Modeling method for initial porosity of battery assembly based on mechanical-electric coupling relation

Abstract

The invention belongs to the technical field of multi-mode signal monitoring of a power and energy storage battery system, and particularly relates to an initial porosity modeling method of a battery assembly based on a mechanical-electric coupling relation, which comprises the following steps of: representing the initial porosity of each part of a battery by utilizing a mathematical model based on a measured force signal; a mathematical model between the porosity of the porous material of the battery and the external pressure is established, the initial porosity of each part of the battery is obtained, nondestructive identification of the initial porosity is realized, the performance evolution of the battery in the actual operation process can be accurately analyzed, technical support is provided for constructing an efficient and accurate battery numerical simulation model, and the method is suitable for popularization and application. The method does not need to damage the sample, and ensures the integrity of the sample material; the method is not influenced by environmental factors such as temperature and humidity, and the initial porosity of the assembly is calculated through a formula, so that measurement and characterization can be facilitated; meanwhile, the change condition of the porosity can be rapidly reflected in situ, data acquisition and post-processing can be completed in a short time, and the efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of multimodal signal monitoring of power and energy storage battery systems, and particularly relates to a method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship. Background Art

[0002] In the field of modern energy storage, lithium-ion batteries are widely used in electric vehicles, portable electronic devices, and renewable energy storage systems due to their high energy density and long cycle life. With the development of electric vehicles and renewable energy, the electrochemical performance, safety and stability of batteries are increasingly demanding. First of all, the porosity of battery component materials plays a vital role in battery performance. During the charge and discharge cycle of the battery, the electrode material may undergo structural deformation, such as expansion, peeling, or cracking, and the electrolyte may react with the electrode material to form a solid electrolyte interface (SEI) film, resulting in deposits, lithium dendrites, etc., resulting in a decrease in porosity.

[0003] Appropriate porosity not only optimizes the physical and chemical properties of ion channels and promotes the ion migration process in the electrolyte, which helps improve the battery's charge and discharge efficiency and rate, but also allows more active materials to contact the electrolyte, thereby increasing the battery's energy storage capacity. It can also reduce stress concentration and deformation during the charge and discharge process, thereby improving the battery's cycle life. However, excessively high porosity may lead to structural instability in the electrode material, affecting the battery capacity. At the same time, excessively high porosity can reduce the mechanical strength of the electrode, increase the risk of material cracking or peeling, and accelerate the decline in battery performance. Excessively low porosity, on the other hand, can lead to decreased ionic conductivity, weakened battery charge and discharge capabilities, and reduced battery performance. Secondly, the accurate acquisition of the initial porosity is also very important for the simulation accuracy.

[0004] Porosity is a critical parameter in battery simulation models. Because homogenized models are often used in battery simulation, it's difficult to fully consider the battery's microstructure and accurately simulate the internal processes of the electrode. Therefore, an inaccurate initial porosity can lead to significant deviations in the simulation model, reducing prediction accuracy. The porosity of each battery component's raw material state is measurable and known. However, during the manufacturing process, factors such as injection, formation, swelling, and assembly can cause deformation of the battery components, leading to changes in porosity. Therefore, to avoid a decrease in battery cycle life and reduced simulation model prediction accuracy due to porosity changes, it is crucial to accurately determine the porosity of the battery components.

[0005] At present, the testing methods for battery materials are mainly divided into two categories: destructive testing and non-destructive testing.

[0006] Traditional destructive testing methods, such as scanning electron microscopy (SEM) and X-ray computed tomography (CT), can provide accurate porosity data, but often require cutting or destroying the sample, rendering it unusable and increasing the complexity of the testing process. Specifically, SEM combines energy-dispersive X-ray analysis (EDX) with sample elemental composition to provide nanoscale surface topography and structural information. It can also acquire three-dimensional morphological information through various imaging modes. However, this testing method requires sample destruction for testing, which complicates sample preparation. Battery materials, in particular, require special processing to ensure accurate observation under vacuum. Consequently, SEM testing requires expensive equipment and maintenance. X-ray computed tomography (CT) can generate three-dimensional images of the battery's internal structure, facilitating the detection of defects or structural changes. It offers excellent imaging quality for different materials and can distinguish regions of varying density. However, its disadvantages include the need for specialized, high-energy X-ray equipment, which is costly; data acquisition and post-processing can be time-consuming; and radiation safety and protective measures must be considered during operation.

[0007] Non-destructive testing methods such as ultrasonic testing, acoustic emission testing, and electromagnetic testing can achieve the purpose of testing battery components while protecting the samples to the greatest extent. For example, ultrasonic testing can be performed without contacting the samples and is suitable for reusable battery materials.

