Method for testing safety performance of positive electrode material

Abstract

The invention provides a positive electrode material safety performance test method, and belongs to the technical field of secondary battery safety, and the test method comprises the following steps: a material packaging step: respectively assembling a plurality of groups of positive electrode materials into a battery cell; charging the plurality of battery cells to a set electric quantity; a test step: respectively carrying out acupuncture test on the battery cells under the same condition to obtain acupuncture test results of the battery cells; wherein the acupuncture test result comprises a data relationship between a stress value of the battery cell in the acupuncture process and test time; a data processing step: obtaining stress peak values and stress difference values of the plurality of battery cells according to the acupuncture test results of the plurality of battery cells; and a performance evaluation step: based on the stress peak values and the stress difference values of the plurality of battery cells, comparing and analyzing the safety performance of the plurality of groups of positive electrode materials. According to the test method disclosed by the invention, the external force resistance and the thermal stability of the positive electrode material are accurately evaluated according to the stress peak value and the stress difference value of the battery cell in the needling process.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery safety, and in particular to a method for testing the safety performance of a positive electrode material. Background Art

[0002] As the number of electric vehicles in the market increases, the safety of battery packs has also attracted more and more attention. The safety of battery cells is the basis of battery pack safety. There are a series of safety abuse tests at the cell level to simulate the safety of batteries under extreme abuse conditions. The most stringent test is the puncture test. The mechanism of cell puncture failure is that the diaphragm is punctured by a needle, resulting in contact between the positive and negative electrodes. The local large current causes the temperature of the electrode to rise rapidly to the failure temperature of the electrode, causing the battery cell to catch fire and explode.

[0003] In the needle penetration test, the thermal safety performance of the battery cell materials is usually evaluated by comparing the thermal failure temperature. The evaluation criteria for the safety performance of the positive electrode materials are relatively single, and it is unable to more accurately represent the reaction intensity of the battery cell materials during short-circuit thermal runaway, making it difficult to conduct a more detailed and accurate evaluation of the physical and chemical safety performance of the battery cell materials.

[0004] Therefore, it is necessary to design a positive electrode material safety performance testing method to solve the above problems. Summary of the invention

[0005] In view of the above shortcomings of the prior art, the present invention provides a method for testing the safety performance of positive electrode materials, which uses the peak force value and force differential value of the soft-pack battery cell during the needle puncture process to evaluate the external force resistance and thermal safety performance of the positive electrode material, thereby solving the technical problem that the existing needle puncture test only evaluates the thermal safety performance based on the thermal failure temperature and cannot more accurately evaluate the physical and chemical safety performance of the positive electrode material.

[0006] To achieve the above-mentioned purpose and other related purposes, the present invention provides a positive electrode material safety performance testing method, the testing method comprising:

[0007] Material packaging step: assembling multiple groups of positive electrode materials into battery cells respectively; charging the multiple battery cells to a set power;

[0008] Testing step: performing a needle puncture test on the battery cells respectively under the same conditions to obtain a needle puncture test result of each battery cell; wherein the needle puncture test result includes a data relationship between a force value and a test time of the battery cell during the needle puncture process;

[0009] Data processing step: obtaining force peak values ​​and force differential values ​​of the multiple battery cells according to the acupuncture test results of the multiple battery cells;

[0010] Performance evaluation step: based on the force peak values ​​and force differential values ​​of the multiple battery cells, comparing and analyzing the safety performance of the multiple groups of positive electrode materials.

[0011] In an example of the present invention, in the data processing step, the data processing of the puncture test result of each battery cell includes:

[0012] Based on the data relationship between the force value and the test time of the battery cell during the acupuncture process, the force value-time curve of the battery cell during the acupuncture process is obtained; based on the force value-time curve, the force peak value of the battery cell during the acupuncture process is obtained; the force value-time curve is differentially processed to obtain the force value differential curve of the battery cell; and the force differential value of the battery cell is obtained from the force value differential curve.

