Evaluation method for cycle performance of battery, battery and electric equipment

Abstract

The invention discloses a battery cycle performance evaluation method, a battery and electric equipment, and relates to the technical field of batteries, the method comprises the following steps: setting at least two test groups, each test group comprising at least two cells; numbering the battery cells in each test group, wherein different numbers correspond to different cycle tests; testing and recording the negative electrode particle size distribution of the corresponding battery cell in the empty electricity state after different cycle tests to obtain D50 data; recording and comparing the data of each test group; evaluating the cycle performance of the battery cells of different test groups; the battery cells in different test groups adopt different negative electrode materials, and other battery cell parameters and test environments are the same. According to the method, the cycle performance of the battery cell can be qualitatively evaluated through cycle testing of multiple groups of battery cells and increase of the negative electrode material D50, the time for evaluating the cycle performance of the battery cell is greatly shortened, and the research and development efficiency is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for evaluating battery cycle performance, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries currently dominate the market. According to their application areas, lithium-ion batteries can be divided into three categories: consumer batteries, power batteries, and energy storage batteries. The main feature of consumer batteries is their high energy density, which means that the battery can store more energy in the smallest possible volume to meet the needs of portable electronic devices. Power batteries focus on fast charging performance, and their goal is to complete the battery replenishment process in a very short time to adapt to application scenarios such as electric vehicles that have high requirements for charging speed. Energy storage batteries pay more attention to cycle performance, that is, the battery can still maintain a high capacity retention rate after multiple charge and discharge cycles. The mainstream 300+Ah large-capacity batteries on the market usually need to achieve a cycle life of 8,000 to 12,000 cycles at low rates to meet the needs of large-scale energy storage systems.

[0003] The energy density of the battery can be calculated through a series of simple charge and discharge tests, which can provide the charge and discharge performance data of the battery under specific conditions. The fast charging performance can be verified by designing a specific gradient lithium precipitation test to verify the lithium precipitation window of the battery, thereby determining its fast charging capability. Both energy density and fast charging performance can be evaluated through a series of short-term tests. However, the cycle performance of the battery needs to be determined through more complex tests. This usually involves subjecting the battery to long-term charge and discharge cycles under specific test conditions (for example: 25°C, 1C / 1C charge and discharge rate), recording the capacity retention rate of each cycle, and drawing a relationship curve between Cycle Index (number of cycles) and CapacityRetention (capacity retention rate). In this way, the cycle life of the battery in actual applications can be predicted, thereby providing more comprehensive and accurate data support for the performance evaluation of the battery.

[0004] However, drawing the Cycle Index (number of cycles)-Capacity Retention (capacity retention rate) curve to predict the cycle life requires a large number of data points. The battery needs to be subjected to long-term charge and discharge tests. Cycling 1,000 times at 1C takes nearly three months, and the R&D efficiency is low. Summary of the invention

[0005] The present application provides a battery cycle performance evaluation method, a battery and an electrical device, which can perform a qualitative evaluation of the battery cell cycle performance through the growth of the negative electrode material D50 by cycle testing of multiple groups of battery cells, thereby greatly shortening the time for evaluating the battery cell cycle performance and improving research and development efficiency.

[0006] In a first aspect, the present application provides a method for evaluating battery cycle performance, the method comprising the following steps:

[0007] At least two test groups are provided, each test group including at least two battery cells.

[0008] The cells in each test group are numbered, and different numbers correspond to different cycle tests.

[0009] After testing and recording different cycle tests, the negative electrode particle size distribution corresponding to the empty and charged state of the battery cell is obtained to obtain the D50 data.

[0010] The data from each test group were recorded and compared.

[0011] Evaluate the cell cycle performance of different test groups.

[0012] Different test groups use different negative electrode materials for the cells, but the other cell parameters and test environment are the same. This ensures the accuracy of the evaluation results and avoids interference from other factors.

[0013] The above steps can be used to qualitatively evaluate the cell cycle performance by observing the growth of the negative electrode material D50 through this multi-cell cycle test method. This method greatly shortens the time required to evaluate the cell cycle performance, thereby improving R&D efficiency. Through rapid evaluation, researchers can more quickly screen out cell materials with excellent performance and accelerate the development of battery technology.

[0014] In some examples, after recording and comparing the data of each test group, a curve graph of cycle number-capacity retention rate is drawn, and the expected cycle life of the battery cell is quantitatively analyzed through the curve graph of cycle number-capacity retention rate.

[0015] The above steps record the data of each test group in detail and conduct comparative analysis. Subsequently, based on these data, a relationship curve diagram between the number of cycles and the capacity retention rate of multiple groups of battery cells is drawn. Through the curve diagrams of these cycle numbers and capacity retention rates, quantitative analysis can be performed to accurately predict the expected cycle life of the battery cells. In the prior art, in order to draw a curve diagram between Cycle Index (number of cycles) and Capacity Retention (capacity retention rate) to predict the cycle life, a large number of data points are usually required. This means that the battery must be subjected to a long-term charge and discharge test, such as 1000 cycles at a rate of 1C, which usually takes nearly 3 months. Obviously, this long testing process leads to relatively low R&D efficiency. In contrast, the test method proposed in this application can significantly improve the test efficiency, thereby greatly improving the R&D efficiency.

