Electrode three-dimensional image correction-based battery electrochemical simulation and modeling method

Abstract

The invention relates to a battery electrochemical simulation and modeling method based on electrode three-dimensional image correction, which is characterized in that a basic electrochemical model is corrected on the basis of an electrode three-dimensional image output active material D50 diameter, electrode porosity, solid phase tortuosity and liquid phase tortuosity on the basis of a lithium ion battery basic P2D electrochemical model. Compared with the prior art, the generated high-fidelity electrochemical model of the lithium ion battery can express heterogeneity of a microstructure in an electrode, electrochemical behaviors of the battery under low-rate and high-rate charging and discharging working conditions can be accurately expressed under a set of electrochemical parameters, and the method has the advantages of being good in application prospect in guiding battery design and management. And the improvement of the comprehensive performance of the battery system is significant.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery modeling, and in particular to a battery electrochemical simulation and modeling method based on electrode three-dimensional image correction. Background Art

[0002] Lithium-ion batteries have become the main power source for pure electric vehicles and hybrid vehicles due to their high energy density, low self-discharge rate and long life, and are of great significance in alleviating energy depletion and environmental pollution problems.

[0003] Lithium-ion batteries are complex multi-physics systems with multiple physical and chemical processes taking place inside them. Accurate modeling of lithium-ion batteries is conducive to better battery design and battery management. For battery design, manufacturers currently often use a trial-and-error method, that is, to manufacture battery samples with different geometric structures, and obtain the mapping relationship between structure and performance through a series of electrochemical tests, so as to obtain the optimal battery structure that meets the expected requirements. This method requires a lot of manpower and material resources and often has a long development cycle. In contrast, by establishing a battery electrochemical model, battery performance can be predicted based on simulation methods, greatly saving development costs; for battery management, accurately estimating the battery's state of charge, health status, temperature and other information based on the electrochemical model during battery operation helps to keep the battery working within an appropriate range, improve battery safety performance and extend service life.

[0004] At present, the establishment of battery electrochemical models is mainly based on the traditional P2D theory, such as the "A lithium-ion battery electrochemical-thermal-mechanical coupling model and modeling method" disclosed in the invention patent with publication number CN110457742A; the "A lithium-ion battery multi-scale and multi-dimensional electrochemical-mechanical-thermal coupling model construction method" disclosed in the invention patent with publication number CN115238455A; the "electrochemical-thermal-structural coupling multi-scale modeling method for laminated lithium-ion batteries" disclosed in the invention patent with publication number CN112883610A. The P2D model assumes that the active particles are uniformly distributed spheres, and uses the Bruggeman relationship to approximate the effective transmission parameters of the solid-liquid phase, ignoring the heterogeneity of the structure in the electrode. Under low-rate charge and discharge conditions, the lithium ion concentration gradient is small, so the homogenized model can accurately express the internal and external characteristics of the battery; however, under high-rate charge and discharge conditions, the complex heterogeneity of the pores in the thickness direction limits the transmission of lithium ions, especially for thick electrodes. At this time, the homogenization model often underestimates the battery polarization, resulting in large errors between the simulation and experimental results and inaccurate models. Although the P2D model can accurately express the terminal voltage of the battery at a high rate through parameter identification and other methods, the model is actually distorted at this time, and the physical and chemical processes occurring inside it do not match the actual situation. Its credibility is greatly questioned when used for battery design and management. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art that the establishment of battery electrochemical model is mainly based on traditional P2D theory, ignoring the heterogeneity of the structure inside the electrode, and to provide a battery electrochemical simulation and modeling method based on electrode three-dimensional image correction.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A battery electrochemical simulation method based on electrode three-dimensional image correction includes the following steps: during the operation of the lithium-ion battery, estimating the state of charge, health state and temperature information of the lithium-ion battery based on a pre-constructed lithium-ion battery electrochemical model;

[0008] The lithium-ion battery electrochemical model is obtained by correcting the basic electrochemical model through the electrode three-dimensional image;

[0009] The basic electrochemical model includes a geometric model part, an electrochemical parameter part and a partial differential equation group part, which is used to solve the potential and Li in the solid / liquid phase of the battery. + Concentration distribution;

[0010] The electrode three-dimensional image is used to analyze the inhomogeneity of the structure inside the electrode and to correct the geometric model part.

[0011] Further, the geometric model part of the basic electrochemical model includes battery geometric parameters and electrode geometric parameters;

[0012] The battery geometric parameters include the length, width and thickness of the positive and negative electrodes; the length, width and thickness of the separator;

[0013] The electrode geometric parameters include the D50 diameter of the positive and negative electrode active materials, the porosity of the positive and negative electrodes, the solid phase tortuosity in three directions of the positive and negative electrodes, and the liquid phase tortuosity in three directions; the electrode geometric parameters are obtained from the electrode three-dimensional image.