[0013] In an example of the present invention, performing differential processing on the force value-time curve to obtain the force value differential curve of the battery cell includes:

[0014] The data relationship between the slope value and the test time on the force value-time curve is obtained; and the force value difference curve of the battery cell is obtained according to the data relationship between the slope value and the test time.

[0015] In an example of the present invention, obtaining the force difference value of the battery cell from the force value difference curve includes:

[0016] The upper limit value and the lower limit value of the force value on the force value difference curve are intercepted; and the force difference value of the battery cell is obtained according to the upper limit value and the lower limit value of the force value.

[0017] In an example of the present invention, the performance evaluation step includes:

[0018] By comparing the force peak values ​​of the multiple battery cells, the external force resistance performance of the corresponding multiple groups of positive electrode materials is analyzed; by comparing the force differential values ​​of the multiple battery cells, the thermal stability performance of the corresponding multiple groups of positive electrode materials is analyzed.

[0019] In an example of the present invention, in the material packaging step, charging the plurality of battery cells to a set power level includes:

[0020] The plurality of battery cells are charged to the same set power using the same charging rate; wherein the charging rate is 0.1C to 5C.

[0021] In an example of the present invention, during the puncture test, a fixture is used to clamp the test needle, and the plurality of battery cells are punctured at the same puncture rate.

[0022] In one example of the present invention, the aperture of the fixture is 10 to 20 mm, the test needle is a steel needle or a ceramic needle, the diameter of the test needle is 5 to 10 mm, and the puncture rate is 50 to 100 mm / s.

[0023] In an example of the present invention, the puncture site of the testing needle on the battery cell is located at the center of the body of the battery cell.

[0024] In an example of the present invention, the test result also includes the data relationship between the voltage of the battery cell during the acupuncture process and the test time.

[0025] The testing method of the present invention utilizes the data relationship between the force value and the test time of the battery cell during the needle puncture test to obtain the peak force value and the force differential value of the battery cell during the needle puncture process, and the peak force value and the force differential value of the battery cell during the needle puncture process respectively reflect the external force resistance performance of the positive electrode material itself and the reaction intensity during short-circuit thermal runaway. Therefore, the testing method can accurately evaluate the external force resistance performance and thermal stability performance of the positive electrode material according to the peak force value and the force differential value of the battery cell during the needle puncture process, and plays a role in comprehensively evaluating the physical and chemical safety performance of the positive electrode material by collecting a single force value parameter of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 Schematic diagram of a process for testing the safety performance of positive electrode materials in one embodiment of the present invention;

[0028] Figure 2 This is a flow chart of step S3 in a method for testing the safety performance of a positive electrode material in one embodiment of the present invention;

[0029] Figure 3 This is a flow chart of step S4 in a method for testing the safety performance of a positive electrode material in one embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the acupuncture positions of a soft-pack battery cell in one embodiment of the present invention;

[0031] Figure 5 It is a force value / voltage-time curve diagram of the positive electrode material NCM811 in a needle puncture test in one embodiment of the present invention;

[0032] Figure 6A force value / voltage difference curve diagram of the positive electrode material NCM811 in a needle puncture test in one embodiment of the present invention;

[0033] Figure 7 This is a comparison diagram of the peak force of positive electrode materials NCM532, NCM712, NCM811 and LFP in a needle puncture test in one embodiment of the present invention;

[0034] Figure 8 This is a comparison chart of the force difference values ​​of positive electrode materials NCM532, NCM712, NCM811 and LFP in a needle penetration test in one embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] It should be noted that, in the absence of conflict, the features in the following examples and embodiments can be combined with each other. It should also be understood that the terms used in the examples of the present invention are intended to describe specific embodiments rather than to limit the scope of the present invention. The test methods in the following examples that do not specify specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0037] For simplicity, only some numerical ranges are explicitly disclosed herein, and each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unspecified range.

