensional electrochemical model of the lithium / carbon fluoride battery.

[0027] Preferably, the parameter optimization of the total concentration of the positive carbon fluoride reaction and the conductivity of the carbon fluoride positive electrode in step 4 is specifically as follows: Compare the battery discharge curves obtained from experiments and simulations respectively, and use the mean square error value between the curves as the objective function to form an inverse problem model. Given the initial parameter values and intervals, select an optimization algorithm for multi-parameter identification to adjust the above parameter estimation values, and preset the first optimization tolerance. After multiple iterations, make the simulation results of the battery discharge curve meet the set requirements with the experimental test results, and obtain the second one-dimensional electrochemical model.

[0028] Preferably, the first electrochemical-thermal coupling model in step 5 is the unoptimized electrochemical-thermal coupling model of the lithium / carbon fluoride battery.

[0029] Preferably, for the electrochemical-thermal coupling in step 5, the volume-averaged thermal power of the second one-dimensional electrochemical model is added to the three-dimensional thermal model as the heat source, and the average temperature of the three-dimensional thermal model is used as the reaction temperature of the one-dimensional electrochemical model, so as to realize the bidirectional coupling of one-dimensional electrochemistry and three-dimensional heat.

[0030] Preferably, the second electrochemical-thermal coupling model in step 6 is the optimized electrochemical-thermal coupling model of the lithium / carbon fluoride battery.

[0031] Preferably, for the construction of the inverse problem model in step 6 to optimize the entropy heat coefficient of the carbon fluoride material in the first lithium / carbon fluoride battery electrochemical-thermal coupling model, specifically, first fit the entropy heat coefficients of carbon fluoride at different discharge depths into polynomials, and set the constants in the polynomials as undetermined parameters. Compare the battery temperature rise curves obtained from experiments and simulations respectively, and use the mean square error value between the curves as the objective function to form an inverse problem model. Select an optimization algorithm for multi-parameter identification to adjust the above undetermined parameters, and preset the second optimization tolerance. After multiple iterations, make the simulation results of the battery temperature rise meet the set requirements with the experimental test results, and obtain the second lithium / carbon fluoride battery electrochemical-thermal coupling model.

[0032] The present invention provides a method for modeling an electrochemical-thermal coupling model of a lithium battery. First, the parameters required for modeling a lithium / carbon monofluoride battery are obtained, and the electrochemical parameters such as the entropy heat coefficient of the carbon monofluoride material are accurately measured. Then, based on the theory of irreversible electrode conversion reaction, the electrochemical control equation of the carbon monofluoride positive electrode is customized, and the coupling relationship between the carbon monofluoride concentration and the current source term is established, thereby realizing the construction of the electrochemical model. Then, by combining the electrochemical model with the heat transfer equation, an electrochemical-thermal coupling model of the lithium / carbon monofluoride battery is established. And during the modeling process, taking the electrochemical information and thermal characteristic curves obtained from experiments as the reference objects, the parameters of the electrochemical model and the electrochemical-thermal coupling model are optimized and calculated successively. After comparing the simulation results with the measured values, it shows that the model has high credibility. The present invention constructs an electrochemical-thermal coupling model applicable to lithium / carbon monofluoride batteries, which can efficiently and accurately predict the electrochemical behavior and thermal characteristics of lithium / carbon monofluoride batteries, providing prediction and guidance for the thermal design and thermal management of battery systems.

[0033] Compared with the prior art, it has the following beneficial effects:

[0034] Based on the theory of irreversible electrode conversion reaction and heat transfer theory, the present invention customizes the electrochemical control equation and ordinary differential equation of the carbon monofluoride positive electrode, constructs an electrochemical-thermal coupling model applicable to lithium / carbon monofluoride batteries, simulates the mass transfer, electrochemical kinetics, heat release, etc. occurring during the battery discharge process, clarifies the relationship between the battery discharge power, working time, heat generation power and temperature rise, and makes up for the gap in the electrochemical-thermal coupling numerical simulation technology of existing lithium / carbon monofluoride batteries.

[0035] Starting from the accurate measurement of electrochemical parameters and parameter identification, taking the electrochemical information obtained from experiments as the reference object, the present invention optimizes and calculates the parameters of the electrochemical model and the electrochemical-thermal coupling model successively. After comparing the simulation results with the measured values, it shows that the model has high credibility, realizes the efficient and accurate prediction of the electrochemical behavior and thermal characteristics of lithium / carbon monofluoride batteries, and provides prediction and guidance for the thermal design and thermal management of battery systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The following drawings are only intended to illustrate and explain the present invention, and do not limit the scope of the present invention.