[0014] Furthermore, the electrochemical parameter part of the basic electrochemical model includes active material parameters, electrolyte parameters and reaction kinetic parameters;

[0015] The active material parameters include solid phase diffusion coefficient, solid phase initial lithium ion concentration, solid phase maximum lithium insertion concentration, solid phase conductivity, electrode equilibrium potential and electrode working range;

[0016] The electrolyte parameters include liquid phase diffusion coefficient, liquid phase initial lithium ion concentration, liquid phase conductivity, transfer number and activity correlation;

[0017] The reaction kinetic parameters include reaction rate constants.

[0018] Furthermore, the partial differential equation group of the basic electrochemical model includes a solid phase mass transfer conservation equation, a solid phase charge transfer conservation equation, a liquid phase mass transfer conservation equation, a liquid phase charge transfer conservation equation and a Butler-Volmer reaction kinetic equation.

[0019] Furthermore, the electrode three-dimensional image includes a positive electrode three-dimensional real microstructure and a negative electrode three-dimensional real microstructure; the electrode three-dimensional image is obtained by imaging and processing technology.

[0020] The present invention also provides a battery electrochemical modeling method for implementing the battery electrochemical simulation method based on electrode three-dimensional image correction as described above, comprising the following steps:

[0021] S1: Measure the length, width and thickness of the positive and negative electrodes and the separator of the lithium-ion battery to be tested to obtain the battery geometric parameters;

[0022] S2: Obtain the three-dimensional real microstructure of the positive and negative electrodes of the lithium-ion battery to be tested, and segment the solid and liquid phases through image processing methods and statistically obtain the D50 diameter D of the positive electrode active material pos and the negative electrode active material D50 diameter D neg ;

[0023] S3: Divide the three-dimensional real microstructure of the positive electrode of the lithium-ion battery to be tested into N equal parts along the thickness direction, each with a thickness of d pos , the three-dimensional real microstructure of the negative electrode of the lithium-ion battery to be tested is divided into M equal parts along the thickness direction, each with a thickness of d neg ,The electrode geometric parameters of each electrode are obtained from the corresponding electrode three-dimensional image;

[0024] S4: According to the three-dimensional real microstructure of each equally divided positive electrode of the battery, the corresponding positive electrode active material D50 diameter, positive electrode electrode porosity, solid phase tortuosity in three directions of the positive electrode and liquid phase tortuosity in three directions, i.e., the electrode geometric parameters of the positive electrode are obtained respectively; according to the three-dimensional real microstructure of each equally divided negative electrode of the battery, the corresponding negative electrode active material D50 diameter, negative electrode electrode porosity, solid phase tortuosity in three directions of the negative electrode and liquid phase tortuosity in three directions, i.e., the electrode geometric parameters of the negative electrode are obtained respectively;

[0025] S5: Obtaining electrochemical parameters of active materials, electrochemical parameters of electrolyte and reaction kinetic parameters in the lithium-ion battery to be tested;

[0026] S6: Based on the theoretical framework of the P2D model, the geometric structures of the battery positive electrode, the battery negative electrode and the separator after each equal division in step S3 are established according to the battery geometric parameters obtained in step S1; the electrode geometric parameters obtained in step S4 are assigned to the geometric structures; the solid phase mass transfer conservation equation, the solid phase charge transfer conservation equation, the liquid phase mass transfer conservation equation, the liquid phase charge transfer conservation equation and the Butler-Volmer reaction kinetic equation are defined for the corresponding geometric structures, and the various electrochemical parameters obtained in step S5 are assigned to the variables of each equation to obtain the electrochemical model of the lithium ion battery;

[0027] S7: performing a discharge test on the lithium-ion battery to be tested to obtain experimental data, and verifying the accuracy of the electrochemical model of the lithium-ion battery based on the experimental data. If the verification passes, the electrochemical modeling of the lithium-ion battery to be tested is completed.

[0028] Further, in step S2, a focused ion beam-scanning electron microscope is used to obtain a two-dimensional image test set of the positive and negative electrodes of the lithium-ion battery to be tested, and then a three-dimensional reconstruction is performed in a three-dimensional visualization software to obtain a three-dimensional real microstructure of the positive and negative electrodes;

[0029] The image processing method for segmenting the solid and liquid phases is a threshold segmentation method.

[0030] Furthermore, in step S3, the principle of dividing the three-dimensional real microstructure of the positive electrode into N equal parts along the thickness direction is: to ensure that d pos Not less than D pos Under the premise of making N as large as possible; the principle of dividing the three-dimensional real microstructure of the negative electrode into M parts along the thickness direction is: to ensure d neg Not less than D neg Under the premise of making M as large as possible.