[0008] However, its propagation speed will be affected by temperature. For example, in a high temperature environment, its propagation speed will increase, which may lead to a decrease in the detection depth and defect accuracy. Humidity will also affect propagation, especially in some occasions where a coupling agent is required. A high humidity environment may cause the performance of the coupling agent to change, thereby affecting the detection effect; and, compared with SEM and CT, ultrasound has a lower resolution and cannot detect tiny defects. At the same time, it is sensitive to environmental conditions and the test results are unstable. In addition, high-performance ultrasonic testing equipment is usually more expensive. For example, phased array ultrasonic testing equipment can provide higher resolution and deeper detection, but its purchase and maintenance costs are significantly higher than traditional ultrasonic equipment. In addition, the equipment requires regular calibration and maintenance, which increases operating costs. The data processing process is complicated and cannot meet the requirements of battery initial porosity determination.

[0009] Therefore, a new non-destructive identification technology is urgently needed to obtain the initial porosity of battery components. This technology should be able to quickly and in situ obtain porosity information while maintaining the integrity of battery components, thereby enabling the detection and evaluation of battery performance. Summary of the Invention

[0010] (1) Technical issues to be resolved

[0011] The technical problem to be solved by this invention is to address the deficiencies in the prior art and provide a method for modeling the initial porosity of lithium battery components based on electromechanical coupling. By measuring the battery's force signal and then using mathematical deduction to obtain the battery's actual initial porosity, this method can conveniently, quickly, and in situ reflect the changes in porosity, thereby resolving the difficulty in analyzing the structure-activity relationship between porosity and its electrochemical performance during the battery's charge and discharge processes.

[0012] (2) Technical solution

[0013] To solve the above technical problems, the present invention provides a method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship, the method comprising:

[0014] Step 1: Determine the baseline data, including the initial thickness t0 of the battery and the initial porosity Initial active material volume fraction and the initial inactive matter volume fraction

[0015] Step 2: Establish the actual active material volume fraction Actual thickness t1 after battery assembly, initial active material volume fraction A first relationship model between the initial thickness t0 of the battery;

[0016] and establish the actual inactive material volume fraction Actual thickness t1 after battery assembly, initial inactive material volume fraction A second relationship model between the initial thickness t0 of the battery;

[0017] Step 3: Calculate the deformation ε1 caused by the shrinkage of the battery cell, and according to the deformation theory,

[0018] The actual thickness t1 of the battery after assembly is calculated;

[0019] Step 4: Based on the first relationship model and the actual thickness t1 of the battery after assembly, the actual active material volume fraction is obtained The actual volume fraction of inactive material is obtained by the second relational model and the actual thickness t1 of the battery after assembly.

[0020] Step 5: From the actual initial porosity Actual active substance volume fraction Actual inactive substance volume fraction The principle that the three are equal to 1 is used to obtain the actual initial void ratio.

[0021] In step 1, the initial thickness t0 and initial porosity of the battery are obtained based on the original data provided by the battery manufacturer. Initial active material volume fraction and the initial inactive matter volume fraction And use this as a benchmark.

[0022] Wherein, in said step 2, as Figure 2 As shown in the figure, during the manufacturing process of the battery, factors such as liquid injection, formation, swelling, and assembly may cause deformation of the battery components. However, during the manufacturing process, since the active and inactive materials in the battery materials are solid, deformation is difficult to occur, and only the gaps are compressed to cause deformation of the battery materials.

[0023] Therefore, the volume of active and inactive substances does not change, thus establishing the actual active substance volume fraction Actual thickness t1 after battery assembly, initial active material volume fraction The first relationship model between the initial thickness of the battery t0 is shown in formula (1);

[0024] and establish the actual inactive material volume fraction Actual thickness t1 after battery assembly, initial inactive material volume fraction The second relationship model between the initial thickness of the battery t0 is shown in formula (2);

[0025] Formula (1) and formula (2);

[0026]

[0027] In step 3, the deformation ε1 caused by the shrinkage of the battery cell is calculated based on the unidirectional compression test of each battery component and the force signal provided by the battery manufacturer; the actual thickness t1 of the battery after assembly is calculated based on the known initial thickness t0 of the battery and the obtained deformation ε1 caused by the shrinkage of the battery cell according to deformation theory, as shown in formula (3);

[0028] t1=t0(1-ε1) (3).

