Method for detecting metal foreign matters in pole piece and evaluating quality of pole piece

Abstract

The invention belongs to the technical field of battery performance detection, and particularly discloses a method for detecting metal foreign matters in a pole piece and evaluating the quality of the pole piece, and the method for detecting the metal foreign matters in the pole piece comprises the following steps: (1) mixing a to-be-detected pole piece with a first solvent, and carrying out first ultrasonic treatment on the obtained first mixture, enabling the dressing on the to-be-detected pole piece to fall off to obtain a current collector and first turbid liquid containing the dressing; (2) carrying out adsorption treatment on the first turbid liquid by utilizing a permanent magnet, and collecting an adsorption product adsorbed on the permanent magnet to obtain metal foreign matters; and (3) detecting the metal foreign matters by using a cleanliness instrument to obtain metal foreign matter detection information. The method can detect foreign matters on the surface of the pole piece and in the dressing, the detection range is wider, and the quality of the pole piece can be evaluated more accurately.

Description

Technical Field

[0001] The present application belongs to the technical field of battery performance detection, and specifically relates to a method for detecting metal foreign matter in a pole piece and evaluating the pole piece quality. Background Art

[0002] In electric vehicles and energy storage systems, the secondary batteries used are composed of a positive electrode-diaphragm-negative electrode and an electrolyte free therein. During the charge and discharge process of the secondary battery, due to the change in the potential of the positive and negative electrodes, the remaining metal foreign matter in the positive and negative electrode sheets dissolves at the positive electrode and then precipitates at the negative electrode. The precipitated metal will not only affect the self-discharge performance of the battery, but in severe cases it will also pierce the diaphragm and short-circuit the positive and negative electrodes, thereby creating the risk of battery failure, heating, fire and even explosion. Methods for detecting metal foreign matter have also been described in the related art, but the current methods can only remove and evaluate foreign matter on the surface of the electrode sheet, and there is a risk of distorted measurement results during the detection process. Therefore, the method of detecting metal foreign matter in the electrode sheet still needs to be further improved. Summary of the invention

[0003] The present application aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the present application proposes a method for detecting metal foreign matter in a pole piece and evaluating the pole piece quality with a wider detection range or more accurate detection results.

[0004] The first aspect of the present application proposes a method for detecting metal foreign matter in a pole piece, comprising:

[0005] (1) mixing a test electrode and a first solvent, and subjecting the obtained first mixture to a first ultrasonic treatment so that the dressing on the test electrode falls off, thereby obtaining a current collector and a first suspension containing the dressing;

[0006] (2) using a permanent magnet to perform adsorption treatment on the first suspension, collecting adsorption products adsorbed on the permanent magnet, and obtaining metal foreign matter;

[0007] (3) Using a cleanliness meter to detect the metal foreign matter, and obtain metal foreign matter detection information.

[0008] The above detection method of the present application can detect foreign matter on the surface of the electrode and in the dressing, with a wider detection range and more accurate detection results.

[0009] In some embodiments, the dust level of the detection environment is ISO level 9 or above.

[0010] In some embodiments, the dew point of the detection environment is -10°C to -50°C.

[0011] In some embodiments, the temperature of the detection environment is 15°C to 25°C.

[0012] Within the above-mentioned detection environment range, it is beneficial to improve the accuracy of the detection results.

[0013] In some embodiments, before the first ultrasonic treatment, the method further includes: heating the first mixture, thereby facilitating the shedding of the dressing on the electrode to be tested.

[0014] In some embodiments, the temperature of the heating treatment is 25°C to 60°C.

[0015] In some embodiments, the heating treatment time is 0.5h to 2h.

[0016] In some embodiments, the first solvent includes at least one of an oily solvent and an aqueous solvent, the oily solvent includes at least one of N,N-dimethylpyrrolidone, acetone, dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran; the aqueous solvent includes at least one of water and alcohol. Thus, the solvent has a wide range of sources and a wide range of choices.