[0031] Further, in step S5, the electrochemical parameters of the active material include solid phase diffusion coefficient, solid phase initial lithium ion concentration, solid phase maximum lithium insertion concentration, solid phase conductivity, electrode equilibrium potential and electrode working range;

[0032] The electrochemical parameters of the electrolyte include liquid phase diffusion coefficient, liquid phase initial lithium ion concentration, liquid phase conductivity, transfer number and activity correlation;

[0033] The reaction kinetic parameters include reaction rate constants;

[0034] The solid phase diffusion coefficient, electrode equilibrium potential and reaction rate constant are obtained based on button half-cell testing;

[0035] The electrode working range is obtained based on button half-cell and full-cell tests, including first discharging the positive and negative button half-cells at a rate of 0.05C to obtain the equilibrium potential curves of the positive and negative electrode materials, and then discharging the full battery at a rate of 0.05C to obtain the equilibrium potential curve of the full battery, and finally using a genetic algorithm to identify the working ranges of the positive and negative electrodes respectively;

[0036] The solid phase initial lithium ion concentration, the solid phase maximum lithium insertion concentration, the solid phase conductivity, the liquid phase diffusion coefficient, the liquid phase initial lithium ion concentration, the liquid phase conductivity, the transfer number and the activity correlation adopt reference values ​​from literature.

[0037] Furthermore, in step S6, the geometric structure is arranged as follows: positive electrode N, positive electrode N-1, ..., positive electrode 1, separator, negative electrode 1, negative electrode 2, ..., negative electrode M; and the components of the geometric structure are bonded to each other to form a complete geometric model.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) The present invention proposes a battery electrochemical simulation and modeling method based on electrode three-dimensional image correction. The basic electrochemical model is constructed under the theoretical framework of the traditional P2D model. The three-dimensional real microstructure of the positive and negative electrodes is obtained using advanced imaging technology. The basic electrochemical model is corrected for heterogeneous distribution based on the output of the active material D50 diameter, electrode porosity, solid phase tortuosity and liquid phase tortuosity based on the electrode three-dimensional image. The influence of the complex internal geometric structure of the electrode on the effective transmission parameters is input into the basic electrochemical model. Compared with the traditional P2D model, the obtained high-fidelity electrochemical model can accurately express the electrochemical behavior of the battery under low-rate and high-rate charge and discharge conditions under a set of electrochemical parameters. This model is of great significance for guiding battery design and management and improving the comprehensive performance of battery systems.

[0040] (2) The present invention solves the problems of inaccurate simulation and internal mechanism distortion of the traditional P2D model at high magnification, and only uses the three-dimensional image of the electrode for correction. Its basic model framework is still the P2D theory, and the calculation cost will not increase significantly. The model proposed by the present invention can be further coupled with thermal, attenuation and other models to achieve a more accurate battery digital twin, which has important application value for battery design and battery management. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic diagram of the construction principle of a high-fidelity electrochemical model of a lithium-ion battery provided in an embodiment of the present invention;

[0042] Figure 2 A schematic diagram of a real three-dimensional image of a positive electrode and a negative electrode provided in an embodiment of the present invention;

[0043] Figure 3 A schematic diagram of a flow chart of a method for modeling a high-fidelity electrochemical model of a lithium-ion battery provided in an embodiment of the present invention;

[0044] Figure 4 A schematic diagram of the geometric structure of a model of this embodiment and comparative examples 1-5 provided in an embodiment of the present invention;

[0045] Figure 5 A comparison diagram of the terminal voltage of the present embodiment and the comparative examples 1-5 models under 0.2C discharge and the experimental results provided in the embodiments of the present invention;

[0046] Figure 6 This is a comparison chart of the terminal voltage of the present embodiment and the comparative examples 1-5 models under 1C discharge and the experimental results provided in the embodiments of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0048] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0050] Example 1

[0051] This embodiment provides a battery electrochemical simulation method based on electrode three-dimensional image correction, comprising the following steps: during the operation of the lithium-ion battery, estimating the state of charge, health state and temperature information of the lithium-ion battery based on a pre-constructed lithium-ion battery electrochemical model;

[0052] like Figure 1The figure shows the principle diagram of the high-fidelity electrochemical model of lithium-ion batteries in the present invention, which mainly includes the basic pseudo-two-dimensional (P2D) electrochemical model and the three-dimensional image of the electrode. The basic electrochemical model is established based on the porous electrode theory and the concentrated solution theory, assuming that the electrode particles are uniformly distributed spheres, and is used to solve the potential and Li in the solid / liquid phase of the battery. + Concentration distribution; The assumption of homogenization makes the model insufficient to describe the complex microstructure inside the electrode and cannot accurately express the internal and external characteristics of the battery, so the electrode three-dimensional image is used to analyze the inhomogeneity of the electrode structure. The high-fidelity electrochemical model proposed in the present invention is obtained by correcting the basic P2D electrochemical model with the electrode three-dimensional image, which has higher accuracy.

[0053] The basic electrochemical model consists of a geometric model part, an electrochemical parameter part, and a partial differential equation group part. The geometric model part is divided into battery geometric parameters and electrode geometric parameters. Battery geometric parameters include the length, width and thickness of the positive and negative electrodes, and the length, width and thickness of the separator; electrode geometric parameters include the D50 diameter of the positive and negative electrode active materials, the porosity of the positive and negative electrodes, the solid phase tortuosity in the three directions of the positive and negative electrodes, and the liquid phase tortuosity in the three directions. The electrode geometric parameters are obtained from the electrode three-dimensional image through advanced image processing algorithms.