[0029] In step 4, after the actual thickness t1 is obtained, the actual active material volume fraction is obtained by combining the relationship model of formula (1) and formula (3) The actual volume fraction of inactive substances is obtained by combining the relationship model of formula (2) with formula (3):

[0030] The relationship is expressed as follows:

[0031]

[0032] Wherein, in said step 5, the actual initial porosity Actual active substance volume fraction Actual inactive substance volume fraction The principle that the three are equal to 1 is used to obtain the actual initial void ratio. As shown in formula (6);

[0033]

[0034] (3) Beneficial effects

[0035] Compared with the existing technology, the beneficial effect of the present invention lies in that, based on the measured force signal, the scheme uses a mathematical model to establish the relationship between strain and the porosity of each battery component, and then calculates the actual initial porosity of each component after battery manufacturing, which can facilitate measurement and characterization, and quickly and in situ reflect the change of porosity. There is no need to cut or destroy the sample, and there is no need to use external non-destructive testing methods such as ultrasound and sound waves. The porosity of battery component materials can be detected, which reduces cost and energy consumption and improves efficiency and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the technical solution of the present invention.

[0037] Figure 2 Schematic diagram of the process of porosity and deformation of lithium-ion battery electrodes.

[0038] Figure 3 Schematic diagram of the process for obtaining and verifying the actual initial porosity.

[0039] Figure 4 The stress-strain curves of various components are shown in Figure 1. anode, b. cathode.

[0040] Figure 5 A comparison chart of the actual initial porosity errors of battery components. DETAILED DESCRIPTION

[0041] In order to make the purpose, content, and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below with reference to the accompanying drawings and examples.

[0042] The present invention uses a method of using a mathematical model to represent the initial porosity of each battery component based on the measured force signal, establishes a mathematical model between the porosity of the battery porous material and the external pressure, obtains the actual initial porosity of each battery component, and realizes non-destructive identification of the initial porosity, thereby accurately analyzing the performance evolution of the battery during actual operation, and providing technical support for the construction of an efficient and accurate battery numerical simulation model. This method does not require destruction of the sample, ensures the integrity of the sample material, and greatly reduces equipment costs and maintenance expenses; this method is also not affected by environmental factors such as temperature and humidity, and the initial porosity of the component is calculated by a formula, which can be convenient for measurement and characterization; at the same time, it can quickly and in situ reflect the changes in porosity, and data acquisition and post-processing can be completed in a relatively short time, improving efficiency.

[0043] To solve the above technical problems, the present invention provides a method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship, the method comprising:

[0044] Step 1: Determine the baseline data, including the initial thickness t0 of the battery and the initial porosity Initial active material volume fraction and the initial inactive matter volume fraction

[0045] Step 2: Establish the actual active material volume fraction Actual thickness t1 after battery assembly, initial active material volume fraction A first relationship model between the initial thickness t0 of the battery;

[0046] and establish the actual inactive material volume fraction Actual thickness t1 after battery assembly, initial inactive material volume fraction A second relationship model between the initial thickness t0 of the battery;

[0047] Step 3: Calculate the deformation ε1 caused by the shrinkage of the battery cell, and according to the deformation theory,

[0048] The actual thickness t1 of the battery after assembly is calculated;

[0049] Step 4: Based on the first relationship model and the actual thickness t1 of the battery after assembly, the actual active material volume fraction is obtained The actual volume fraction of inactive material is obtained by the second relational model and the actual thickness t1 of the battery after assembly.

[0050] Step 5: From the actual initial porosity Actual active substance volume fraction Actual inactive substance volume fraction The principle that the three are equal to 1 is used to obtain the actual initial void ratio.

[0051] In step 1, the initial thickness t0 and initial porosity of the battery are obtained based on the original data provided by the battery manufacturer. Initial active material volume fraction and the initial inactive matter volume fraction And use this as a benchmark.

[0052] Wherein, in said step 2, as Figure 2 As shown in the figure, during the manufacturing process of the battery, factors such as liquid injection, formation, swelling, and assembly may cause deformation of the battery components. However, during the manufacturing process, since the active and inactive materials in the battery materials are solid, deformation is difficult to occur, and only the gaps are compressed to cause deformation of the battery materials.

[0053] Therefore, the volume of active and inactive substances does not change, thus establishing the actual active substance volume fraction Actual thickness t1 after battery assembly, initial active material volume fraction The first relationship model between the initial thickness of the battery t0 is shown in formula (1);

[0054] and establish the actual inactive material volume fraction Actual thickness t1 after battery assembly, initial inactive material volume fraction The second relationship model between the initial thickness of the battery t0 is shown in formula (2);

[0055] Formula (1) and formula (2);

[0056]

[0057] In step 3, the deformation ε1 caused by the shrinkage of the battery cell is calculated based on the unidirectional compression test of each battery component and the force signal provided by the battery manufacturer; the actual thickness t1 of the battery after assembly is calculated based on the known initial thickness t0 of the battery and the obtained deformation ε1 caused by the shrinkage of the battery cell according to deformation theory, as shown in formula (3);

[0058] t1=t0(1-ε1) (3).