[0038] like Figure 1 As shown, the present invention provides a method for testing the safety performance of a positive electrode material, the testing method comprising the following steps:

[0039] S1, material packaging step: assembling multiple groups of positive electrode materials into battery cells respectively; charging the multiple battery cells to a set power;

[0040] S2, testing step: performing a needle puncture test on the battery cells respectively under the same conditions to obtain a needle puncture test result of each battery cell; wherein the needle puncture test result includes a data relationship between a force value and a test time of the battery cell during the needle puncture process;

[0041] S3, data processing step: according to the acupuncture test results of the plurality of battery cells, obtaining the force peak values ​​and force differential values ​​of the plurality of battery cells;

[0042] S4, performance evaluation step: based on the force peak values ​​and force differential values ​​of the multiple battery cells, compare and analyze the safety performance of the multiple groups of positive electrode materials; wherein the safety performance includes the external force resistance and thermal stability of the positive electrode material.

[0043] This test method performs a needle penetration test on battery cells assembled with multiple groups of positive electrode materials under the same test conditions. During the test, the force value and test time of the battery cells are recorded to obtain the data relationship between the force value and the test time, and then the peak force value and force differential value of the positive electrode material during the needle penetration process are obtained from the data relationship between the force value and the test time. The external force resistance and thermal stability of the multiple groups of positive electrode materials are evaluated based on the peak force value and the force differential value, respectively, so as to comprehensively evaluate the safety performance of the multiple groups of positive electrode materials.

[0044] S1. In the material packaging step, multiple groups of positive electrode materials to be evaluated are selected, and the multiple groups of positive electrode materials are respectively packaged into multiple battery cells. The assembled multiple battery cells should have the same capacity. For example, the capacity of the multiple battery cells after assembly is 1Ah or 2Ah. Among them, the type of battery cell that encapsulates the positive electrode material may not be limited. For example, the battery cell may be a square shell battery cell or a soft-pack battery cell. Preferably, in some embodiments, the battery cell assembled for testing is a soft-pack battery cell. The use of soft-pack battery cells to encapsulate the positive electrode material can more accurately reflect the kinetic properties of the positive electrode material itself in the puncture test.

[0045] In addition, it should be noted that the positive electrode material selected in the test method can be a common positive electrode material on the market, or a positive electrode material modified by doping and coating. For example, the positive electrode material in the test can be selected from ternary nickel cobalt manganese oxide LiNi 0.33 Co 0.33 Mn 0.33 O2 (NCM333) positive electrode material, LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) positive electrode material, LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) positive electrode material, LiNi 0.6 Co 0.1 Mn 0.3 O2 (NCM613) positive electrode material, LiNi 0.7 Co 0.1 Mn 0.2 O2 (NCM712) positive electrode material, LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811) positive electrode material, Y-doped nickel cobalt manganese oxide NCM811 positive electrode material, Al-coated nickel cobalt manganese oxide NCM811 positive electrode material and lithium iron phosphate LiFePO4 (LFP) positive electrode material.

[0046] In some embodiments, in the material packaging step, the process of assembling the positive electrode material into a soft-pack battery cell includes:

[0047] Preparation of positive electrode sheet: The positive electrode material, positive electrode conductive agent and positive electrode binder are dispersed in a solvent (such as N-methylpyrrolidone, referred to as NMP) to form a uniform positive electrode slurry: The positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, a positive electrode sheet is obtained;

[0048] Preparation of negative electrode sheet: Disperse the negative electrode material, negative electrode binder, thickener and negative electrode conductive agent in deionized water to form a uniform negative electrode slurry: Apply the negative electrode slurry on the negative electrode collector, and obtain the negative electrode sheet after drying, cold pressing and other processes. The ratio between the components in the negative electrode slurry can be set according to the conventional ratio and is not limited here. Among them, the negative electrode material is selected from one or more of artificial graphite, natural graphite, soft carbon, hard carbon, pure silicon, silicon oxide compounds, and silicon carbon compounds.

