Method and system for evaluating battery performance by using flexibility of pole piece and electronic equipment

Abstract

The invention relates to a method and system for evaluating battery performance by using flexibility of a pole piece and electronic equipment, and belongs to the technical field of lithium ion batteries. The method comprises the following steps: S1, winding a battery pole piece with set compaction density to obtain a winding diameter corresponding to a crack-free state as the flexibility of the pole piece; s2, processing the battery pole piece into a battery cell, and detecting the electrical property of the battery cell; s3, calculating the product of the compaction density of the battery pole piece and the flexibility of the pole piece, and obtaining a corresponding relation table of the product and the electrical performance in the S2; and S4, measuring the flexibility and the compaction density of the pole piece with unknown electrical performance, calculating the product, and querying the electrical performance in the corresponding range of the product numerical value in the relation table obtained in the S3 as the electrical performance of the battery prepared by the pole piece with unknown electrical performance. Through tests, the flexibility of the pole piece is quantified, a corresponding relation with the electrical performance of the battery is realized, the electrical performance of the battery can be evaluated in advance according to the flexibility and the compaction density of the pole piece, and the experiment cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a method, system and electronic equipment for evaluating battery performance by utilizing the flexibility of pole pieces. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Among the key manufacturing processes of lithium batteries, the manufacturing technology of electrodes and pole pieces is particularly important. After the electrode material is coated on the surface of the pole piece, the gaps between the various components of the material are large. If used directly, it is not only easy to shed powder but also difficult to achieve the target performance. The roller pressing process is used to compact the various granular materials on the electrode to a set density, increase the bonding force between the materials and between the materials and the foil, improve the peel strength, and thus improve the ion transmission capacity. However, the higher the compaction density, the better. The appropriate compaction density can not only ensure the flexibility of the pole piece, prevent the occurrence of broken belts in the production process, and improve the production yield; it can also improve the pole piece's absorption performance of the electrolyte, ensure that the pole piece is fully infiltrated, and thus improve the electrical performance. Therefore, in the research and development and production process of batteries, it is very important to test the flexibility of the pole piece.

[0004] Existing technologies include using plug gauges to obtain deformation data, and other solutions that provide electrode flexibility testing devices and electrode processing equipment to measure the tension experienced by the electrode. However, these methods lack close integration with the manufacturing process, making it difficult to directly evaluate battery performance using the test results. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method, system, and electronic device for evaluating battery performance using electrode flexibility. By using a winding method to obtain a value that characterizes electrode flexibility, combined with compaction density to evaluate battery performance, this method effectively guides actual production process design based on target performance.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for evaluating battery performance using electrode flexibility comprises the following steps:

[0008] S1. Winding battery pole pieces with different set compaction densities to obtain a winding diameter corresponding to a crack-free state as the pole piece flexibility;

[0009] S2. Process all the battery electrodes without cracks in S1 into battery cells and test their electrical properties respectively;

[0010] S3. Calculate the product of the compaction density and the flexibility of the battery electrode, and obtain a corresponding relationship table between the product and the electrical properties in S2;

[0011] S4. Measure the flexibility and compaction density of the electrode with unknown electrical properties and calculate the product. Query the relationship table obtained in S3 for the electrical properties within the corresponding range of the product value, and use this as the electrical properties of the battery prepared from the electrode with unknown electrical properties.

[0012] Optionally, in S1, the winding method is: winding the battery electrode closely around a rod-shaped mold with different set diameters for one or more times.

[0013] Optionally, in S1, the battery electrode is folded in half before winding, and the diameter of the rod-shaped mold is selected according to the width of the crack area at the fold position.

[0014] Optionally, in S2, the electrical performance includes: energy density, constant current charging ratio and cycle capacity retention rate.

[0015] Optionally, energy density refers to the ratio of the energy released by the battery to the mass of the battery when the battery is discharged to a set voltage.

[0016] The constant current charging ratio refers to the percentage of constant current charging capacity to the total charging capacity when the battery cell is charged to the set voltage using constant current and constant voltage.