[0037] Wherein:

[0038] Figure 1 : is a schematic diagram of the implementation process of the method for constructing an electrochemical-thermal coupling model of a lithium / carbon monofluoride battery in an embodiment of the present invention;

[0039] Figure 2 : is a flowchart of the inverse solution of one-dimensional electrochemical model parameters of a lithium / carbon monofluoride battery in a specific embodiment of the present invention;

[0040] Figure 3: Schematic diagram of the discharge curve of the lithium / carbon fluoride battery in a specific embodiment of the present invention;

[0041] Figure 4 : Schematic diagram of the three-dimensional geometric model of the lithium / carbon fluoride battery in a specific embodiment of the present invention;

[0042] Figure 5 : Flow chart for the inverse solution of the parameters of the electrochemical-thermal coupling model of the lithium / carbon fluoride battery in a specific embodiment of the present invention;

[0043] Figure 6 : Curve graph showing the change of the thermal power of the lithium / carbon fluoride battery with the discharge power and working time in a specific embodiment of the present invention;

[0044] Figure 7 : Curve graph of the discharge curve and temperature rise of the lithium / carbon fluoride battery in a specific embodiment of the present invention;

[0045] Figure 8 : Contour map of the temperature distribution of the single cell of the lithium / carbon fluoride battery in a specific embodiment of the present invention;

[0046] Figure 9 : Position and number of the temperature detection points of the single cell of the lithium / carbon fluoride battery in a specific embodiment of the present invention. Detailed implementation manner

[0047] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, terms such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0048] In this embodiment, a 5Ah lithium / carbon fluoride soft-pack battery is taken as an example, and a simulation model is constructed using commercial finite element software.

[0049] See Figure 1 , an embodiment of the present invention provides a method for constructing an electrochemical-thermal coupling model of a lithium / carbon fluoride battery, and the method includes:

[0050] Step 1: Obtain the parameters required for constructing the lithium / carbon fluoride battery model, including electrochemical parameters, thermophysical parameters, and geometric parameters;

[0051] Since there are many physical parameters involved in the description of the implementation process of the present invention. For the convenience of understanding the technical solution of the present invention, the physical parameters that may be used later are first presented in the form of a list. When each physical parameter appears later, it will not be explained separately one by one.

[0052] The battery design parameters required for building the model include electrochemical parameters, thermophysical parameters, and geometric parameters. The electrochemical parameters are shown in Table 1 (the specific electrochemical parameters of the positive electrode, negative electrode, and separator are subject to the measured data), the thermophysical parameters are shown in Table 2, and the one-dimensional and three-dimensional geometric parameters of the battery are shown in Table 3.

[0053]

[0054]

[0055] Table 1

[0056] Name Value Description kT_batt_x 17.634 W / (m·K) Thermal conductivity in the X direction kT_batt_y 0.86421 W / (m·K) Thermal conductivity in the Y direction kT_batt_z 17.634 W / (m·K) Thermal conductivity in the Z direction rho_batt <![CDATA[2317kg / m 3 > Battery density Cp_batt 1801.7 J / (kg·K) Battery heat capacity L_pos_cc <![CDATA[8×10 -6 m]]> Thickness of the positive current collector kT_pos 1.04 W / (m·K) Thermal conductivity of the positive electrode kT_neg 84.8 W / (m·K) Thermal conductivity of the negative electrode kT_pos_cc 170 W / (m·K) Thermal conductivity of the positive current collector kT_sep 0.344 W / (m·K) Thermal conductivity of the separator rho_pos <![CDATA[2750kg / m 3 > Positive electrode density rho_neg <![CDATA[534kg / m 3 > Negative electrode density rho_pos_cc <![CDATA[2770kg / m 3 > Positive current collector density rho_sep <![CDATA[920kg / m 3 > Separator density Cp_pos 1680 J / (kg·K) Specific heat capacity of the positive electrode Cp_neg 3580 J / (kg·K) Specific heat capacity of the negative electrode Cp_pos_cc 875 J / (kg·K) Specific heat capacity of the positive current collector Cp_sep 1978.2 J / (kg·K) Specific heat capacity of the separator

[0057] Table 2

[0058]

[0059]

[0060] Table 3

[0061] In addition, the entropy heat coefficient is a key factor affecting the battery temperature rise. In order to enable the model to accurately predict the heat generation of the lithium / carbon fluoride battery, it is also necessary to accurately measure the entropy heat coefficient of the carbon fluoride material. According to the Bernadia heat generation rate model, the heat generation rate q v of the battery can be obtained in relation to the entropy heat coefficient . The specific expression is as follows:

[0062]

[0063] where: q v is the heat generation rate per unit volume of the battery cell, E is the open-circuit voltage, I is the discharge current, and V is the volume of the battery cell.