[0017] In some embodiments, the power of the first ultrasonic treatment is 4000W to 5000W, the frequency of the first ultrasonic treatment is 35KHz to 45KHz, the time of the first ultrasonic treatment is 1h to 2h, and the temperature of the first ultrasonic treatment is 25° C. to 60° C. This is conducive to efficiently removing the dressing and reducing test errors.

[0018] In some embodiments, step (1) includes: subjecting the first mixture to the first ultrasonic treatment to obtain a current collector and a second suspension; using the first solvent to wash the current collector after the first ultrasonic treatment at least once to obtain a cleaning solution; and mixing the cleaning solution with the second suspension to obtain the first suspension. Thus, the dressing collects more completely, which is conducive to improving the detection accuracy.

[0019] In some embodiments, in step (2), the adsorption treatment includes: coating the permanent magnet and placing it in the first suspension. Thus, the adsorption effect on the metal foreign matter is better, which is conducive to improving the detection accuracy.

[0020] In some embodiments, the material of the envelope includes one of polyethylene and polypropylene.

[0021] In some embodiments, the thickness of the envelope is 100 μm to 1000 μm.

[0022] In some embodiments, the magnetic field strength of the permanent magnet is 6000 GS to 14000 GS.

[0023] In some embodiments, the adsorption treatment is performed 1 to 3 times.

[0024] Under the above adsorption conditions, it is beneficial to improve the adsorption efficiency of permanent magnets on metal foreign matter.

[0025] In some embodiments, in step (2), after the adsorption treatment, the step further includes: removing the oxide layer on the surface of the adsorbed product to obtain the metal foreign matter, thereby improving the gloss of the metal foreign matter and facilitating subsequent cleanliness instrument detection.

[0026] In some embodiments, removing the oxide layer comprises: mixing the adsorbed product with an acidic solution, subjecting the obtained second mixture to a second ultrasonic treatment, and then washing, filtering and drying in sequence to obtain the metal foreign matter. This allows the adsorbed product to be in more complete contact with the acidic solution, and removing the oxide layer will not substantially affect the morphology of the metal foreign matter, thereby improving the accuracy of the test results.

[0027] In some embodiments, the acidic solution includes at least one of a hydrochloric acid solution, a nitric acid solution and a sulfuric acid solution. Thus, the material source is wide and the cost is low.

[0028] In some embodiments, the acid concentration in the acidic solution is 10% to 15%, which is helpful to improve the pickling efficiency.

[0029] In some embodiments, the power of the second ultrasonic treatment is 4000W to 5000W, the frequency of the second ultrasonic treatment is 35KHz to 45KHz, the ultrasonic time is 1min to 3min, and the temperature is room temperature, which is conducive to improving the ultrasonic efficiency.

[0030] In some embodiments, the filter membrane used for the suction filtration includes any one of a polyethylene (PE) filter membrane, a polytetrafluoroethylene (PTFE) filter membrane, and a polypropylene (PP) filter membrane. Thus, the material source is wide and the cost is low.

[0031] In some embodiments, the diameter of the filter membrane is 47 mm to 100 mm, and the pore size of the filter membrane is 1.2 μm to 10 μm. This is beneficial to improving the filtration efficiency and facilitating the subsequent direct use in cleanliness instrument testing.

[0032] In some embodiments, the drying temperature is 50° C. to 70° C., and the drying time is 10 min to 30 min. This is beneficial to improving the drying efficiency.

[0033] In some embodiments, the metal foreign matter detection information includes at least one of the mass of the metal foreign matter, the particle size of the metal foreign matter, and the number of particles of the metal foreign matter. Thus, the detection range of the detection method is wider.