[0017] The method for obtaining the cycle capacity retention rate is: after charging and discharging the battery at a set voltage of 1C / 1C once, the battery discharge capacity at this time is obtained as C0, and then after charging and discharging at a set number of 1C / 1C under normal temperature conditions, the battery discharge capacity at this time is obtained as C1. The cycle capacity retention rate = (C1 / C0)*100%.

[0018] Optionally, the relational table in S3 is a two-dimensional table.

[0019] Optionally, in S3, a fitting expression is obtained according to the two-dimensional table, including:

[0020] The relationship between energy density y and product x satisfies: y = 0.03x 2 +0.42x+159.5;

[0021] The relationship between the 2C charging constant current ratio z and the product x satisfies: z = -0.006x 2 +0.07x+98;

[0022] The relationship between the capacity retention rate F(x) and the product x after 700 cycles at room temperature satisfies the formula F(x) = -0.02x 3 +0.35x 2 -1.8x+100.

[0023] Optionally, in S4, the compaction density is the mass of the electrode coating per unit volume on the electrode sheet after rolling and drying.

[0024] In a second aspect, a system for implementing the above-mentioned method for evaluating battery performance using electrode flexibility includes:

[0025] A first calculation module is used to obtain the electrode flexibility of a battery electrode with a set compaction density;

[0026] The second calculation module is used to obtain the electrical performance of the battery electrode after being processed into a battery cell;

[0027] The third calculation module is used to calculate the product of the compaction density of the battery electrode and the flexibility of the electrode, and obtain a corresponding relationship table of the electrical performance of the product;

[0028] The fourth calculation module is used to calculate the product of the flexibility and compaction density of the electrode with unknown electrical properties, and obtain the electrical properties of the battery prepared by the electrode with unknown electrical properties according to the corresponding relationship table.

[0029] Optionally, the electrical properties include energy density, constant current charging ratio and cycle capacity retention rate.

[0030] In a third aspect, an electronic device comprises: a memory, a processor, and a program or instruction stored in the memory and executable on the processor, wherein the program or instruction, when executed by the processor, implements the steps in the above-mentioned method for evaluating battery performance using electrode flexibility.

[0031] The beneficial effects of the present invention are:

[0032] Among the components of a battery, the flexibility and compaction density of the positive electrode are related to each other. Appropriate compaction and toughness can ensure the processing yield of the electrode and the energy density of the battery. When the compaction density is low, the toughness is good, but the particle compaction density is not enough, and the material advantages are not fully utilized. When the compaction density is too high, although the energy density is improved, the brittleness of the electrode will also increase, and the process processing and short-term performance will deteriorate. The present invention quantifies the flexibility of the electrode through experiments and establishes a corresponding relationship with the electrical performance of the battery. It can be used to evaluate the electrical performance of the battery in advance based on the flexibility and compaction density of the electrode, thereby reducing experimental costs. On the other hand, the target electrical performance can be designed first, and the optimal compaction density parameters output in the manufacturing process can be designed according to the corresponding relationship table. The lower the target electrical performance requirements, the larger the upper and lower limits of the product value that can be used, and the higher the target electrical performance requirements, the smaller the upper and lower limits of the product value that can be used, thereby improving the production yield and the stability of the battery performance, reducing R&D costs and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 This is a diagram of the winding results in Example 1 of the present invention.

[0035] Figure 2 This is a scatter plot in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0037] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0038] In the following specific embodiments, the surface density of the battery electrode is 300-400 g / m 2 .

[0039] In the following specific embodiments, the compacted density is 2.2 to 2.6 g / cm 3 .

[0040] In the following specific embodiments, the processing of the battery cell includes: preparing a slurry of active material, conductive agent and binder through a slurry mixing process, then coating the slurry onto a current collector according to a set surface density, and compacting the slurry according to a set compaction density after baking.

[0041] Example 1

[0042] A method for evaluating battery performance using electrode flexibility comprises the following steps:

[0043] A positive electrode sheet is prepared, which includes a positive electrode collector, and positive electrode active material layers are respectively provided on the two surfaces of the positive electrode collector; the raw materials for preparing the positive electrode active material layer include positive electrode active material, conductive agent and binder, and the preparation method is: lithium iron phosphate, conductive carbon black and PVDF are uniformly mixed in a slurry mixing tank in a ratio of 97:1:2, and then coated on both sides on the surface of the current collector foil, compacted and baked to obtain the positive electrode sheet.