[0064] In this embodiment, the entropy heat coefficient of the carbon fluoride material is measured based on the entropy heat coefficient test. The specific test steps are as follows:

[0065] (1) At room temperature, the lithium / carbon fluoride battery is left to stand for 1 h.

[0066] (2) At this moment, the state of charge of the battery is 100%. The battery is allowed to vary at 50 °C, 40 °C, 30 °C, 20 °C, and 10 °C. To ensure the stability of the open-circuit voltage of the battery at different temperatures, the standing times at different temperatures are 9 h, 3 h, 3 h, 3 h, and 3 h respectively, and the open-circuit voltage values are recorded.

[0067] (3) The thermostat is adjusted to 25 °C and maintained for 3 h, and the battery discharges 10% of its rated capacity.

[0068] (4) Repeat steps (2) and (3) 10 times to obtain the relationship between temperature and open circuit voltage of the battery with the state of charge ranging from 100% to 0%.

[0069] (5) Calculate the entropy heat coefficient values of the battery at different states of charge. According to the measured entropy heat coefficient values, fit the curve of the entropy heat coefficient varying with the depth of discharge.

[0070] To reduce the measurement error of the entropy heat coefficient, repeat the measurement of the entropy heat coefficient in different temperature ranges multiple times and take the average value to obtain the overall average entropy heat coefficient.

[0071] Step 2: According to the working principle of the lithium / carbon fluoride battery, construct the electrochemical equation of the lithium / carbon fluoride battery, set the first physical field of the lithium / carbon fluoride battery, then input the corresponding electrochemical parameters of the materials, and set the initial values and boundary conditions.

[0072] The first physical field is the electrochemical field of the lithium / carbon fluoride battery. Under the sub-node of the electrode surface in this physical field, describe the electrochemical behavior of lithium metal based on the negative electrode kinetics. The specific kinetic expression adopted for the lithium metal negative electrode of the battery is:

[0073]

[0074] In the formula: j loc，neg is the local current density of the negative electrode, j o，ref is the reference exchange current density of the negative electrode, E eq，neg is the equilibrium potential of the negative electrode, is the solid-phase electric potential, is the liquid-phase electric potential, F is the Faraday constant, C l is the electrolyte concentration, C l，ref is the reference concentration of the electrolyte, α a is the anodic transfer coefficient, α C is the cathodic transfer coefficient, T is the temperature.

[0075] Under the sub-node of the porous electrode in this physical field, customize the electrochemical control equation of the carbon fluoride positive electrode based on the irreversible electrode conversion reaction theory of the lithium / carbon fluoride battery. The specific electrochemical control equation is as follows:

[0076]

[0077] In the formula: j loc，pos is the local current density, j 0，pos is the exchange current density, α C is the cathodic transfer coefficient, c Li is Li + concentration, c Li，ref is Li + ion reference concentration, C CFis the concentration of carbon fluoride, C CF，ref is the reference concentration of carbon fluoride.

[0078] The input boundary conditions in this physical field include the initial electrolyte potential, initial electrolyte salt concentration, initial electric potential, and positive electrode current density in the positive electrode domain and the separator domain.

[0079] Step 3: Introduce and set a second physical field in the positive electrode domain. The second physical field is an ordinary differential equation field, which is used to describe the coupling relationship between the concentration of carbon fluoride and the current source term in the positive electrode electrochemical control equation. The specific ordinary differential equation is as follows:

[0080]

[0081]

[0082] In the formula: d a is the damping coefficient, f is the source term, a is the specific surface area of activity, C CF is the concentration of carbon fluoride, F is the Faraday constant, V i is the stoichiometric coefficient, and n is the number of electrons participating in the electrochemical reaction.

[0083] The input boundary conditions include the initial time derivative of the carbon fluoride concentration and the initial value of the carbon fluoride concentration.