[0054] The electrochemical parameters include active material parameters, electrolyte parameters and reaction kinetic parameters. Active material parameters include solid phase diffusion coefficient, solid phase initial lithium ion concentration, solid phase maximum lithium insertion concentration, solid phase conductivity, electrode equilibrium potential and electrode working range; electrolyte parameters include liquid phase diffusion coefficient, liquid phase initial lithium ion concentration, liquid phase conductivity, transfer number and activity correlation; reaction kinetic parameters include reaction rate constant.

[0055] The partial differential equations include the solid-phase mass transfer conservation equation, the solid-phase charge transfer conservation equation, the liquid-phase mass transfer conservation equation, the liquid-phase charge transfer conservation equation and the Butler-Volmer reaction kinetics equation.

[0056] The electrode 3D image includes the positive electrode 3D image and the negative electrode 3D image. The electrode 3D image is obtained by advanced imaging and processing technology, such as Figure 2 Shown is a true three-dimensional image of the positive and negative electrodes in this embodiment.

[0057] This embodiment also provides a modeling method for the high-fidelity electrochemical model of the lithium-ion battery. The overall process is as follows: Figure 3 As shown, the following steps are included:

[0058] S1: Measure the length, width and thickness of the positive and negative electrodes and the separator to obtain the battery geometric parameters.

[0059] The battery sample is a soft-pack battery with a nominal capacity of 1.2Ah. The length and width of the positive and negative electrodes and the separator were measured with a ruler, and the result was 60mm long and 55mm wide. Since the thickness of the positive and negative electrodes and the separator is at the micron level, a microscope is required to obtain it. In this embodiment, a cross-sectional polishing-scanning electron microscope (CP-SEM) is used to image the cross section of the battery, and the thickness of the positive electrode is 44.38μm, the thickness of the negative electrode is 50μm, and the thickness of the separator is 25μm.

[0060] S2: Obtain the local three-dimensional microstructure of the positive and negative electrodes, separate the solid and liquid phases through image processing methods, and statistically obtain the D50 diameter D of the positive and negative electrode active materials. pos and D neg .

[0061] In the present invention, a focused ion beam-scanning electron microscope (FIB-SEM) is used to obtain a two-dimensional image test set of positive and negative electrodes, and then three-dimensional reconstruction and subsequent processing are performed in the three-dimensional visualization software Avizo. Since the length (mm) and width (mm) and thickness (micrometer) of the positive and negative electrodes are at different length scales, it is impossible to obtain a three-dimensional image of the entire electrode, and an overly large image requires huge computing resources when processing, so this embodiment chooses to measure the local three-dimensional real structure of the electrode. The thickness of the three-dimensional structure is the same as that of the real electrode, and the length and width have the same statistical characteristics compared with the real electrode. The size of the positive electrode three-dimensional image is 44.38μm in length, 35μm in width, and 44.38μm in thickness. The size of the negative electrode three-dimensional image is 50μm in length, 50μm in width, and 50μm in thickness.

[0062] The imaging method used in the present invention is threshold segmentation, wherein the grayscale value range of the positive electrode solid phase is 28009-65535, and the grayscale value range of the positive electrode pore is 0-28008; the negative electrode adopts a different method from the positive electrode when acquiring the image, resulting in the solid phase being a low grayscale value area, ranging from 0-25147, and the liquid phase being a high grayscale value area, ranging from 25148-65535. By statistically quantifying the segmented positive and negative electrode active particles, the D50 diameter D of the positive electrode active particles is obtained. pos The D50 diameter of the negative electrode active particles is 2.17 μm. neg It is 4.31μm.

[0063] S3: Divide the positive electrode three-dimensional real microstructure into positive electrode 1, positive electrode 2, ..., positive electrode N along the thickness direction, and the thickness of each part is d pos ; The three-dimensional real microstructure of the negative electrode is divided into negative electrode 1, negative electrode 2, ..., negative electrode M along the thickness direction M, and the thickness of each part is d neg .

[0064] When the battery is charging, lithium ions are deintercalated on the surface of the positive electrode active particles and embedded on the surface of the negative electrode active particles, so a concentration gradient will appear in the thickness direction of the battery. Lithium ions are transferred from the positive electrode to the negative electrode under the action of the concentration difference and the electric field force, and the direction is opposite when the battery is discharged. The transmission of lithium ions is significantly affected by the internal microstructure of the electrode. However, the basic electrochemical model regards the electrode as a uniformly distributed whole, ignoring the effect of electrode structural heterogeneity on electrochemical behavior, which leads to the model's insufficient description of battery polarization phenomena. In order to make the basic electrochemical model have the ability to express structural heterogeneity, the present invention proposes to divide the electrode into multiple parts evenly in the thickness direction, and the electrode geometric parameters of each electrode are obtained from the corresponding electrode three-dimensional image.