[0044] Among them, the coating surface density of the first group of positive electrode sheets is 300g / m 2 , and according to 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 and 2.6 g / cm 3 After rolling with a compaction density of 10000, it is cut into rectangular electrode membranes of 10*40cm.

[0045] The coating area density of the second group of positive electrode sheets is 320g / m 2 , and according to 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 and 2.6 g / cm 3 After rolling with a compaction density of 10000, it is cut into rectangular electrode membranes of 10*40cm.

[0046] The coating surface density of the third group of positive electrode sheets is 350g / m 2 , and according to 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 and 2.6 g / cm 3 After rolling with a compaction density of 10000, it is cut into rectangular electrode membranes of 10*40cm.

[0047] The coating surface density of the fourth group of positive electrode sheets is 400g / m 2 , and according to 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 and 2.6 g / cm 3 After rolling with a compaction density of 10000, it is cut into rectangular electrode membranes of 10*40cm.

[0048] Each group of positive electrode sheets is wound tightly against glass rods of different set sizes. The winding method is: the 10 cm edge is tightly against the upper glass rod, and the 40 cm edge is wound circumferentially on the glass rod. Since the winding diameter is the smallest when the first circle is wound, it can best reflect the flexibility of the electrode sheet. Therefore, it can be loosened after one circle to observe the state of the electrode sheet. When the glass rod is too thin, it can be wound for more than one circle for easy operation. The winding diameter corresponding to the crack-free state is the flexibility of the electrode sheet; the winding results are as follows Figure 1 As shown, the upper side is a real picture of the pole piece in a crack-free state, and the lower side is a real picture of the pole piece in a cracked state.

[0049] When using a glass rod with a larger diameter, in order to prevent the positive electrode sheet within the circumference of the glass rod after winding it once, which would cause waste, the positive electrode sheet is folded in a small area before formally winding the glass rod. If the area where the cracks are generated on the fold is small in the direction perpendicular to the fold, a glass rod with a smaller diameter is selected; if the area where the cracks are generated on the fold is large in the direction perpendicular to the fold, a glass rod with a larger diameter is directly selected to avoid continuous cracks in the process of gradually increasing the diameter of the glass rod when starting from a small diameter glass rod, resulting in a large amount of positive electrode sheets being wasted.

[0050] Among them, the compaction density tested was 2.2~2.6g / cm 3 The corresponding electrode flexibility is different due to the different main material types, surface density and compaction of the electrode. The measurement range of the compaction density can be flexibly adjusted according to actual conditions.

[0051] The above-mentioned battery electrode sheet is used as the positive electrode sheet, and the negative electrode sheet prepared separately is assembled, baked, injected, formed and divided into different volumes to form a wound battery cell;

[0052] Among them, the negative electrode plate includes a negative electrode current collector, and negative electrode active material layers are respectively provided on the two surfaces of the negative electrode current collector. The raw materials for preparing the negative electrode active material, etc. include graphite, conductive agent and binder with a mass ratio of 96:1:3. The preparation method is: graphite, conductive agent, binder and water are made into a slurry through a slurry mixing process, applied to the current collector, and baked to form a negative electrode plate. The raw materials and preparation methods of the negative electrode plates used in each wound battery cell are the same.

[0053] The prepared wound battery cells were tested, including energy density, constant current charging ratio and cycle capacity retention rate.

[0054] Energy density refers to the ratio of the energy released when the battery is discharged to 2.5V at 0.33C to the mass of the battery.

[0055] The constant current charging ratio refers to the percentage of constant current charging capacity to the total charging capacity when the battery cell is charged to 3.65V with constant current and constant voltage.

[0056] The cycle capacity retention rate refers to: after the lithium-ion battery is charged and discharged at a maximum voltage of 3.65V at 1C / 1C once, the battery discharge capacity at this time is C0, and then after 700 times of 1C / 1C charge and discharge at room temperature, the battery discharge capacity at this time is C1. The cycle capacity retention rate = (C1 / C0)*100%.