[0034] The second aspect of the present application proposes a method for evaluating the quality of a pole piece, comprising:

[0035] Using the method described in the first aspect of the present application to detect the metal foreign matter in the pole piece, and obtain the particle size and particle quantity of the metal foreign matter;

[0036] The metal foreign matter index is calculated according to the following formula

[0037]

[0038] Wherein, x represents the particle size of the metal foreign matter, n a≤x＜b represents the number of particles of the metal foreign matter whose particle size satisfies x∈[a, b), n x≥b represents the number of particles of the metal foreign matter whose particle size satisfies x∈[b,∞), m represents the weight of the dressing on the electrode to be tested, a represents the lower limit particle size of the metal foreign matter, b represents the critical particle size of the metal foreign matter, and 0≤a<b, the particle size x is in μm, and the unit of m is kg.

[0039] In some embodiments, 1000 μm ≥ b ≥ 100 μm.

[0040] The present application adopts the above method to evaluate the quality of the electrode, which is beneficial to improve the accuracy of the evaluation results, and has lower costs, can achieve rapid detection, and has a higher degree of automation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the pole piece cut into strips in Example 1 of the present application.

[0042] Figure 2 This is a picture of the current collector in the fifth step of Example 1 of the present application.

[0043] Figure 3 This is a schematic diagram of using a PE bag to wrap a permanent magnet in Example 1 of the present application.

[0044] Figure 4 It is a schematic diagram of dispersing the collected metal foreign matter on the filter membrane in Example 1 of the present application.

[0045] Figure 5 This is a schematic diagram of using a cleanliness meter to detect metal foreign matter in Example 1 of the present application. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

[0047] The first aspect of the present application proposes a method for detecting metal foreign matter in a pole piece, comprising:

[0048] S1: mixing the electrode to be tested and a first solvent, and performing a first ultrasonic treatment on the obtained first mixture so that the dressing on the electrode to be tested falls off, thereby obtaining a current collector and a first suspension containing the dressing.

[0049] It should be noted that the pole piece can be pre-processed before testing. After coating or roller cutting, the pole piece is cut into a certain size with a ceramic knife and stored in a plastic bag that has been dusted and demagnetized. The plastic bag must not be opened during the transfer process to ensure that no metal foreign matter is introduced during the cutting and transfer process, and the test results are accurate. Among them, the pole piece can be cut into the size of the test container or the pole piece can be cut into filaments, strips, etc. The cutting tools and test containers are all non-metallic materials, and plastic, ceramic, etc. can be selected.

[0050] In some embodiments, before the electrode to be tested and the first solvent are mixed, the first solvent may be filtered through a filter. The filter is made of non-metallic material, such as a nylon filter, and the filter mesh number is 800-1000 mesh.

[0051] In some embodiments, the dust level of the detection environment is ISO level 9 or above. The dust level affects the test results. If there are many impurities in the environment, they may enter the collected metal foreign matter and affect the test results.

[0052] In some embodiments, the dew point of the detection environment is -10°C to -50°C, for example, -10°C, -20°C, -30°C, -40°C or -50°C, etc. It can be understood that for unsaturated air, if the temperature of the humid air is lowered while keeping the water vapor partial pressure in the humid air unchanged, the water vapor can be saturated from the overheated state. The humid air state corresponding to the state point is called the dew point of the humid air, and the temperature at the dew point is called the dew point temperature. Under certain conditions of the humid air temperature, the higher the dew point temperature, the higher the water vapor partial pressure in the humid air, the higher the water vapor content, and the more humid the humid air. Conversely, the drier the humid air, so the high or low dew point temperature of the humid air can indicate the humidity of the humid air.

[0053] In some embodiments, the temperature of the detection environment is 15°C to 25°C, for example, it can be 15°C, 18°C, 20°C, 22°C or 25°C.

[0054] It is understandable that the commonly used binders in the current pole pieces include polyvinylidene fluoride (PVDF). When the dressing in the pole piece to be tested contains PVDF, it is easy to absorb water and react to cause aggregation. If the water content in the test environment is higher, the PVDF is easy to agglomerate and difficult to disperse. By controlling the dew point and temperature of the test environment within the above range, the water content in the test environment is less, and it is easy for the dressing in the pole piece to be tested to be dispersed in the first solvent. Of course, it is also understandable that when there is no substance such as PVDF in the pole piece to be tested that is easy to absorb water and react to cause aggregation, there is no need to perform special control on the test environment.