[0065] In particular, the number of equal parts of the electrode is a key variable that affects the accuracy of the model. In theory, the more equal parts the model has, the closer it is to the real electrode structure. However, since the model is still established under the P2D theoretical framework, although the electrode thickness is small enough, its geometric structure still needs to be represented by the D50 diameter of the active particles, so the electrode thickness should be greater than the D50 diameter of the active particles, otherwise the result obtained when counting the D50 diameter of the active particles in the three-dimensional image of the electrode after equalization is inaccurate (too small), affecting the accuracy of the model.

[0066] In this embodiment, the positive and negative electrodes are evenly divided into 8 parts, and the thickness of each positive electrode and negative electrode is 5.5475 μm and 6.25 μm respectively. The diameter D50 of the positive active particles obtained from S2 is pos The diameter of the negative electrode active particles D50 is 2.17 μm. neg The electrode thickness is greater than the D50 diameter of the active particles.

[0067] S4: According to the three-dimensional real microstructures of positive electrode 1, positive electrode 2, ..., positive electrode 8, the corresponding positive electrode active material D50 diameter, positive electrode electrode porosity, solid phase tortuosity in three directions of the positive electrode and liquid phase tortuosity in three directions are obtained respectively; according to the three-dimensional real microstructures of negative electrode 1, negative electrode 2, ..., negative electrode 8, the corresponding negative electrode active material D50 diameter, negative electrode electrode porosity, solid phase tortuosity in three directions of the negative electrode and liquid phase tortuosity in three directions are obtained respectively to obtain the electrode geometric parameters.

[0068] Among them, the D50 diameter and porosity of the active material are the geometric parameters that need to be input in the P2D model to determine the electrode geometry; the solid phase tortuosity in three directions is used to correct the effective conductivity of the active material, and the liquid phase tortuosity in three directions is used to correct the effective diffusion coefficient and effective conductivity of the electrolyte.

[0069] S5: Obtain electrochemical parameters of active materials and electrolyte, and obtain reaction kinetic parameters.

[0070] The electrochemical parameters of the active material include solid phase diffusion coefficient, solid phase initial lithium ion concentration, solid phase maximum lithium insertion concentration, solid phase conductivity, electrode equilibrium potential and electrode working range; the electrochemical parameters of the electrolyte include liquid phase diffusion coefficient, liquid phase initial lithium ion concentration, liquid phase conductivity, transfer number and activity correlation; the reaction kinetic parameters include reaction rate constant.

[0071] The solid phase diffusion coefficient, electrode equilibrium potential and reaction rate constant are obtained based on button half-cell testing. In this embodiment, the solid phase diffusion coefficient is obtained based on constant current intermittent titration technique (GITT), the electrode equilibrium potential is obtained by discharging the button half-cell at a rate of 0.05C, and the reaction rate constant is obtained based on linear sweep voltammetry (LSV). The solid phase diffusion coefficient and reaction rate constant are related to the battery state of charge (SOC). In this embodiment, GITT and LSV tests are performed every 5% SOC to obtain the functional relationship between the electrochemical parameters and SOC.

[0072] The electrode working range is obtained based on button half-cell and full-cell tests. Specifically, the positive and negative button half-cells are first discharged at a rate of 0.05C to obtain the equilibrium potential curves of the positive and negative electrode materials, respectively. Then, the full cell is discharged at a rate of 0.05C to obtain the equilibrium potential curve of the full cell. Finally, a genetic algorithm (GA) is used to identify the working ranges of the positive and negative electrodes, respectively.

[0073] The remaining electrochemical parameters, i.e., the initial lithium ion concentration in the solid phase, the maximum lithium insertion concentration in the solid phase, the solid phase conductivity, the liquid phase diffusion coefficient, the initial lithium ion concentration in the liquid phase, the liquid phase conductivity, the transfer number and the activity correlation adopt reference values ​​from the literature. Specifically, the parameters used in this embodiment are derived from the literature (HE T, ZHANG T, WANG Z, et al. A comprehensive numerical study on electrochemical-thermal models of a cylindrical lithium-ion battery during discharge process [J]. ApplEnerg, 2022, 313: 10.1016 / j.apenergy.2022.118797.).

[0074] S6: Establish an electrochemical model based on the battery geometric parameters in the finite element software, and assign the electrochemical parameters and electrode geometric parameters to the model.

[0075] In this embodiment, the finite element software used is COMSOL. According to the length, width and thickness of the 8 positive electrodes, 8 negative electrodes and the separator in S3, the corresponding geometric structure is established in COMSOL in the form of a three-dimensional cuboid, where the thickness of the positive electrode collector is 12 μm, and the thickness of the negative electrode collector is 6 μm, as shown in FIG. Figure 4 As shown in the embodiment, the positive electrode current collector, positive electrode 8, positive electrode 7, ..., positive electrode 1, separator, negative electrode 1, negative electrode 2, ..., negative electrode 8, and negative electrode current collector are closely attached to form a complete full battery geometry.