[0016] In some examples, the test group includes a baseline group and at least one evaluation group, and the baseline group is used to compare the cycle performance of the evaluation group.

[0017] It is very important to test the battery cycle performance. The test of this application usually includes a set of benchmark groups and at least one evaluation group. The role of the benchmark group is to provide a reference standard so that the performance of the evaluation group in terms of cycle performance can be compared and detected. In this way, the performance differences of different batteries or battery packs during the cycle use process can be more accurately evaluated, thereby providing strong data support for the improvement and optimization of the battery.

[0018] In some examples, the test groups include two test groups, namely test group A and test group B. There are six battery cells in test group A and they are numbered A1, A2, A3, A4, A5, and A6. There are six battery cells in test group B and they are numbered B1, B2, B3, B4, B5, and B6. Battery cells with the same numbers have the same cycle test.

[0019] The above steps can realize the step-by-step cycle test of the battery cell, and then further perform a qualitative evaluation of the battery cell cycle performance through the growth of the negative electrode material D50, which greatly shortens the time for evaluating the battery cell cycle performance and improves R&D efficiency.

[0020] In some examples, the number of cycles of battery cell A1 and battery cell B1 is zero, the D50 data of the negative electrode material of battery cell A1 is 14.18 μm, and the D50 data of the negative electrode material of B1 is 10.35 μm.

[0021] The number of cycles of battery cell A2 and battery cell B2 is 100 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A2 is 15.21μm, and the D50 data of the negative electrode material of B2 is 11.29μm.

[0022] The number of cycles of battery cell A3 and battery cell B3 is 200 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A3 is 15.59 μm, and the D50 data of the negative electrode material of B3 is 11.61 μm.

[0023] The number of cycles of battery cell A4 and battery cell B4 is 300 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A4 is 15.67μm, and the D50 data of the negative electrode material of B4 is 12.07μm.

[0024] The number of cycles of battery cell A5 and battery cell B5 is 400 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A5 is 16.56μm, and the D50 data of the negative electrode material of B5 is 12.33μm.

[0025] The growth rate of the negative electrode material D50 in the B test group is lower than that in the A test group, and the cycle performance of the B test group is higher than that of the A test group.

[0026] The cycle numbers of both cell A1 and cell B1 are zero, which means they have not yet undergone any charge and discharge cycles. In this case, the D50 data of the negative electrode material of cell A1 is 14.18 microns, while the D50 data of the negative electrode material of cell B1 is 10.35 microns.

[0027] The cycle times of cell A2 and cell B2 are both 100, which means they have undergone 100 charge and discharge cycles, and the charge and discharge rate is 0.5 C. Under this condition, the D50 data of the negative electrode material of cell A2 is 15.21 microns, while the D50 data of the negative electrode material of cell B2 is 11.29 microns.

[0028] Furthermore, the number of cycles of the battery cell A3 and the battery cell B3 are both 200 times, and the charge and discharge rate is also 0.5 C. In this case, the D50 data of the negative electrode material of the battery cell A3 is 15.59 microns, while the D50 data of the negative electrode material of the battery cell B3 is 11.61 microns.

[0029] Cell A4 and cell B4 have 300 cycles and the charge and discharge rate is still 0.5C. Under this condition, the D50 data of the negative electrode material of cell A4 is 15.67 microns, while the D50 data of the negative electrode material of cell B4 is 12.07 microns.

[0030] The number of cycles of cell A5 and cell B5 is 400, and the charge and discharge rate remains at 0.5 C. In this case, the D50 data of the negative electrode material of cell A5 is 16.56 microns, while the D50 data of the negative electrode material of cell B5 is 12.33 microns.

[0031] By comparing these data, it can be found that in the B test group, the growth rate of the negative electrode material D50 is significantly lower than the growth rate of the negative electrode material D50 in the A test group. This result shows that the cycle performance of the B test group is significantly higher than that of the A test group.

[0032] In some examples, some test groups are provided with at least one verification cell, the number of cycles of the verification cell is greater than or equal to 1000 times, and the verification cell is used to detect the data accuracy of the corresponding test group.

[0033] The test group contains at least one verification cell. The number of cycles of these verification cells is set to be greater than or equal to 1000 times so that their performance stability can be fully evaluated. The main function of the verification cell is to ensure the accuracy and reliability of the test data, thereby verifying the authenticity of the evaluation method. In the early stages of the experiment, researchers will conduct detailed tests on the verification cells to ensure the effectiveness of the evaluation method. Once the test results of the verification cell show that the evaluation method is reliable, researchers can choose not to use the verification cell in subsequent experiments to save time and resources. However, if a large deviation or anomaly is found in the data in subsequent experiments, the researchers will re-enable the verification cell to ensure that the evaluation method is still valid and further verify and calibrate the data. In this way, the verification cell not only plays a key verification role in the early stages of the experiment, but also plays an important monitoring and calibration role during the experiment, ensuring the accuracy and reliability of the entire experimental process.