[0084] Select a transient with initialization to study the electrochemical reaction process of the battery. Set the stop condition as the voltage at the positive electrode current collector end being less than 1.5 V, and calculate the preliminary simulation results. Thus, a first one-dimensional electrochemical model is obtained, which is the unoptimized one-dimensional electrochemical model of the lithium / carbon fluoride battery.

[0085] Step 4: Construct an inverse problem model to optimize the parameters of the reference concentration of carbon fluoride and the conductivity of the positive electrode of the carbon fluoride in the first one-dimensional electrochemical model, and obtain a second one-dimensional electrochemical model.

[0086] See Figure 2 , which is the flow chart for inverse calculation of the parameters of the one-dimensional electrochemical model of the lithium / carbon fluoride battery. For the inverse calculation of the parameters of the first one-dimensional electrochemical model, first combine the battery design parameters to give the initial values and value ranges of the parameters. By comparing the experimental battery discharge curve with the simulated battery discharge curve, the mean square error value between the curves is used as the objective function, thus constructing an inverse problem model (optimization model). Select an optimization algorithm for multi-parameter identification to update and adjust the parameter values, and set the first optimization tolerance to 0.01. After multiple iterations until convergence, make the simulated result of the battery discharge curve close to the experimental test result, and obtain a second one-dimensional electrochemical model, that is, obtain the optimized one-dimensional electrochemical model of the lithium / carbon fluoride battery. The specific definition method of the above optimization algorithm is as follows:

[0087]

[0088]

[0089] Among them, x 1 , x 2 is the parameter to be solved, j represents the number of sampling points in the iterative process, and i represents the number of stages. is the reference benchmark value of the j-th sampling point, is the simulation value of the j-th sampling point, u i is the weighting coefficient of the i-th stage, and Δf i is the mean square error value of the i-th stage.

[0090] See Figure 3 , which is the simulation result of the discharge curve of the lithium / carbon fluoride battery at different rates after the electrochemical model is optimized. It can be seen from the figure that under the premise of ensuring the calculation efficiency, the trend of the obtained discharge curve conforms to the actual situation, and the electrochemical performance of the battery can be predicted.

[0091] Step 5: Establish a three-dimensional geometric model of the battery, add a third physical field and set the corresponding initial values and boundary conditions, and then obtain a three-dimensional thermal model of the lithium / carbon fluoride battery after mesh generation.

[0092] See Figure 4 , which is the three-dimensional geometric model of the battery, consisting of three parts: the battery cell, the positive electrode tab, and the negative electrode tab. This geometric model is constructed based on the Cartesian coordinate system. The X-axis direction is the battery width direction, the Y-axis direction is the battery thickness direction, and the Z-axis direction is the battery length direction.

[0093] Due to the complexity of the reactions inside the battery, corresponding assumptions need to be made before establishing the thermal coupling model: assume that parameters such as the density, thermal conductivity, and specific heat capacity of the battery do not change with temperature and state of charge; ignore the convective and radiative heat transfer inside the battery.

[0094] The third physical field is the solid heat transfer field. The thermal model of the lithium / carbon fluoride battery is a homogenized anisotropic three-dimensional thermal finite element model built using the solid heat transfer interface in commercial finite element software. The heat dissipation condition of the thermal model is set as air convection heat dissipation, and the thermal power calculated by the second one-dimensional electrochemical model is added to the battery cell domain as a heat source through the average value operator, and then the temperature field T(x 1 , y 1 , z 1 , t) of the battery can be calculated. Then, T(x 1 , y 1 , z 1, the volume average value of the temperature field is obtained to get the distribution function of temperature varying with time, which is used as the reaction temperature of the second one-dimensional electrochemical model, and it affects the electrochemical reaction process in the model in real time to realize the bidirectional coupling of heat power - temperature between the one-dimensional electrochemical model and the three-dimensional thermal model. The thermal characteristic equation of the three-dimensional thermal model is as follows:

[0095]

[0096] In the formula: ρ is the density, C p is the constant-pressure heat capacity, q v is the heat generation rate per unit volume of the battery cell.

[0097] The model constructed in the above steps is the first electrochemical-thermal coupling model, that is, the unoptimized electrochemical-thermal coupling model of lithium / carbon monofluoride battery

[0098] Step 6: Optimize the parameters of the entropy heat coefficient of the carbon monofluoride material in the first electrochemical-thermal coupling model.