[0076] In COMSOL, a group of partial differential equations is defined for each part, mainly including the solid-phase mass transfer conservation equation, the solid-phase charge transfer conservation equation, the liquid-phase mass transfer conservation equation, the liquid-phase charge transfer conservation equation and the Butler-Volmer reaction kinetics equation.

[0077] In this embodiment, unless otherwise specified, the parameter subscript s represents a solid phase related parameter, and the subscript e represents a liquid phase related parameter.

[0078] Solid phase mass transfer conservation equation:

[0079]

[0080] In the formula, c s is the solid phase lithium concentration, t is the time, r is the radius of the spherical coordinate system established with the center of the spherical particle as the origin, D s is the solid phase diffusion coefficient.

[0081] Solid phase charge transfer conservation equation:

[0082]

[0083] In the formula, is the effective electronic conductivity of the solid phase material ( Among them, σ s is the electronic conductivity of the solid phase material, ε is the electrode porosity, τ s is the solid phase tortuosity), φ s is the solid phase potential, S a is the specific surface area of ​​the solid phase material, r s is the particle radius of the solid phase material, which is half of the D50 diameter of the active material. loc is the local current density.

[0084] According to the solid charge transfer conservation equation, the battery terminal voltage (V) is defined as the difference between the positive electrode solid phase potential and the negative electrode solid phase potential.

[0085] Liquid phase mass transfer conservation equation:

[0086]

[0087] Where ε is the electrode porosity, c e is the liquid phase lithium ion concentration, t is the time, is the effective diffusion coefficient of lithium ions in liquid phase ( Among them, D e is the liquid phase diffusion coefficient, ε is the electrode porosity, τ e is the liquid phase tortuosity), S a is the specific surface area of ​​the solid phase material, i loc is the local current density, F is the Faraday constant, t + is the liquid phase ion transfer number.

[0088] Liquid phase charge transfer conservation equation:

[0089]

[0090] In the formula, is the liquid effective conductivity ( Among them, σ e is the electronic conductivity of the liquid phase material, ε is the electrode porosity, τ e is the liquid phase tortuosity), φ e is the liquid phase potential, R is the ideal gas constant, T is the temperature, F is the Faraday constant, f is the activity correlation, c e is the liquid phase lithium ion concentration, t + is the liquid phase ion transfer number, S a is the specific surface area of ​​the solid phase material, i loc is the local current density.

[0091] Butler-Volmer reaction kinetic equation:

[0092]

[0093] η=φ s -φ e -E eq

[0094] In the formula, i loc is the local current density, i0 is the exchange current density, α is the charge transfer coefficient, η is the electrode overpotential, F is the Faraday constant, R is the ideal gas constant, T is the temperature, k is the reaction rate constant, c s,max is the maximum lithium insertion concentration in the solid phase, c s,surf is the lithium ion concentration on the ion surface, c e is the liquid phase lithium ion concentration, c e,ref =1000mol / L is the initial lithium ion concentration in the liquid phase, φ s is the solid phase potential, φ e is the liquid phase potential, E eq is the electrode equilibrium potential.

[0095] The electrochemical parameters obtained by S5 and the electrode geometric parameters obtained by S4 are assigned to the above partial differential equation variables.

[0096] S7 performs discharge tests on battery samples at 0.2C and 1C rates, verifies the accuracy of the high-fidelity electrochemical model established above based on the experimental data, and completes the modeling work. Figure 5 The discharge voltage curve at 1C rate is compared with the experimental one. Figure 6 The constructed model has high accuracy at both small magnification (0.2C) and large magnification (1C).

[0097] Comparative experiment: Comparative Examples 1-5 were constructed for comparison with the solution of this embodiment, and the specific process is as follows:

[0098] On the basis of the embodiment, comparative example 1 adopts the basic P2D electrochemical model for modeling, and does not use the electrode three-dimensional image for any correction. The other conditions are the same as those of the embodiment, such as Figure 4 As shown in Comparative Example 1; Comparative Example 2 does not further separate the positive and negative electrodes in S3, and uses the entire electrode three-dimensional image to correct the single-layer electrode. The other conditions are the same as those in the embodiment, such as Figure 4 As shown in Comparative Example 2; Comparative Example 3, in S3, the positive and negative electrodes are divided into two equal parts, and the two layers of electrodes are corrected using the three-dimensional images of the electrodes that are equally divided. The other conditions are the same as those in the embodiment, such as Figure 4 As shown in Comparative Example 3; Comparative Example 4, in S3, the positive and negative electrodes are divided into four equal parts, and the four layers of electrodes are corrected using the three-dimensional images of the electrodes that are equally divided. The other conditions are the same as those in the embodiment, such as Figure 4 As shown in Comparative Example 4; Comparative Example 5, in S3, the positive and negative electrodes are divided into 16 equal parts, and the 16 layers of electrodes are corrected using the three-dimensional images of the electrodes that are equally divided. The other conditions are the same as those in the embodiment, such as Figure 4 As shown in Comparative Example 5.