[0034] In some examples, the test parameters of the method include:

[0035] The test environment of the battery cell is 25℃.

[0036] And / or, the battery cell is charged and discharged at a constant current of 0.5C until the battery voltage reaches 3.65V.

[0037] And / or, the battery cell is charged in constant voltage mode until the charging current drops to 0.05C.

[0038] And / or, the battery cell is discharged at a constant current of 0.5C until the battery voltage drops to 2.5V.

[0039] The test environment of the evaluation method disclosed above is specifically: the test environment of the battery cell is set to a constant temperature of 25°C. During the test, the battery cell will be charged and discharged at a constant current of 0.5C, and this process will continue until the battery voltage reaches 3.65V. The battery cell is charged in a constant voltage mode, and this mode will continue until the charging current gradually decreases to a level of 0.05C. The battery cell will also be discharged at a constant current of 0.5C, and this discharge process will continue until the battery voltage drops to 2.5V.

[0040] In some examples, the particle size distribution of the negative electrode in the empty state of the battery cell is detected by a laser particle size analyzer.

[0041] The laser particle size analyzer is used to detect and analyze the particle size distribution of the negative electrode material in the fully discharged state of the battery cell. This detection method can reveal the size distribution characteristics of the negative electrode particles in detail, thereby providing important data support for the optimization and improvement of battery performance. Through this precise measurement method, scientists can better understand the physical properties of the battery cell in the empty state, and then adjust the battery design and manufacturing process to achieve the purpose of improving battery performance and life.

[0042] In a second aspect, the present application provides a battery, in which the battery cells are evaluated using the above-mentioned battery cycle performance evaluation method.

[0043] The battery cells evaluated by the above battery cycle performance evaluation method can have a shorter detection time and reduce the overall production cost of the battery. Specifically, through this multi-group battery cell cycle test method, by observing the growth of the negative electrode material D50, a qualitative evaluation of the battery cell cycle performance can be performed. This method greatly shortens the time required to evaluate the battery cell cycle performance, thereby improving research and development efficiency. Through rapid evaluation, researchers can more quickly screen out battery cell materials with excellent performance and accelerate the research and development process of battery technology.

[0044] In a third aspect, the present application provides an electrical device, including a battery and a device body as described above, wherein the battery is installed in the device body.

[0045] The battery cells evaluated by the above battery cycle performance evaluation method can have a shorter detection time, reduce the overall production cost of the battery, and thus reduce the cost of electrical equipment. Specifically, through this multi-group battery cell cycle test method, by observing the growth of the negative electrode material D50, a qualitative evaluation of the battery cell cycle performance can be performed. This method greatly shortens the time required to evaluate the battery cell cycle performance, thereby improving research and development efficiency. Through rapid evaluation, researchers can more quickly screen out battery cell materials with excellent performance and accelerate the research and development process of battery technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the present application or the prior art, the drawings required for use in the examples or prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some examples of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0047] Figure 1 It is a structural schematic diagram of a method for evaluating battery cycle performance in an example of the present application.

[0048] Figure 2 1 is a curve diagram showing the relationship between the number of battery cell cycles and the negative electrode D50 value in an example of the present application.

[0049] Figure 3 This is a curve diagram showing the relationship between the number of battery cell cycles and the battery cell capacity retention rate in an example of the present application. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and examples. It should be understood that the specific examples described here are only used to explain the present application and are not used to limit the present application.

[0051] To solve the above technical problems, please refer to Figure 1-Figure 3 As shown, the first aspect of the present application proposes a method for evaluating battery cycle performance, which can perform qualitative evaluation of battery cell cycle performance through cycle tests of multiple groups of battery cells and the growth of negative electrode material D50, thereby greatly shortening the time for evaluating battery cell cycle performance and improving R&D efficiency.

[0052] Reference Figure 1 In some examples, the present application provides a method for evaluating battery cycle performance, the method comprising the following steps:

[0053] Step S100: setting at least two test groups, each test group including at least two battery cells.

[0054] In the above steps, at least two test groups may be set, each test group including at least two battery cells. These battery cells will be used in subsequent cycle tests for comparison and evaluation.

[0055] Step S200: numbering the cells in each test group, with different numbers corresponding to different cycle tests.

[0056] In the above steps, the cells in each test group can be numbered to ensure that each number corresponds to a specific cycle test. In this way, the performance of different cells in different cycle tests can be distinguished.

[0057] Step S300: After testing and recording different cycle tests, the particle size distribution of the negative electrode corresponding to the empty state of the battery cell is obtained to obtain D50 data.

[0058] In the above steps, the battery cells in each test group can be cycled and the negative electrode particle size distribution of the corresponding battery cells in the empty state after different cycle tests can be recorded. By measuring and recording these data, the D50 data of each battery cell can be obtained, that is, the median of the negative electrode particle size distribution.

[0059] Step S400: Record and compare the data of each test group.

[0060] In the above steps, the data of each test group can be recorded in detail and compared and analyzed. By comparing the data of different test groups, the performance differences of different batteries in the cycle test can be found.