[0055] In some embodiments, before the first ultrasonic treatment, the method further includes: heating the first mixture, thereby facilitating the shedding of the dressing on the electrode to be tested.

[0056] In some embodiments, the temperature of the heating treatment is 25°C to 60°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc.; the time of the heating treatment is 0.5h to 2h, for example, 0.5h, 1h, 1.5h or 2h, etc. Thus, the binder in the electrode can be dissolved, which is conducive to the rapid shedding of the dressing on the electrode to be tested.

[0057] In some embodiments, the first solvent includes at least one of an oily solvent and an aqueous solvent, the oily solvent includes at least one of N,N-dimethylpyrrolidone, acetone, dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran; the aqueous solvent includes at least one of water and alcohol. It is understood that the pole piece can use an oily solvent or an aqueous solvent, which can be flexibly selected according to specific circumstances.

[0058] As an example, whether the first solvent is an oily solvent or a water-washing solvent can be selected according to the type of material in the dressing in the electrode to be tested or the solvent used when preparing the dressing layer. For example, if the material in the dressing is easier to disperse in an oily solvent, or an oily solvent is used to prepare the slurry when preparing the dressing layer, the first solvent can be an oily solvent; and if the material in the dressing is easier to disperse in an aqueous solvent, or an aqueous solvent is used to prepare the slurry when preparing the dressing layer, the first solvent can be an aqueous solvent. In this way, the dressing can be better dispersed, which is conducive to improving the detection accuracy.

[0059] In some embodiments, the ultrasonic power of the first ultrasonic treatment is 4000W~5000W (specifically 4100W, 4200W, 4300W, 4400W, 4500W, 4600W, 4700W, 4800W, 4900W, etc.), the frequency of the first ultrasonic treatment is 35KHz~45KHz (specifically 36KHz, 37KHz, 38KHz, 39KHz, 40KHz, 41KHz, 42KHz, 43KHz, 44KHz, etc.); the ultrasonic time is 1h~2h (such as 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h, etc.), and the ultrasonic temperature is 25℃~60℃ (such as 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, etc.). The present application adopts ultrasonic vibration for peeling, which is simple and quick, does not require large instruments such as fume hoods, and ultrasonic vibration can be used to test larger weights, reducing test errors.

[0060] In some embodiments, step S1 includes: performing the first ultrasonic treatment on the first mixture to obtain a current collector and a second suspension; using the first solvent to wash the current collector after the first ultrasonic treatment at least once to obtain a cleaning solution; and mixing the cleaning solution with the second suspension to obtain the first suspension. In this way, the loss of dressing can be reduced and the detection accuracy can be improved.

[0061] S2: using a permanent magnet to perform adsorption treatment on the first suspension, collecting adsorption products adsorbed on the permanent magnet, and obtaining metal foreign matter.

[0062] In this step, a permanent magnet may be placed in the first suspension and stirred sufficiently, thereby fully absorbing the metallic foreign matter in the first suspension and improving the detection accuracy.

[0063] In some embodiments, the permanent magnet coating is placed in the first suspension, and the adsorbed product on the permanent magnet is collected using the first solvent. Specifically, the coating can be removed from the permanent magnet, and then the coating can be cleaned using the first solvent to collect the adsorbed product. This makes it easier to collect the adsorbed product, reduces the loss of metal foreign matter, and improves the detection accuracy.

[0064] In some embodiments, the material of the envelope includes one of polyethylene and polypropylene.

[0065] In some embodiments, the thickness of the envelope is 100 μm to 1000 μm, for example, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm.