[0099] Similarly, the model established in Comparative Examples 1-5 was simulated at 0.2C and 1C discharge rates to obtain discharge voltage curves, such as Figure 5 and Figure 6 shown.

[0100] Depend on Figure 5 It can be seen from the figure that at a small rate (0.2C), the discharge voltage curves of the basic P2D electrochemical model and the modified model with different layers basically coincide with each other, and there is no difference in simulation accuracy; however, at a large rate (1C), Figure 6From a) in the figure, it can be seen that the model established in the embodiment has the highest degree of match with the experimental results, and the models in comparative examples 1-5 all show insufficient polarization. This is because the homogenization assumption of the electrode ignores the heterogeneous structure inside the electrode, thereby insufficiently describing the battery polarization phenomenon. Figure 6 b) in the figure shows the root mean square error (RMSE) of different models relative to the experimental results, which is calculated as:

[0101]

[0102] Where n is the number of sampling points, V i is the terminal voltage obtained experimentally at the sampling point, v i is the terminal voltage at the sampling point obtained through simulation.

[0103] Depend on Figure 6 It can be seen intuitively in b) that the error of the uncorrected model is the largest. As the number of layers of the electrode in the thickness direction increases, the model's ability to describe the geometric heterogeneity in the thickness direction increases, and the terminal voltage simulation error gradually decreases. However, when the positive and negative electrodes are divided into 16 layers, the accuracy of the model begins to decrease. At this time, the thickness of each positive electrode is 2.77μm, and the thickness of each negative electrode is 3.15μm. Since the diameter D50 of the positive active particles obtained from S2 is pos The diameter of the negative electrode active particles D50 is 2.17 μm. neg It is 4.31μm. At this time, the thickness of the positive electrode is equivalent to the D50 diameter of the positive electrode active material, and the thickness of the negative electrode is smaller than the D50 diameter of the negative electrode active particle. Therefore, after the segmentation of the positive and negative electrode three-dimensional images, each electrode cannot contain a complete active particle, and the statistically obtained D50 diameter is inaccurate, which ultimately leads to the distortion of the model.

[0104] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A battery electrochemical simulation method based on electrode three-dimensional image correction, characterized in that: The method comprises the following steps: during the operation of the lithium-ion battery, estimating the state of charge, health state and temperature information of the lithium-ion battery based on a pre-built electrochemical model of the lithium-ion battery; The lithium-ion battery electrochemical model is obtained by correcting the basic electrochemical model through the electrode three-dimensional image; The basic electrochemical model includes a geometric model part, an electrochemical parameter part and a partial differential equation group part, which is used to solve the potential and Li in the solid / liquid phase of the battery. + Concentration distribution; The electrode three-dimensional image is used to analyze the inhomogeneity of the structure inside the electrode and to correct the geometric model part.

2. A battery electrochemical simulation method based on electrode three-dimensional image correction according to claim 1, characterized in that: The geometric model part of the basic electrochemical model includes battery geometric parameters and electrode geometric parameters; The battery geometric parameters include the length, width and thickness of the positive and negative electrodes; the length, width and thickness of the separator; The electrode geometric parameters include the D50 diameter of the positive and negative electrode active materials, the porosity of the positive and negative electrodes, the solid phase tortuosity in three directions of the positive and negative electrodes, and the liquid phase tortuosity in three directions; the electrode geometric parameters are obtained from the electrode three-dimensional image.

3. A battery electrochemical simulation method based on electrode three-dimensional image correction according to claim 1, characterized in that: The electrochemical parameter part of the basic electrochemical model includes active material parameters, electrolyte parameters and reaction kinetic parameters; The active material parameters include solid phase diffusion coefficient, solid phase initial lithium ion concentration, solid phase maximum lithium insertion concentration, solid phase conductivity, electrode equilibrium potential and electrode working range; The electrolyte parameters include liquid phase diffusion coefficient, liquid phase initial lithium ion concentration, liquid phase conductivity, transfer number and activity correlation; The reaction kinetic parameters include reaction rate constants.

4. A battery electrochemical simulation method based on electrode three-dimensional image correction according to claim 1, characterized in that: The partial differential equation group of the basic electrochemical model includes a solid phase mass transfer conservation equation, a solid phase charge transfer conservation equation, a liquid phase mass transfer conservation equation, a liquid phase charge transfer conservation equation and a Butler-Volmer reaction kinetic equation.

5. The battery electrochemical simulation method based on electrode three-dimensional image correction according to claim 1, characterized in that: The electrode three-dimensional image includes the positive electrode three-dimensional real microstructure and the negative electrode three-dimensional real microstructure; the electrode three-dimensional image is obtained by imaging and processing technology.