[0061] Step S500: Evaluate the cycling performance of cells in different test groups.

[0062] In the above steps, the cycle performance of the cells in different test groups can be evaluated based on the results of the comparative analysis. In this way, it is possible to quickly identify which cells have better cycle performance.

[0063] Different test groups use different negative electrode materials for the cells, but the other cell parameters and test environment are the same. This ensures the accuracy of the evaluation results and avoids interference from other factors.

[0064] Through this multi-cell cycle test method, the cell cycle performance can be qualitatively evaluated by observing the growth of the negative electrode material D50. This method greatly shortens the time required to evaluate the cell cycle performance, thereby improving R&D efficiency. Through rapid evaluation, researchers can more quickly screen out cell materials with excellent performance and accelerate the development of battery technology.

[0065] Reference Figure 2 By executing the above steps, a relationship curve between the number of cycles and the D50 value of multiple groups of battery cells can be drawn. Such a chart can more intuitively analyze and predict the cycle life of the battery cell, thereby providing an important reference for the battery management system. By observing these curves, the performance change trend of the battery cell at different cycle numbers can be identified, and then its reliability and durability in practical applications can be evaluated. This visualization method not only helps to better understand the aging process of the battery cell, but also provides strong data support for battery design and optimization.

[0066] Reference Figure 3In some examples, after recording and comparing the data of each test group, a curve chart of the number of cycles-capacity retention rate of multiple groups of battery cells is drawn, and the expected cycle life of the battery cells is quantitatively analyzed through the curve chart of the number of cycles-capacity retention rate.

[0067] The above steps record the data of each test group in detail and conduct comparative analysis. Subsequently, based on these data, a relationship curve diagram between the number of cycles and the capacity retention rate of multiple groups of battery cells is drawn. Through the curve diagrams of these cycle numbers and capacity retention rates, quantitative analysis can be performed to accurately predict the expected cycle life of the battery cells. In the prior art, in order to draw a curve diagram between Cycle Index (number of cycles) and Capacity Retention (capacity retention rate) to predict the cycle life, a large number of data points are usually required. This means that the battery must be subjected to a long-term charge and discharge test, such as 1000 cycles at a rate of 1C, which usually takes nearly 3 months. Obviously, this long testing process leads to relatively low R&D efficiency. In contrast, the test method proposed in this application can significantly improve the test efficiency, thereby greatly improving the R&D efficiency.

[0068] The "Cycle Index-Capacity Retention Curve" usually refers to a graph used in the field of battery research to describe the battery's charge and discharge cycle performance. On this curve, the horizontal axis represents the number of battery charge and discharge cycles (i.e., the cycle index, Cycle Index), and the vertical axis represents the battery capacity retention rate or retention rate (i.e., capacity retention, Capacity Retention). Through this curve, it can be observed whether the battery capacity decreases as the number of charge and discharge times increases, and how fast it decreases, thereby evaluating the battery's life and performance stability.

[0069] In some examples, the test group includes a baseline group and at least one evaluation group, and the baseline group is used to compare the cycle performance of the evaluation group.

[0070] It is very important to test the battery cycle performance. The test of this application usually includes a set of benchmark groups and at least one evaluation group. The role of the benchmark group is to provide a reference standard so that the performance of the evaluation group in terms of cycle performance can be compared and detected. In this way, the performance differences of different batteries or battery packs during the cycle use process can be more accurately evaluated, thereby providing strong data support for the improvement and optimization of the battery.

[0071] In some examples, the test groups include two test groups, namely test group A and test group B. There are six battery cells in test group A and they are numbered A1, A2, A3, A4, A5, and A6. There are six battery cells in test group B and they are numbered B1, B2, B3, B4, B5, and B6. Battery cells with the same numbers have the same cycle test.

[0072] The above steps can realize the step-by-step cycle test of the battery cell, and then further perform a qualitative evaluation of the battery cell cycle performance through the growth of the negative electrode material D50, which greatly shortens the time for evaluating the battery cell cycle performance and improves R&D efficiency.

[0073] For this test, the test group is designed to contain two main parts, which are called A test group and B test group. In the A test group, six cells are set, which are numbered A1, A2, A3, A4, A5 and A6. Similarly, in the B test group, six cells are set, which are numbered B1, B2, B3, B4, B5 and B6. It is worth noting that the cells with the same number in the number will undergo the same test procedures in the cycle test.

[0074] Through the above steps, a step-by-step cycle test of the battery cell can be achieved. This test method can effectively qualitatively evaluate the cycle performance of the battery cell by observing the growth of the negative electrode material D50. This method not only greatly shortens the time required to evaluate the cycle performance of the battery cell, but also significantly improves the efficiency of the research and development process. In this way, the R&D team can identify high-performance batteries more quickly, thereby accelerating the development and optimization of battery technology.

[0075] In some examples, the number of cycles of battery cell A1 and battery cell B1 is zero, the D50 data of the negative electrode material of battery cell A1 is 14.18 μm, and the D50 data of the negative electrode material of B1 is 10.35 μm.