[0099] See Figure 5 , which is the flow chart for inverse calculation of the parameters of the electrochemical-thermal coupling model of lithium / carbon monofluoride battery. First, the entropy heat coefficients of carbon monofluoride at different discharge depths are fitted into a polynomial, and the constants in the polynomial are set as undetermined parameters. The mean square error value between the curves is used as the objective function by comparing the battery temperature rise curves obtained from experiments and simulations respectively, thus forming an inverse problem model. Select an optimization algorithm for parameter identification to update and adjust the above undetermined parameters, and preset the second optimization tolerance to 0.01. After multiple iterations until convergence, the battery temperature rise simulation results are close to the experimental test results, and the second electrochemical-thermal coupling model, that is, the optimized electrochemical-thermal coupling model of lithium / carbon monofluoride battery, is obtained.

[0100] See Figure 6 , which is the curve of the heat power of the battery varying with the discharge power and working time at 1C rate calculated by the above second electrochemical-thermal coupling model. The battery discharge power drops suddenly accompanied by a sharp increase in the battery heat generation power. At different working times, the battery heat generation power shows a trend of sharp increase - gentle - sharp increase. The relationship between the battery discharge power, working time and heat generation power is established.

[0101] See Figure 7 , which is the discharge curve of the battery at 1C rate and the temperature rise curve of the battery under this condition calculated by the above second electrochemical-thermal coupling model.

[0102] Step 7: Compare the simulation result data obtained from the second electrochemical-thermal coupling model with the test results of the lithium / carbon monofluoride battery reference sample. As shown in Table 4, the median voltage of the simulated and measured discharge curves is selected for comparison, and it can be seen that the simulation results are highly reliable after comparison; as shown in Table 5, the specific capacity ratio of the simulated and measured discharge curves is selected for comparison, and it can be seen that the simulation results are highly reliable after comparison.

[0103]

[0104] Table 4

[0105]

[0106] Table 5

[0107] See Figure 8 , which is the temperature distribution contour map of the battery at a 1C rate (heat generation at the tab is not considered in this model). As shown in Table 6, the maximum temperature of the simulated and measured battery is selected for comparison, and it can be seen that the simulation results are highly reliable after comparison.

[0108]

[0109] Table 6

[0110] See Figure 9 , which shows the positions and numbers of the temperature detection points of the battery cell. In the thermal model, the temperatures at five positions in the figure are extracted and averaged, and temperature sensors are also set at the corresponding positions on the battery reference sample to detect the temperature, and finally averaged. As shown in Table 7, at the end of the battery discharge, the average temperatures of the simulated and measured battery at the same positions are selected for comparison, and it can be seen that the simulation results are highly reliable after comparison.

[0111]

[0112] Table 7

[0113] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains are also able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions, or variations made by those skilled in the art based on the present invention fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A lithium battery electrochemical-thermal coupling model modeling method, characterized in that: The method comprises: Step 1: Obtain the geometric dimensions and material thermophysical parameters required to build a lithium / carbon fluoride battery model, and determine the entropy thermal coefficient of the carbon fluoride material; Step 2: Set the first physical field of the electrochemical model. Under the electrode surface subnode in the first physical field, describe the electrochemical behavior of lithium metal based on the negative electrode kinetics; under the porous electrode subnode, describe the electrochemical behavior of the positive electrode based on the electrochemical control equation of the carbon fluoride positive electrode; then input the corresponding electrochemical parameters of the material, set the initial value and boundary conditions; Step 3: Introduce and set a second physical field in the positive electrode domain to model the concentration change of carbon fluoride in the positive electrode, so that the carbon fluoride concentration in the positive electrode electrochemical control equation in the first physical field is associated with the current source term to obtain a first one-dimensional electrochemical model; Step 4: construct an inverse problem model, optimize the parameters of the carbon fluoride reference concentration and the carbon fluoride positive electrode conductivity in the first one-dimensional electrochemical model, and obtain a second one-dimensional electrochemical model; Step 5: Add a third physical field and set corresponding initial values ​​and boundary conditions to construct a three-dimensional thermal model of the lithium / carbon fluoride battery, and bidirectionally couple the thermal power of the second one-dimensional electrochemical model and the average temperature of the three-dimensional thermal model to obtain a first electrochemical-thermal coupling model; Step 6: construct an inverse problem model, optimize the entropy thermal coefficient of the carbon fluoride material in the first electrochemical-thermal coupling model, and obtain a second electrochemical-thermal coupling model; Step 7: Based on the second electrochemical-thermal coupling model, predict the electrochemical behavior and thermal characteristics of the lithium / carbon fluoride battery under different operating conditions.