[0049] Preparation of diaphragm: The diaphragm is selected from conventional types in the art, for example, a PE porous membrane is selected as the diaphragm, the thickness of the diaphragm is 9 to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL; the porosity is 30% to 50%.

[0050] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0051] Cell assembly: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed between the positive and negative electrode sheets to play a role of isolation. Then, the aluminum plastic film is wrapped, and after drying, the above-prepared electrolyte is injected. After packaging, standing, and forming, the soft-pack cell is finally obtained.

[0052] In some embodiments, in the material packaging step, multiple cells are charged to the same set charge at the same charging rate so that the subsequent acupuncture experiment simulates the thermal effect of short-circuit discharge of the positive electrode material and the negative electrode material. Wherein, multiple cells have the same SOC (State of Charge) at the same set charge, for example, the set charge can be fully charged.

[0053] In this embodiment, the charging rate of the battery cell is 0.1C to 5C. Further, the charging rate of the battery cell is 0.1C to 0.5C. For example, the charging rate may be 0.1C, 0.2C, 0.333C or 0.5C.

[0054] S2. In the test steps, for each battery cell to be tested, the same fixture is used to clamp the test needle, and the battery cell is punctured at the same puncture rate. During the puncture process, the reaction force of the test needle received by the battery cell is collected, and the reaction force received by the test needle is used as the force value of the battery cell during the puncture process. Then, the corresponding relationship between the force value of the battery cell during the puncture process and the test time is recorded as the puncture test result of the battery cell.

[0055] In some embodiments, in the testing step, the aperture of the fixture is 10 to 20 mm, for example, the aperture of the fixture can be 10 mm, 12 mm, 15 mm, 17 mm or 20 mm; the test needle is a steel needle or a ceramic needle, and the diameter of the test needle is 5 to 10 mm, for example, the diameter of the test needle can be 5 mm, 8 mm or 10 mm; during the test, the puncture rate of the test needle is 50 to 100 mm / s, for example, the puncture rate can be 50 mm / s, 60 mm / s, 70 mm / s, 80 mm / s, 90 mm / s or 100 mm / s.

[0056] like Figure 4 As shown, in some embodiments, during the acupuncture process, the acupuncture site of the test needle on the battery cell is located at the center of the body of the battery cell.

[0057] like Figure 2 As shown, in S3, data processing step, the following data processing steps can be performed for the puncture test results of each battery cell:

[0058] S31, obtaining a force value-time curve of the battery cell during the acupuncture process based on the data relationship between the force value and the test time of the battery cell during the acupuncture process;

[0059] S32, based on the force value-time curve, selecting a maximum force value from the force value-time curve as the force peak value of the battery cell during the acupuncture process;

[0060] S33, performing differential processing on the force value-time curve to obtain a force value differential curve of the battery cell;

[0061] S34. Obtaining the force difference value of the battery cell from the force value difference curve.

[0062] In some embodiments, step S33 includes: taking the test time as the independent variable, calculating the slope value of each point on the force value-time curve to obtain the data relationship between the slope value and the test time on the force value-time curve; and then obtaining the force value differential curve corresponding to the force value-time curve of the battery cell according to the data relationship between the slope value and the test time.

[0063] In some embodiments, step S34 includes: intercepting the upper limit and lower limit of the force value on the force value differential curve; and then calculating the absolute value of the difference between the upper limit and the lower limit based on the upper limit and the lower limit of the force value to obtain the force differential value of the battery cell during the acupuncture process.

[0064] In addition, the inventors have verified that during the needle puncture test, the voltage of the battery cell will first decrease as the force value increases, and then decrease as the force value decreases. Among them, in the increase and decrease stages of the needle puncture force value, the change in the force value of the battery cell and the drop in the battery cell voltage have the same change trend. This same change trend can be specifically reflected in the mirror difference trend of the force value difference curve and the voltage difference curve with the test time as the independent variable.