[0076] The number of cycles of battery cell A2 and battery cell B2 is 100 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A2 is 15.21μm, and the D50 data of the negative electrode material of B2 is 11.29μm.

[0077] The number of cycles of battery cell A3 and battery cell B3 is 200 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A3 is 15.59 μm, and the D50 data of the negative electrode material of B3 is 11.61 μm.

[0078] The number of cycles of battery cell A4 and battery cell B4 is 300 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A4 is 15.67μm, and the D50 data of the negative electrode material of B4 is 12.07μm.

[0079] The number of cycles of battery cell A5 and battery cell B5 is 400 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery cell A5 is 16.56μm, and the D50 data of the negative electrode material of B5 is 12.33μm.

[0080] The growth rate of the negative electrode material D50 in the B test group is lower than that in the A test group, and the cycle performance of the B test group is higher than that of the A test group.

[0081] The cycle numbers of both cell A1 and cell B1 are zero, which means they have not yet undergone any charge and discharge cycles. In this case, the D50 data of the negative electrode material of cell A1 is 14.18 microns, while the D50 data of the negative electrode material of cell B1 is 10.35 microns.

[0082] The cycle times of cell A2 and cell B2 are both 100, which means they have undergone 100 charge and discharge cycles, and the charge and discharge rate is 0.5 C. Under this condition, the D50 data of the negative electrode material of cell A2 is 15.21 microns, while the D50 data of the negative electrode material of cell B2 is 11.29 microns.

[0083] Furthermore, the number of cycles of the battery cell A3 and the battery cell B3 are both 200 times, and the charge and discharge rate is also 0.5 C. In this case, the D50 data of the negative electrode material of the battery cell A3 is 15.59 microns, while the D50 data of the negative electrode material of the battery cell B3 is 11.61 microns.

[0084] Cell A4 and cell B4 have 300 cycles and the charge and discharge rate is still 0.5C. Under this condition, the D50 data of the negative electrode material of cell A4 is 15.67 microns, while the D50 data of the negative electrode material of cell B4 is 12.07 microns.

[0085] The number of cycles of cell A5 and cell B5 is 400, and the charge and discharge rate remains at 0.5 C. In this case, the D50 data of the negative electrode material of cell A5 is 16.56 microns, while the D50 data of the negative electrode material of cell B5 is 12.33 microns.

[0086] By comparing these data, it can be found that in the B test group, the growth rate of the negative electrode material D50 is significantly lower than the growth rate of the negative electrode material D50 in the A test group. This result shows that the cycle performance of the B test group is significantly higher than that of the A test group.

[0087] Please refer to Table 1 and Table 2 below for details:

[0088] Test samples Cycle D50(μm) A1 Before loop 14.18 A2 0.5C 100cls 15.21 A3 0.5C 200cls 15.59 A4 0.5C 300cls 15.67 A5 0.5C 500cls 16.56

[0089] Table 1 Negative electrode D50 of group A cells after different cycles

[0090] Table 1 records the D50 values ​​of the negative electrode particles of the A battery cell after different cycles. D50 refers to the average particle size when the cumulative distribution in the particle group reaches 50%, which is an important parameter for measuring the particle size distribution. In this table, the unit of D50 is micrometer (μm). The test sample A1 is in its original state before the cycle, and its D50 value is 14.18 micrometers; as the cycle increases, the D50 values ​​of A2, A3, A4 and A5 gradually increase, reaching 15.21 micrometers, 15.59 micrometers, 15.67 micrometers and 16.56 micrometers respectively.

[0091] This indicates that the average particle size of the negative electrode particles increases with the charge and discharge cycle of the battery cell.

[0092] Test samples Cycle D50(μm) B1 Before loop 10.35 B2 0.5C 100cls 11.29 B3 0.5C 200cls 11.61 B4 0.5C 300cls 12.07 B5 0.5C 500cls 12.33

[0093] Table 2 Negative electrode D50 of group B cells after different cycles

[0094] Table 2 shows the changes in the median diameter (D50) of the particle size distribution of the negative electrode material of the B battery after different cycles. D50 refers to the median diameter in the particle size distribution, that is, half of the particles are smaller than this value, and the other half are larger than this value. The test samples include B1 before cycling and B2 to B5 after different numbers of cycles. The cycle period uses "C" to represent the charging rate and "cls" to represent the number of cycles. It can be seen from the data that the D50 value gradually increases with the increase in the number of cycles, which indicates that the particle size of the negative electrode material increases during the cycle. This phenomenon may be due to a certain degree of agglomeration or breakage of the particles during the cycle, resulting in an increase in particle size.

[0095] By comparing the negative electrode D50 values ​​of cell A and cell B after different cycles, it can be found that with the increase in the number of cycles, the D50 values ​​of both cells show a trend of gradual increase. However, the D50 growth rate of cell B is lower than that of cell A, which indicates that during the cycle, the increase in the particle size of the negative electrode material of cell B is smaller. Further analysis shows that the regrowth rate of the SEI film of cell B during the cycle is lower than that of cell A, which means that the loss of active lithium in cell B is lower. Therefore, it can be concluded that the cycle performance of cell B is better than that of cell A.