[0057] Since the electrical performance of the battery is mainly related to the positive electrode sheet, and the negative electrode sheet of the battery rarely breaks, the sheet flexibility and compaction density in this embodiment refer to the performance of the positive electrode sheet. The test results are shown in Table 1.

[0058] Table 1

[0059]

[0060] The product of the compaction density and the flexibility of the battery electrode is calculated, and the corresponding relationship between the product and the electrical performance (including energy density, 2C constant current ratio and capacity retention rate after 700 cycles of normal temperature cycling) is obtained. The results are shown in Table 1. It can be seen from Table 1 that as the surface density and compaction density continue to increase, the brittleness increases, and the flexibility of the electrode increases. The value increases accordingly. Appropriate compaction and toughness can ensure the processing yield of the electrode and the energy density of the battery. This is because: when the compaction density is low, although the toughness is good, the particle compaction is not tight enough, and the material advantages are not fully utilized. When the compaction density is too high, although the energy density is improved, the brittleness of the electrode will also increase, and the process processing and short-term performance will deteriorate. Therefore, through the above test, the flexibility of the electrode can be quantified, and the optimal compaction parameters can be output, which can improve the production yield and battery performance, reduce R&D costs, and improve production efficiency.

[0061] After processing the data in Table 1, the scatter plot is as follows Figure 2 As shown, it can be seen that the performance of the material is related to the flexibility and compaction density of the processed electrode. By evaluating the energy density, 2C constant current charging ratio and cycle capacity retention rate of the battery cell, it is concluded that the three performances are related to the product value. Therefore, in order to obtain the target electrical performance, it is necessary to select the product value within the appropriate reference range according to the technical requirements.

[0062] The relationship between energy density y and product x satisfies: y = 0.03x 2 +0.42x+159.5;

[0063] The relationship between the 2C charging constant current ratio z and the product x satisfies: z = -0.006x 2 +0.07x+98;

[0064] When the product value is ≥7.5, it can be found that as the product gradually increases, the cycle performance of the battery becomes worse and worse. The relationship between the capacity retention rate F(x) after 700 cycles at room temperature and the product x satisfies: F(x) = -0.02x 3 +0.35x 2 -1.8x+100.

[0065] This appropriate range is determined by the upper and lower limits of the product value. In actual production, the product value range is often It is believed that the performance of the electrode meets the requirements at this time, the battery cell can be wound and prepared, and the overall performance of the battery cell is relatively excellent.

[0066] It can be seen that the broader the target electrical performance requirements, the larger the upper and lower limits of the product value; the more stringent the target electrical performance requirements, the smaller the upper and lower limits of the product value.

[0067] In addition, when the product range is greater than 7.5, it is considered difficult to prepare a wound battery cell, and a stacked battery cell needs to be prepared to prevent the battery cell performance from being too low.

[0068] Based on the linear relationship between the three, at the beginning of the design, the parameter range of electrical performance such as cycle / energy density / 2C constant current charging ratio is locked according to performance requirements, thereby reducing the number of test groups and saving time and materials.

[0069] In addition, the flexibility of the positive electrode sheets within the set coating surface density range and the set compaction density range was tested, and all the sheets were prepared into wound cells. After the electrical performance was measured, the wound cells were disassembled and the crack state on the surface of the sheet was observed. The observation results included Figure 1 There are two cases in the figure: the upper side is a real picture of the electrode in a crack-free state, and the lower side is a real picture of the electrode in a cracked state. The statistical results of the sample states with electrode flexibility as a single variable are shown in Table 2: after the value of the electrode flexibility exceeds the adjacent critical value (the critical value in Table 2 is 3), the risk of electrode fracture increases significantly, indicating that the electrode flexibility can be used to evaluate the internal damage of the wound battery cell during service. Therefore, in order to avoid internal damage to the battery cell during service, technicians need to adjust the preparation process parameters to adjust the electrode flexibility to below the critical value.