[0065] During the test, the voltage drop of the battery cell indicates the discharge reaction process when the battery cell material is short-circuited by a needle, and the instantaneous voltage drop of the battery cell can also represent the reaction intensity of the battery cell in short-circuit thermal runaway. The change trend of the voltage differential curve is opposite to that of the voltage differential curve, which can accurately reflect the voltage change trend of the battery cell during the needle-puncture process. The maximum force differential value in the force differential curve represents the reaction intensity of the battery cell in short-circuit thermal runaway (that is, the maximum voltage drop rate), so as to evaluate the thermal stability of the positive electrode material in the battery cell.

[0066] For example, in some embodiments, the puncture test results of the battery cell also include the data relationship between the voltage and the test time of the battery cell during the puncture process, and the voltage differential curve of the battery cell during the puncture process is obtained based on the data relationship between the voltage and the test time in the puncture test results, and finally the accuracy of the force differential curve in evaluating the thermal stability performance of the positive electrode material is verified by comparing the voltage differential curve.

[0067] Taking the positive electrode material NCM811 as an example, a cell equipped with the positive electrode material NCM811 was subjected to a needle puncture test, and during the needle puncture test, the data relationship between the force value and voltage of the cell and the test time was recorded. Then, based on the above data relationship, the force value / voltage-time curve of the cell during the needle puncture process was obtained respectively, and the force value / voltage-time curve was differentially processed with the test time as the independent variable to obtain the force value / voltage differential curve.

[0068] Afterwards, by comparing the force value / voltage-time curve and the force value / voltage difference curve in this embodiment to determine the force value and voltage change trends, the consistency of the force difference value and the voltage difference value can be verified. Figure 5 As shown in the force value / voltage-time curve of this embodiment, the increasing trend of the cell force value in the increasing stage is the same as the voltage decreasing trend, and the decreasing trend of the cell force value in the decreasing stage is also the same as the voltage decreasing trend. Figure 6 As shown in the figure, the force value difference curve and voltage difference curve obtained by differential processing can be coupled with each other, and the force value difference curve and the voltage difference curve have mirror-opposite change trends. When the voltage difference is large, the instantaneous voltage drop of the battery cell is large, thermal runaway is more likely to occur, and the thermal safety performance of the positive electrode material is also poor. Therefore, in the test, the force difference value can be used to judge the value of the voltage difference value and accurately evaluate the thermal stability performance of the positive electrode material in the battery cell.

[0069] Therefore, based on the above verification, in S4, the performance evaluation step, the external force resistance and thermal stability of the corresponding positive electrode material can be evaluated respectively according to the peak force value and force differential value of the battery cell measured in the test.

[0070] Specifically, Figure 3 As shown, S4, the performance evaluation step includes:

[0071] S41. Compare the force peaks measured by multiple battery cells and analyze the superiority of the corresponding groups of positive electrode materials in terms of their resistance to external forces. If the force peak of the battery cell during the acupuncture process is larger, it means that the positive electrode material in the battery cell has better resistance to external forces; if the force peak of the battery cell during the acupuncture process is smaller, it means that the positive electrode material in the battery cell has worse resistance to external forces.

[0072] S42. Compare the force differential values ​​measured for multiple battery cells and analyze the excellence of the thermal stability of the corresponding multiple groups of positive electrode materials. The smaller the force differential value of the battery cell during the acupuncture process, the better the thermal stability of the positive electrode material in the battery cell; the larger the force differential value of the battery cell during the acupuncture process, the worse the thermal stability of the positive electrode material in the battery cell.

[0073] The technical scheme of the present invention is described in detail by the following examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0074] Example 1

[0075] S1. Material packaging step: select positive electrode materials NCM333, NCM523, NCM622, NCM613, NCM712, NCM811, modified NCM811 coated with Al element and LFP as the positive electrode materials to be tested, assemble the above positive electrode materials to be tested into soft-pack cells with a capacity of 1Ah, and charge multiple soft-pack cells to full charge at a constant voltage charging rate of 0.2C.