[0096] In order to show this result more intuitively, we can draw a scatter plot with the cycle period of A cell and B cell as the X-axis and D50 as the Y-axis. Figure 2 By observing the growth rate of D50, the cycle performance of the battery cell can be evaluated. Figure 2As shown in the figure, the D50 growth rate of cell B is lower than that of cell A, which indicates that during the cycle, the SEI film regrowth rate of cell B is lower and the loss of active lithium is less. Therefore, the cycle performance of cell B is better than that of cell A.

[0097] The data shown above are for illustration and demonstration purposes only, and they do not mean that the methods or techniques described in this application are limited to the use of these specific test methods. These data reflect the performance of some specific negative electrode graphite materials during the test, and these values ​​are based on the negative electrode graphite materials currently used. If the composition or structure of the negative electrode graphite material changes, the corresponding test results and values ​​will also change and adjust accordingly. Therefore, these data are for reference only, and corresponding tests and adjustments need to be carried out according to specific circumstances in actual applications.

[0098] In some examples, some test groups are equipped with at least one verification cell, the number of cycles of the verification cell is greater than or equal to 1000 times, and the verification cell is used to detect the accuracy of the data of the corresponding test group. The verification cell is used to verify the authenticity of the evaluation method. The verification cell can be verified only in the initial experiment, and the verification cell can be omitted in subsequent tests. Alternatively, the verification cell is enabled after a large deviation occurs in the data.

[0099] The test group contains at least one verification cell. The number of cycles of these verification cells is set to be greater than or equal to 1000 times so that their performance stability can be fully evaluated. The main function of the verification cell is to ensure the accuracy and reliability of the test data, thereby verifying the authenticity of the evaluation method. In the early stages of the experiment, researchers will conduct detailed tests on the verification cells to ensure the effectiveness of the evaluation method. Once the test results of the verification cell show that the evaluation method is reliable, researchers can choose not to use the verification cell in subsequent experiments to save time and resources. However, if a large deviation or anomaly is found in the data in subsequent experiments, the researchers will re-enable the verification cell to ensure that the evaluation method is still valid and further verify and calibrate the data. In this way, the verification cell not only plays a key verification role in the early stages of the experiment, but also plays an important monitoring and calibration role during the experiment, ensuring the accuracy and reliability of the entire experimental process.

[0100] In some examples, the test parameters of the battery cycling performance evaluation method include:

[0101] The test environment of the battery cell is 25℃.

[0102] And / or, the battery cell is charged and discharged at a constant current of 0.5C until the battery voltage reaches 3.65V.

[0103] And / or, the battery cell is charged in constant voltage mode until the charging current drops to 0.05C.

[0104] And / or, the battery cell is discharged at a constant current of 0.5C until the battery voltage drops to 2.5V.

[0105] The test environment of the evaluation method disclosed above is specifically: the test environment of the battery cell is set to a constant temperature of 25°C. During the test, the battery cell will be charged and discharged at a constant current of 0.5C, and this process will continue until the battery voltage reaches 3.65V. The battery cell is charged in a constant voltage mode, and this mode will continue until the charging current gradually decreases to a level of 0.05C. The battery cell will also be discharged at a constant current of 0.5C, and this discharge process will continue until the battery voltage drops to 2.5V.

[0106] The above test parameters correspond to the attached Figure 3 Parameters in, specifically:

[0107] The 0.5C CC to 3.65V condition means that the battery is charged or discharged at a constant current (CC) of 0.5C until the battery voltage reaches 3.65 volts (V). In this mode, the battery will be charged or discharged at a constant current until the set voltage threshold is reached.

[0108] The CV to 0.05C condition means that the battery is charged in constant voltage (CV) mode until the charging current drops to 0.05C. In this mode, the battery is charged at a constant voltage until the charging current gradually decreases to the set current threshold.

[0109] The 0.5C DC to 2.5V condition means that the battery is discharged at a constant current of 0.5C until the battery voltage drops to 2.5 volts (V). In this mode, the battery is discharged at a constant current until the set voltage threshold is reached.

[0110] Through these detailed explanations, we can better understand the various test conditions and parameters used in the 25°C cycle performance test of LFP batteries. These test conditions help to evaluate the performance of the battery at different charge and discharge rates and voltage ranges.

[0111] In some examples, the particle size distribution of the negative electrode in the empty state of the battery cell is detected by a laser particle size analyzer.

[0112] The laser particle size analyzer is used to detect and analyze the particle size distribution of the negative electrode material in the fully discharged state of the battery cell. This detection method can reveal the size distribution characteristics of the negative electrode particles in detail, thereby providing important data support for the optimization and improvement of battery performance. Through this precise measurement method, scientists can better understand the physical properties of the battery cell in the empty state, and then adjust the battery design and manufacturing process to achieve the purpose of improving battery performance and life.