[0059] In step 4, after the actual thickness t1 is obtained, the actual active material volume fraction is obtained by combining the relationship model of formula (1) and formula (3) The actual volume fraction of inactive substances is obtained by combining the relationship model of formula (2) with formula (3):

[0060] The relationship is expressed as follows:

[0061]

[0062] Wherein, in said step 5, the actual initial porosity Actual active substance volume fraction Actual inactive substance volume fraction The principle that the three are equal to 1 is used to obtain the actual initial void ratio. As shown in formula (6);

[0063]

[0064] Example 1

[0065] This example uses a commercial soft-pack battery as an example to illustrate the process of obtaining and verifying the actual initial porosity ( Figure 3 The commercial soft pack battery has anode material of graphite coated on copper foil and cathode material of LiNi based on aluminum foil. 1 / 3Mn 1 / 3 Co 1 / 3 O2 (NMC), the separator uses a porous polyethylene-based membrane with a single-sided ceramic coating. In the absence of compressive force, the initial porosity of the anode is 0.310, and the initial porosity of the cathode is 0.330.

[0066] Step 1: With the known initial thickness t0 and initial porosity of the battery Initial active material volume fraction and the initial inactive matter volume fraction As a benchmark.

[0067] Step 2: Since the volumes of active and inactive substances remain unchanged, we can get the formula:

[0068]

[0069] In the formula is the actual active material volume fraction of the battery components after assembly, is the actual volume fraction of inactive materials in the battery after assembly, and t1 is the actual thickness of the battery after assembly.

[0070] Step 3: Perform uniaxial compression test on battery components to obtain stress-strain curves of each component, such as Figure 4 As shown in the stress-strain curve, it can be seen that stress increases with increasing strain. When the strain increases to a certain value, the stress will suddenly decrease if it continues to increase. Using the obtained stress-strain curve and the known stress, linear interpolation is applied to obtain the deformation ε1.

[0071] Step 4: Based on the known initial thickness of the battery and the obtained deformation caused by the shrinkage of the battery cell, the actual thickness t1 of the battery after assembly can be calculated according to deformation theory.

[0072] Step 5: After the actual thickness is introduced, the actual active material volume fraction is obtained by combining the formulas of step 4 and step 2 Actual inactive substance volume fraction

[0073] Step 6: The actual initial porosity, actual active material volume fraction, and actual inactive material volume fraction are all equal to 1, so the actual initial porosity can be obtained. Relationship with initial porosity and deformation.

[0074] Then the actual initial porosity of the anode and cathode components is calculated

[0075] Step 7: Table 2 shows the actual initial porosity of each component measured under three stresses. It can be seen that the actual initial porosity of each component decreases with the increase of stress. Under the same stress, the actual initial porosity of different components is different. The following is the error between the porosity of each component and the measured porosity. and mean relative error The formula is as follows:

[0076]

[0077]

[0078] In the above formula It is the actual initial porosity of the battery components after assembly, calculated by the formula in the battery component initial porosity modeling method based on the electromechanical coupling relationship. It is the actual initial porosity of the battery components after assembly, measured experimentally.

[0079] The comparison is shown in Table 3, and the error comparison diagram is drawn, as shown in Figure 5As shown in the figure and table, it can be seen that the initial porosity of the anode under 0MPa stress is 0.310. As the stress increases, the porosity gradually decreases to 0.260, with a maximum error of 2.90% and an average relative error of 2.30%. The initial porosity of the cathode under 0MPa stress is 0.330. As the stress increases, the porosity gradually decreases to 0.302, with a maximum error of 1.60% and an average relative error of 0.89%. As mentioned above, by comparing the calculation of the model formula with the actual initial porosity measured experimentally, the errors of the anode and cathode are both within 5%, and the change in porosity is predicted more accurately. Therefore, without any correction, this method can more accurately predict the change in porosity of the battery anode and cathode under different stress conditions, with high prediction accuracy. This method realizes non-destructive testing of the porosity of battery components, proving the effectiveness of the scheme.