[0076] The steps of assembling the positive electrode material into a soft-pack battery cell are as follows:

[0077] Preparation of positive electrode sheet: dissolving positive electrode material, conductive agent acetylene black, and binder polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 95:3:2, mixing and homogenizing, coating on aluminum foil, drying, cold pressing, and cutting to obtain positive electrode sheet;

[0078] Preparation of negative electrode sheets: The negative electrode material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickener sodium carbon methyl cellulose are fully stirred and mixed in a deionized water solvent system in a mass ratio of 96:2:1:1, and then coated on a copper foil, dried, cold pressed, and cut to obtain a negative electrode sheet.

[0079] Preparation of the diaphragm: A polyethylene with a thickness of 9 μm was used as a base film, and a nano-aluminum oxide coating with a thickness of 3 μm was coated on the base film to obtain a diaphragm.

[0080] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0081] Assembling battery cells: stack the prepared positive electrode sheets, separators, and negative electrode sheets in sequence, and obtain bare battery cells after stacking to 11 layers. Put the bare battery cells into aluminum-plastic film, and then bake them at 80°C to remove water, inject the corresponding electrolyte and seal them. After that, a soft-pack battery cell with a capacity of 1Ah is obtained through processes such as standing, hot and cold pressing, formation, clamping, and capacity division.

[0082] S2. Test steps: Use the same test conditions to perform needle puncture tests on multiple soft-pack batteries. The test conditions are to use a fixture with a hole diameter of 20 mm to clamp a steel needle with a diameter of 8 mm, and make the steel needle puncture the center of the soft-pack battery at a puncture rate of 80 mm / s. During the puncture process, the data relationship between the force value and the test time of each soft-pack battery is recorded.

[0083] S3, data processing steps: based on the data relationship between the force value and the test time of the soft-pack battery cell during the acupuncture process, the force value-time curve of the soft-pack battery cell is obtained, and the maximum force value is screened from the force value-time curve as the force peak value; and the force value-time curve is further differentially processed to obtain a force value differential curve, and the upper limit value and the lower limit value of the force differential are intercepted from the force value differential curve, and the absolute value of the difference between the two values ​​is calculated to obtain the force differential value.

[0084] S4, performance evaluation steps: Compare the peak force values ​​of multiple soft-pack battery cells, and analyze the excellent external force resistance performance of the corresponding positive electrode material to be tested; compare the differential force values ​​of multiple soft-pack battery cells, and analyze the excellent thermal stability performance of the corresponding positive electrode material to be tested.

[0085] The needle penetration test results of multiple groups of positive electrode materials to be tested in Example 1 are shown in Table 1.

[0086] Table 1: Peak force and differential force of multiple groups of positive electrode materials tested during acupuncture in Example 1

[0087]

[0088]

[0089] As shown in Table 1 and Figure 7 As shown in the figure, in the test, the positive electrode material with a larger force peak has better resistance to external forces. For example, the LFP material with the best safety performance has the largest force peak in the test and the best resistance to external forces; the NCM333 material with the second-best safety performance has a larger force peak in the test and its resistance to external forces is similar to that of the LFP material; the NCM811 material with the worst safety performance has the smallest force peak in the test and the worst resistance to external forces.

[0090] As shown in Table 1 and Figure 8 As shown in the figure, in the test, the smaller the force differential value of the positive electrode material is, the better the thermal stability is. For example, the force differential value of NCM811 material in the test is the smallest, and the thermal stability is the best; the force differential values ​​of NCM333, NCM523, and LFP materials in the test are at the same level, and all have good thermal stability; the NCM712 and NCM811 materials with the second worst and worst safety performance have large force differential values ​​in the test and poor thermal stability.

[0091] As shown in Table 1, Figure 7 and Figure 8As shown in the figure, the external force resistance and thermal stability of the NCM811 material with the worst safety performance are greatly improved after being modified by Al element coating. This is specifically reflected in the significant increase in the peak force value and the significant decrease in the force differential value of the modified NCM811 material in the test. After comparing the test results, it can also be seen that the external force resistance and thermal stability of the modified NCM811 material both exceed those of the LFP material with the best safety performance.