[0113] The present application proposes to evaluate the cycle performance of lithium-ion batteries through a series of short-term tests. This method is applicable to various types of lithium-ion batteries, including but not limited to soft-pack batteries, cylindrical batteries and square batteries. In the selection of positive electrode materials, this method covers widely used lithium-containing positive electrode materials, such as lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA) and lithium cobalt oxide (LCO). As for the negative electrode material, this method allows the use of graphite (Gr) or silicon-based materials, including one or more of silicon-oxygen or silicon-carbon composites. In the selection of electrolyte or auxiliary materials, any common product on the market can be used. In the manufacturing process of the battery, a lamination process or a winding process can be used, both of which are mature technologies widely used in the industry.

[0114] Among them, LFP, Lithium Iron Phosphate, Lithium Iron Phosphate. NCM, Lithium Nickel Cobalt Manganese Oxide, Lithium Nickel Cobalt Manganese Oxide. NCA, Lithium Nickel Cobalt Aluminum Oxide, Lithium Nickel Cobalt Aluminum Oxide. LCO, Lithium Cobalt Oxide, Lithium Cobalt Oxide. Gr, Graphite, Graphite. SP, Conductive Agent, Conductive Agent. PVDF, Polyvinylidene Fluoride, Polyvinylidene Fluoride. NMP, N-Methyl-2-pyrrolidone, N-methyl-2-pyrrolidone. CMC, Carboxymethyl Cellulose, Carboxymethyl Cellulose. SBR, Styrene Butadiene Rubber, Styrene Butadiene Rubber.

[0115] In this solution, the test cells used are all LFP-Gr soft-pack batteries with a capacity of 5Ah, which are manufactured by a lamination process. This application exemplarily discloses the following specific manufacturing steps:

[0116] Evenly mix lithium iron phosphate (LFP), conductive agent (SP) and binder (PVDF) in a mass ratio of 95.5:2.5:2. This ratio can be adjusted as needed. Usually, the ratio of LFP is greater than 80%, while the ratio of SP and PVDF is less than 10%. Then, add an appropriate amount of solvent N-methyl-2-pyrrolidone (NMP), whose solid content is usually between 50% and 80%, and the solid content in this example is 60%. After evenly mixing, the positive electrode slurry is obtained.

[0117] Graphite (Gr), conductive agent (SP), carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are uniformly mixed in a mass ratio of 96.2:0.8:1.2:1.8. Similarly, this ratio can be adjusted as needed. Usually, the ratio of Gr is greater than 80%, the ratio of SP is less than 10%, and the total ratio of CMC and SBR is less than 10%. Then, add an appropriate amount of deionized water, the solid content of which is usually between 40% and 70%, and the solid content in this case is 45%. After uniform mixing, the negative electrode slurry is obtained.

[0118] The prepared positive and negative electrode slurries are coated on aluminum foil and copper foil respectively, and dried to obtain positive and negative electrode sheets. In this example, the single-sided surface density of the positive electrode is 194.8g / m2, and the single-sided surface density of the negative electrode is 91.2g / m2. The surface density of the electrode sheet can be dynamically adjusted according to the battery design. Usually, the single-sided surface density of the positive electrode ranges from 150 to 300g / m2, and the single-sided surface density of the negative electrode ranges from 50 to 200g / m2.

[0119] The dried pole pieces are cold pressed to ensure that the compaction density of the positive pole piece reaches 2.55g / cm3 and the compaction density of the negative pole piece reaches 1.63g / cm3. The compaction density of the pole piece can also be dynamically adjusted according to the battery design. Usually, the compaction density of the positive pole piece ranges from 2.00 to 3.00g / cm3, and the compaction density of the negative pole piece ranges from 1.50g / cm3 to 1.80g / cm3.

[0120] The positive and negative electrode sheets that have been rolled are cut and cut to obtain the appropriate size of the electrode sheets. Subsequently, they are stacked in the order of packaging film / diaphragm / [negative electrode / diaphragm / positive electrode / diaphragm]×N / negative electrode / diaphragm / packaging film. The packaging film is usually made of aluminum-plastic film, and the value of N can be adjusted according to the battery capacity design. For soft-pack batteries, N is usually in the range of 1 to 50. After the stacking is completed, the battery is hot-pressed and the pole ears are welded on the positive and negative electrodes respectively.

[0121] After the battery is assembled, it needs to be placed in an oven and dried at 100 to 120°C for 12 to 24 hours to remove moisture from the positive and negative electrodes. After drying, the electrolyte is injected into the battery and the battery is sealed. After the battery has been processed through aging, formation, and capacity separation (0% SOC), the test batteries A1 to A6 and B1 to B6 are obtained. The difference between batteries A and B is that the negative electrode graphite materials used are different. Through these steps, the capacity decay and changes in active materials during the cycle of the battery can be evaluated.

[0122] Finally, the particle size distribution of the negative electrode in the empty state after different stages of the cycle was tested to obtain the D50 data, and the results are shown in Tables 1 and 2. Through these data, the cycle performance of lithium-ion batteries can be further analyzed and evaluated.

[0123] In a second aspect, the present application provides a battery, in which the battery cells are evaluated using the above-mentioned battery cycle performance evaluation method.