6. A battery electrochemical modeling method for realizing a battery electrochemical simulation method based on electrode three-dimensional image correction as described in any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Measure the length, width and thickness of the positive and negative electrodes and the separator of the lithium-ion battery to be tested to obtain the battery geometric parameters; S2: Obtain the three-dimensional real microstructure of the positive and negative electrodes of the lithium-ion battery to be tested, and segment the solid and liquid phases through image processing methods and statistically obtain the D50 diameter D of the positive electrode active material pos and the negative electrode active material D50 diameter D neg ; S3: Divide the three-dimensional real microstructure of the positive electrode of the lithium-ion battery to be tested into N equal parts along the thickness direction, each with a thickness of d pos , the three-dimensional real microstructure of the negative electrode of the lithium-ion battery to be tested is divided into M equal parts along the thickness direction, each with a thickness of d neg ,The electrode geometric parameters of each electrode are obtained from the corresponding electrode three-dimensional image; S4: According to the three-dimensional real microstructure of each equally divided positive electrode of the battery, the corresponding positive electrode active material D50 diameter, positive electrode electrode porosity, solid phase tortuosity in three directions of the positive electrode and liquid phase tortuosity in three directions, i.e., the electrode geometric parameters of the positive electrode are obtained respectively; according to the three-dimensional real microstructure of each equally divided negative electrode of the battery, the corresponding negative electrode active material D50 diameter, negative electrode electrode porosity, solid phase tortuosity in three directions of the negative electrode and liquid phase tortuosity in three directions, i.e., the electrode geometric parameters of the negative electrode are obtained respectively; S5: Obtaining electrochemical parameters of active materials, electrochemical parameters of electrolyte and reaction kinetic parameters in the lithium-ion battery to be tested; S6: Based on the theoretical framework of the P2D model, the geometric structures of the battery positive electrode, the battery negative electrode and the separator after each equal division in step S3 are established according to the battery geometric parameters obtained in step S1; the electrode geometric parameters obtained in step S4 are assigned to the geometric structures; the solid phase mass transfer conservation equation, the solid phase charge transfer conservation equation, the liquid phase mass transfer conservation equation, the liquid phase charge transfer conservation equation and the Butler-Volmer reaction kinetic equation are defined for the corresponding geometric structures, and the various electrochemical parameters obtained in step S5 are assigned to the variables of each equation to obtain the electrochemical model of the lithium ion battery; S7: performing a discharge test on the lithium-ion battery to be tested to obtain experimental data, and verifying the accuracy of the electrochemical model of the lithium-ion battery based on the experimental data. If the verification passes, the electrochemical modeling of the lithium-ion battery to be tested is completed.

7. The battery electrochemical modeling method according to claim 6, characterized in that: In step S2, a focused ion beam-scanning electron microscope is used to obtain a two-dimensional image test set of the positive and negative electrodes of the lithium-ion battery to be tested, and then a three-dimensional reconstruction is performed in a three-dimensional visualization software to obtain a three-dimensional real microstructure of the positive and negative electrodes; The image processing method for segmenting the solid and liquid phases is a threshold segmentation method.

8. The battery electrochemical modeling method according to claim 6, characterized in that: In step S3, the principle of dividing the three-dimensional real microstructure of the positive electrode into N equal parts along the thickness direction is: to ensure that d pos Not less than D pos Under the premise of making N as large as possible; the principle of dividing the three-dimensional real microstructure of the negative electrode into M parts along the thickness direction is: to ensure d neg Not less than D neg Under the premise of making M as large as possible.

9. The battery electrochemical modeling method according to claim 6, characterized in that: In step S5, the electrochemical parameters of the active material include solid phase diffusion coefficient, solid phase initial lithium ion concentration, solid phase maximum lithium insertion concentration, solid phase conductivity, electrode equilibrium potential and electrode working range; The electrochemical parameters of the electrolyte include liquid phase diffusion coefficient, liquid phase initial lithium ion concentration, liquid phase conductivity, transfer number and activity correlation; The reaction kinetic parameters include reaction rate constants; The solid phase diffusion coefficient, electrode equilibrium potential and reaction rate constant are obtained based on button half-cell testing; The electrode working range is obtained based on button half-cell and full-cell tests, including first discharging the positive and negative button half-cells at a rate of 0.05C to obtain the equilibrium potential curves of the positive and negative electrode materials, and then discharging the full battery at a rate of 0.05C to obtain the equilibrium potential curve of the full battery, and finally using a genetic algorithm to identify the working ranges of the positive and negative electrodes respectively; The solid phase initial lithium ion concentration, the solid phase maximum lithium insertion concentration, the solid phase conductivity, the liquid phase diffusion coefficient, the liquid phase initial lithium ion concentration, the liquid phase conductivity, the transfer number and the activity correlation adopt reference values ​​from literature.

10. The battery electrochemical modeling method according to claim 6, characterized in that: In step S6, the geometric structure is arranged as follows: positive electrode N, positive electrode N-1, ..., positive electrode 1, separator, negative electrode 1, negative electrode 2, ..., negative electrode M; the various components of the geometric structure are fitted together to form a complete geometric model.

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