[0080] Table 2 Porosity of key battery components under different stresses

[0081]

[0082] Table 3 Actual initial porosity of each battery component, calculated vs. experimental

[0083]

[0084]

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for modeling the initial porosity of a battery component based on electromechanical coupling, characterized in that: The method comprises: Step 1: Determine the baseline data, including the initial thickness t0 of the battery and the initial porosity Initial active material volume fraction and the initial inactive matter volume fraction Step 2: Establish the actual active material volume fraction Actual thickness t1 after battery assembly, initial active material volume fraction A first relationship model between the initial thickness t0 of the battery; and establish the actual inactive material volume fraction Actual thickness t1 after battery assembly, initial inactive material volume fraction A second relationship model between the initial thickness t0 of the battery; Step 3: Calculate the deformation ε1 caused by the shrinkage of the battery cell, and calculate the actual thickness t1 of the battery after assembly based on deformation theory; Step 4: Based on the first relationship model and the actual thickness t1 of the battery after assembly, the actual active material volume fraction is obtained The actual volume fraction of inactive material is obtained by the second relational model and the actual thickness t1 of the battery after assembly. Step 5: From the actual initial porosity Actual active substance volume fraction Actual inactive substance volume fraction The principle that the three are equal to 1 is used to obtain the actual initial void ratio.

2. The method for modeling the initial porosity of a battery component based on an electromechanical coupling relationship according to claim 1, wherein: In step 1, the initial thickness t0 and initial porosity of the battery are obtained based on the original data provided by the battery manufacturer. Initial active material volume fraction and the initial inactive matter volume fraction And use this as a benchmark.

3. The method for modeling the initial porosity of a battery component based on an electromechanical coupling relationship according to claim 2, wherein: In step 2, the battery components may be deformed due to factors such as liquid injection, formation, swelling, and assembly during the manufacturing process. However, since the active and inactive materials in the battery materials are solid during the manufacturing process, deformation is difficult to occur, and only the gaps are compressed to cause deformation of the battery materials. Therefore, the volume of active and inactive substances does not change, thus establishing the actual active substance volume fraction Actual thickness t1 after battery assembly, initial active material volume fraction The first relationship model between the initial thickness of the battery t0 is shown in formula (1); and establish the actual inactive material volume fraction Actual thickness t1 after battery assembly, initial inactive material volume fraction The second relationship model between the initial thickness of the battery t0 is shown in formula (2); Formula (1) and formula (2); 4. The method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship according to claim 3, wherein: In step 3, the deformation ε1 caused by the shrinkage of the battery cell is calculated based on the unidirectional compression test of each battery component and the force signal provided by the battery manufacturer; the actual thickness t1 of the battery after assembly is calculated based on the known initial thickness t0 of the battery and the obtained deformation ε1 caused by the shrinkage of the battery cell according to deformation theory, as shown in formula (3); t1=t0(1-ε1) (3).

5. The method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship according to claim 4, wherein: In step 4, after the actual thickness t1 is obtained, the actual active material volume fraction is obtained by combining the relationship model of formula (1) and formula (3) The actual volume fraction of inactive substances is obtained by combining the relationship model of formula (2) with formula (3): The relationship is expressed as follows:

6. The method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship according to claim 5, wherein: In step 5, the actual initial porosity Actual active substance volume fraction Actual inactive substance volume fraction The principle that the three are equal to 1 is used to obtain the actual initial void ratio. As shown in formula (6); 7. The method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship according to claim 6, wherein: The method measures the force signal of the battery and then uses mathematical deduction to obtain the actual initial porosity of the battery, thereby being able to conveniently, quickly and in situ reflect the change in porosity, thereby solving the problem of difficulty in analyzing the structure-activity relationship between porosity and its electrochemical performance during the battery's charge and discharge process.

8. The method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship according to claim 6, wherein: Based on the measured force signal, the method uses a mathematical model to establish the relationship between strain and the porosity of each battery component, and then calculates the actual initial porosity of each component after battery manufacturing, thereby facilitating measurement and characterization, and quickly and in situ reflecting changes in porosity.

9. The method for modeling the initial porosity of a battery assembly based on an electromechanical coupling relationship according to claim 6, wherein: The method can detect the porosity of battery component materials without cutting or destroying the sample and without using external non-destructive testing methods, thereby reducing costs and energy consumption.

10. The method for modeling the initial porosity of a battery component based on electromechanical coupling according to claim 6, wherein: The method is not affected by temperature and humidity environmental factors, and the initial porosity of the component is calculated through a formula, which facilitates measurement and characterization. At the same time, it can quickly and in situ reflect the changes in porosity, and data collection and post-processing can be completed in a relatively short time, thereby improving efficiency.

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