2. A lithium battery electrochemical-thermal coupling modeling method according to claim 1, characterized in that: In step 2, the first physical field is a lithium / carbon fluoride battery electrochemical field, the first one-dimensional electrochemical model is an unoptimized lithium / carbon fluoride battery one-dimensional electrochemical model, and the kinetic expression used for the lithium metal negative electrode of the battery is: Where: j loc,neg is the local current density at the negative electrode, j o,ref is the negative electrode reference exchange current density, E eq,neg is the negative electrode equilibrium potential, is the solid phase potential, is the liquid phase potential, F is the Faraday constant, C l is the electrolyte concentration, C l,ref is the reference concentration of electrolyte, α a is the anode transfer coefficient, α C is the cathode transfer coefficient, and T is the temperature.

3. A lithium battery electrochemical-thermal coupling modeling method according to claim 1, characterized in that: In step 2, under the porous electrode subnode, the electrochemical control equation used by the battery carbon fluoride positive electrode is specifically: Where: j loc,pos is the local current density, j 0,pos is the exchange current density, α C is the cathode transfer coefficient; c Li For Li + Concentration, c Li,ref For Li + Ion reference concentration, C CF is the concentration of carbon fluoride, C CF,ref is the reference concentration of fluorinated carbon.

4. A lithium battery electrochemical-thermal coupling modeling method according to claim 1, characterized in that: In step 3, the second physical field is an ordinary differential equation field, which is used to model the concentration change of carbon fluoride in the positive electrode, so that the carbon fluoride concentration in the positive electrode electrochemical control equation in the first physical field is associated with the current source term. The specific ordinary differential equation is as follows: Where: d a is the damping coefficient, f is the source term, a is the active specific surface area, C CF is the concentration of carbon fluoride, F is the Faraday constant, V i is the stoichiometric coefficient, and n is the number of electrons involved in the electrochemical reaction.

5. A lithium battery electrochemical-thermal coupling modeling method according to claim 1, characterized in that: In step 4, the second one-dimensional electrochemical model is an optimized one-dimensional electrochemical model of a lithium / carbon fluoride battery, and the inverse problem model is an optimized model; The specific optimization process is as follows: the battery discharge curves obtained by experiment and simulation are compared respectively, and the mean square error value between the curves is used as the objective function to form an inverse problem model; given the initial value and interval of the parameter, a multi-parameter identification optimization algorithm is selected to adjust the parameter estimation value, and the first optimization tolerance is preset. After multiple iterations, the simulation results of the battery discharge curve and the experimental test results meet the set requirements, and the second one-dimensional electrochemical model is obtained.

6. A lithium battery electrochemical-thermal coupling modeling method according to claim 1, characterized in that: In step 5, the first electrochemical-thermal coupling model is an unoptimized electrochemical-thermal coupling model of a lithium / carbon fluoride battery, and the third physical field is a solid heat transfer field; the specific coupling method of the one-dimensional electrochemical model and the three-dimensional thermal model of the lithium / carbon fluoride battery is as follows: The volume average thermal power of the second one-dimensional electrochemical model is added to the three-dimensional thermal model as a heat source, and the average temperature of the three-dimensional thermal model is used as the reaction temperature of the second one-dimensional electrochemical model to affect the electrochemical reaction process in real time, thereby realizing the bidirectional coupling of one-dimensional electrochemistry and three-dimensional heat.

7. A lithium battery electrochemical-thermal coupling modeling method according to claim 1, characterized in that: In step 6, the second electrochemical-thermal coupling model is an optimized lithium / carbon fluoride battery electrochemical-thermal coupling model; the entropy thermal coefficient of the carbon fluoride material in the first lithium / carbon fluoride battery electrochemical-thermal coupling model is optimized, and the specific optimization process is as follows: First, the entropy thermal coefficient of the carbon fluoride material at different discharge depths is fitted into a polynomial, and the constant in the polynomial is set as an undetermined parameter. The battery temperature rise curves obtained by experiment and simulation are compared respectively, and the mean square error value between the curves is used as the objective function to construct an inverse problem model. The optimization algorithm of parameter identification is selected to adjust the above-mentioned undetermined parameters, and the second optimization tolerance is preset. After multiple iterations, the simulation results of the battery temperature rise and the experimental test results meet the set requirements, and the second electrochemical-thermal coupling model is obtained.

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