[0124] The battery cells evaluated by the above battery cycle performance evaluation method can have a shorter detection time and reduce the overall production cost of the battery. Specifically, through this multi-group battery cell cycle test method, by observing the growth of the negative electrode material D50, a qualitative evaluation of the battery cell cycle performance can be performed. This method greatly shortens the time required to evaluate the battery cell cycle performance, thereby improving research and development efficiency. Through rapid evaluation, researchers can more quickly screen out battery cell materials with excellent performance and accelerate the research and development process of battery technology.

[0125] In a third aspect, the present application provides an electrical device, including a battery and a device body as described above, wherein the battery is installed in the device body.

[0126] The battery cells evaluated by the above battery cycle performance evaluation method can have a shorter detection time, reduce the overall production cost of the battery, and thus reduce the cost of electrical equipment. Specifically, through this multi-group battery cell cycle test method, by observing the growth of the negative electrode material D50, a qualitative evaluation of the battery cell cycle performance can be performed. This method greatly shortens the time required to evaluate the battery cell cycle performance, thereby improving research and development efficiency. Through rapid evaluation, researchers can more quickly screen out battery cell materials with excellent performance and accelerate the research and development process of battery technology.

[0127] The same or similar numbers in the drawings of this application correspond to the same or similar parts; in the description of this application, it should be understood that if the terms "upper", "lower", "left", "right", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings. This is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as a limitation on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0128] The above are only preferred examples of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for evaluating battery cycle performance, characterized in that: The method comprises the following steps: Setting at least two test groups, each of the test groups comprising at least two battery cells; Numbering the cells in each test group, with different numbers corresponding to different cycle tests; After testing and recording different cycle tests, the particle size distribution of the negative electrode corresponding to the empty state of the battery cell is obtained to obtain the D50 data; Recording and comparing the data of each test group; Evaluate the cycling performance of the cells in the different test groups; The negative electrode materials used in the battery cells in different test groups are different, and the other battery cell parameters and test environment are the same.

2. The method for evaluating battery cycle performance according to claim 1, characterized in that: After recording and comparing the data of each test group, a curve graph of cycle number-capacity retention rate is drawn, and the expected cycle life of the battery cell is quantitatively analyzed through the curve graph of cycle number-capacity retention rate.

3. The method for evaluating battery cycle performance according to claim 1, wherein: The test group includes a reference group and at least one evaluation group, wherein the reference group is used for comparatively testing the cycle performance of the evaluation group.

4. The method for evaluating battery cycle performance according to claim 1, wherein: The test groups include two, which are test group A and test group B. There are six battery cells in test group A and they are numbered A1, A2, A3, A4, A5, and A6, and there are six battery cells in test group B and they are numbered B1, B2, B3, B4, B5, and B6. Battery cells with the same numbers undergo the same cycle test.

5. The method for evaluating battery cycle performance according to claim 4, characterized in that: The number of cycles of battery A1 and battery B1 is zero, the D50 data of the negative electrode material of battery A1 is 14.18μm, and the D50 data of the negative electrode material of B1 is 10.35μm; The number of cycles of battery A2 and battery B2 is 100 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery A2 is 15.21μm, and the D50 data of the negative electrode material of B2 is 11.29μm; The number of cycles of battery A3 and battery B3 is 200 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery A3 is 15.59μm, and the D50 data of the negative electrode material of B3 is 11.61μm; The number of cycles of battery A4 and battery B4 is 300 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery A4 is 15.67μm, and the D50 data of the negative electrode material of B4 is 12.07μm; The number of cycles of battery A5 and battery B5 is 400 times, and the charge and discharge rate is 0.5C. The D50 data of the negative electrode material of battery A5 is 16.56μm, and the D50 data of the negative electrode material of B5 is 12.33μm; The growth rate of the negative electrode material D50 in the B test group is lower than the growth rate of the negative electrode material D50 in the A test group, and the cycle performance of the B test group is higher than that of the A test group.

6. The method for evaluating battery cycle performance according to claim 1, wherein: Some of the test groups are provided with at least one verification cell, the number of cycles of the verification cell is greater than or equal to 1000 times, and the verification cell is used to detect the accuracy of the data corresponding to the test group.

7. The method for evaluating battery cycle performance according to any one of claims 1 to 6, characterized in that: The test parameters of the method include: The test environment of the battery cell is 25℃; and / or, the battery cell is charged and discharged at a constant current of 0.5C until the battery voltage reaches 3.65V; and / or, the battery cell is charged in constant voltage mode until the charging current drops to 0.05C; And / or, the battery cell is discharged at a constant current of 0.5C until the battery voltage drops to 2.5V.

8. The method for evaluating battery cycle performance according to claim 1, characterized in that: The particle size distribution of the negative electrode in the empty state of the battery cell is detected by a laser particle size analyzer.

9. A battery, characterized in that: The battery cells in the battery are evaluated by the battery cycle performance evaluation method described in claims 1 to 8.

10. An electrical device, characterized in that: include: A battery as claimed in claim 9; and, The device body is provided with the battery installed in the device body.

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