[0092] In summary, in this needle puncture test method, by comparing the force peak and force differential values ​​of the positive electrode material assembled battery during the needle puncture process, the excellent performance of the positive electrode material in resisting external forces and thermal stability can be accurately evaluated. This test method is closer to the actual working environment of the positive electrode material during the test process, and can relatively accurately evaluate the safety performance of the positive electrode material in the soft-pack battery, and the test data and evaluation structure are more valuable for reference.

[0093] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for testing the safety performance of a positive electrode material, characterized in that: include: Material packaging step: assembling multiple groups of positive electrode materials into battery cells respectively; charging the multiple battery cells to a set power; Testing step: performing a needle puncture test on the battery cells respectively under the same conditions to obtain a needle puncture test result of each battery cell; wherein the needle puncture test result includes a data relationship between a force value and a test time of the battery cell during the needle puncture process; Data processing step: obtaining force peak values ​​and force differential values ​​of the multiple battery cells according to the acupuncture test results of the multiple battery cells; Performance evaluation step: based on the force peak values ​​and force differential values ​​of the multiple battery cells, comparing and analyzing the safety performance of the multiple groups of positive electrode materials.

2. The method for testing the safety performance of positive electrode materials according to claim 1, characterized in that: In the data processing step, the data processing of the puncture test result of each battery cell includes: Based on the data relationship between the force value and the test time of the battery cell during the acupuncture process, a force value-time curve of the battery cell during the acupuncture process is obtained; Based on the force value-time curve, obtaining the force peak value of the battery cell during the acupuncture process; Performing differential processing on the force value-time curve to obtain a force value differential curve of the battery cell; The force difference value of the battery cell is obtained from the force value difference curve.

3. The positive electrode material safety performance testing method according to claim 2, characterized in that: The step of performing differential processing on the force value-time curve to obtain the force value differential curve of the battery cell includes: Obtaining the data relationship between the slope value and the test time on the force value-time curve; According to the data relationship between the slope value and the test time, a force value difference curve of the battery cell is obtained.

4. The positive electrode material safety performance testing method according to claim 2, characterized in that: The obtaining the force difference value of the battery cell from the force difference curve comprises: intercepting the upper limit value and the lower limit value of the force value on the force value difference curve; The force differential value of the battery cell is obtained according to the upper limit value and the lower limit value of the force value.

5. The positive electrode material safety performance testing method according to claim 1, characterized in that: The performance evaluation steps include: Comparing the force peak values ​​of the multiple battery cells, and analyzing the external force resistance performance of the corresponding multiple groups of positive electrode materials; The force differential values ​​of the multiple battery cells are compared to analyze the thermal stability performance of the corresponding multiple groups of positive electrode materials.

6. The positive electrode material safety performance testing method according to claim 1, characterized in that: In the material packaging step, charging the plurality of battery cells to a set power level includes: The plurality of battery cells are charged to the same set power using the same charging rate; wherein the charging rate is 0.1C to 5C.

7. The positive electrode material safety performance testing method according to claim 1, characterized in that: During the puncture test, a fixture is used to clamp the test needle, and the plurality of battery cells are punctured at the same puncture rate.

8. The positive electrode material safety performance testing method according to claim 7, characterized in that: The aperture of the fixture is 10 to 20 mm, the test needle is a steel needle or a ceramic needle, the diameter of the test needle is 5 to 10 mm, and the puncture rate is 50 to 100 mm / s.

9. The positive electrode material safety performance testing method according to claim 7, characterized in that: The puncture point of the testing needle on the battery core is located at the center of the package of the battery core.

10. The positive electrode material safety performance testing method according to claim 1, characterized in that: The test results also include the data relationship between the voltage and the test time of the battery cell during the acupuncture process.

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