[0070] Table 2

[0071]

[0072] Example 2

[0073] A system for implementing the method for evaluating battery performance using pole piece flexibility in Example 1 includes:

[0074] A first calculation module is used to obtain the electrode flexibility of a battery electrode with a set compaction density;

[0075] The second calculation module is used to obtain the electrical performance of the battery electrode after being processed into a battery cell;

[0076] The third calculation module is used to calculate the product of the compaction density of the battery electrode and the flexibility of the electrode, and obtain a corresponding relationship table of the electrical performance of the product;

[0077] The fourth calculation module is used to calculate the product of the flexibility and compaction density of the electrode with unknown electrical properties, and obtain the electrical properties of the battery prepared by the electrode with unknown electrical properties according to the corresponding relationship table.

[0078] The electrical properties in the second module include energy density, constant current charging ratio and cycle capacity retention rate.

[0079] Example 3

[0080] An electronic device comprises: a memory, a processor, and a program or instruction stored in the memory and executable on the processor, wherein the program or instruction, when executed by the processor, implements the steps of the method for evaluating battery performance using electrode flexibility in Example 1.

[0081] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for evaluating battery performance using electrode flexibility, characterized in that: The following steps are involved: S1. Winding battery pole pieces with different set compaction densities to obtain a winding diameter corresponding to a crack-free state as the pole piece flexibility; S2. Process all the battery electrodes without cracks in S1 into battery cells and test their electrical properties respectively; S3. Calculate the product of the compaction density and the flexibility of the battery electrode, and obtain a corresponding relationship table between the product and the electrical properties in S2; S4. Measure the flexibility and compaction density of the electrode with unknown electrical properties and calculate the product. Query the relationship table obtained in S3 for the electrical properties within the corresponding range of the product value, and use this as the electrical properties of the battery prepared from the electrode with unknown electrical properties.

2. The method for evaluating battery performance using electrode flexibility according to claim 1, wherein: In S1, the winding method is: winding the battery electrode closely around a rod-shaped mold of different set sizes for one or more times; Before winding, fold the battery electrode in half and select the diameter of the rod-shaped mold based on the width of the crack area at the fold position.

3. The method for evaluating battery performance using electrode flexibility according to claim 1, wherein: In S2, the electrical properties include: energy density, constant current charging ratio and cycle capacity retention rate.

4. The method for evaluating battery performance using electrode flexibility according to claim 3, wherein: Energy density refers to the ratio of the energy released by the battery to the mass of the battery when it is discharged to a set voltage.

5. The method for evaluating battery performance using electrode flexibility according to claim 3, wherein: The constant current charging ratio refers to the percentage of constant current charging capacity to the total charging capacity when the battery cell is charged to the set voltage using constant current and constant voltage.

6. The method for evaluating battery performance using electrode flexibility according to claim 3, wherein: The method for obtaining the cycle capacity retention rate is: after charging and discharging the battery at a set voltage of 1C / 1C once, the battery discharge capacity at this time is obtained as C0, and then after charging and discharging at a set number of 1C / 1C under normal temperature conditions, the battery discharge capacity at this time is obtained as C1. The cycle capacity retention rate = (C1 / C0)*100%.

7. The method for evaluating battery performance using electrode flexibility according to claim 1, wherein: The relational table in S3 is a two-dimensional table; Alternatively, in S4, the compaction density is the mass of the electrode coating per unit volume on the electrode sheet after rolling and drying.

8. A system for implementing the method for evaluating battery performance using electrode flexibility as described in any one of claims 1 to 7, characterized in that: include: A first calculation module is used to obtain the electrode flexibility of a battery electrode with a set compaction density; The second calculation module is used to obtain the electrical performance of the battery electrode after being processed into a battery cell; The third calculation module is used to calculate the product of the compaction density of the battery electrode and the flexibility of the electrode, and obtain a corresponding relationship table of the electrical performance of the product; The fourth calculation module is used to calculate the product of the flexibility and compaction density of the electrode with unknown electrical properties, and obtain the electrical properties of the battery prepared by the electrode with unknown electrical properties according to the corresponding relationship table.

9. The system according to claim 8, wherein The electrical properties include energy density, constant current charging ratio and cycle capacity retention rate.

10. An electronic device, characterized in that: include: A memory, a processor, and a program or instruction stored in the memory and executable on the processor, wherein the program or instruction, when executed by the processor, implements the steps in the method for evaluating battery performance using electrode flexibility as described in any one of claims 1 to 8.

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