[0066] In some embodiments, the magnetic field strength of the permanent magnet is 6000GS to 14000GS, for example, it can be 6000GS, 7000GS, 8000GS, 9000GS, 10000GS, 11000GS, 12000GS, 13000GS, 14000GS, etc.

[0067] In some embodiments, the adsorption treatment is performed 1 to 3 times, for example, 1 time, 2 times, or 3 times.

[0068] Within the above adsorption conditions, it is beneficial to improve the adsorption efficiency of permanent magnets on metal foreign matter.

[0069] It can be understood that the principle of cleanliness meter detection is based on the reflection of light on the surface of metal foreign matter particles. The presence of an oxide layer on the surface of metal foreign matter will make the metallic luster of the surface weaker, which is not conducive to the reflection of light, and thus not conducive to the detection of cleanliness meter, and may affect the accuracy of the test results. In order to further improve the detection accuracy, in some embodiments, after the adsorption treatment, it also includes: removing the oxide layer on the surface of the adsorbed product to obtain the metal foreign matter. In this way, the surface gloss of the metal foreign matter can be improved, the reflection of light by the metal foreign matter can be increased, and the detection accuracy of the cleanliness meter can be improved.

[0070] Specifically, the oxide layer on the surface of the adsorbed product can be removed by pickling. In some embodiments, removing the oxide layer includes: mixing the adsorbed product with an acidic solution, subjecting the obtained second mixture to a second ultrasonic treatment, and then washing, filtering and drying in sequence to obtain the metal foreign matter. Thus, the oxide on the surface of the adsorbed product can be simply and quickly removed, and the ultrasonic treatment can make the surface of the adsorbed product fully mixed with the acidic solution, while removing the surface oxide layer, the size and morphology of the metal foreign matter are basically not destroyed, thereby improving the accuracy of detection. .

[0071] In some embodiments, the acidic solution includes at least one of a hydrochloric acid solution, a nitric acid solution and a sulfuric acid solution. Thus, the material source is wide and the cost is low.

[0072] In some embodiments, the acid concentration in the acidic solution is 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, etc. Therefore, within the above concentration range, the surface oxide layer can be removed efficiently without substantially destroying the size and morphology of the metal foreign matter.

[0073] In some embodiments, the power of the second ultrasonic treatment is 4000W to 5000W (specifically, 4100W, 4200W, 4300W, 4400W, 4500W, 4600W, 4700W, 4800W, 4900W, etc.), the frequency of the second ultrasonic treatment is 35KHz to 45KHz (specifically, 36KHz, 37KHz, 38KHz, 39KHz, 40KHz, 41KHz, 42KHz, 43KHz, 44KHz, etc.); the ultrasonic time of the second ultrasonic treatment is 1min to 3min (such as 1min, 2min or 3min, etc.), and the temperature of the second ultrasonic treatment is room temperature. Thus, it is beneficial to improve the ultrasonic efficiency.

[0074] In some embodiments, the filter membrane used for the suction filtration includes any one of a PE filter membrane, a PTFE filter membrane, and a PP filter membrane. Thus, the material source is wide and the cost is low.

[0075] In some embodiments, the diameter of the filter membrane is 47 mm to 100 mm (such as 47 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm, etc.), and the pore size of the filter membrane is 1.2 μm to 10 μm (such as 1.2 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.). This is conducive to improving the filtration efficiency and can be directly used for cleanliness detection.

[0076] In some embodiments, the drying temperature is 50°C to 70°C (such as 50°C, 55°C, 60°C, 65°C or 70°C), and the drying time is 10min to 30min (such as 10min, 15min, 20min, 25min or 30min). This is beneficial to improving the drying efficiency.

[0077] S3: Using a cleanliness meter to detect the metal foreign matter to obtain metal foreign matter detection information.

[0078] Among them, the detection principle of the cleanliness meter is based on the reflection of light on the surface of metal foreign matter particles. It can be completed fully automatically, recording the quantity, size, etc., and automatically outputting a report.

[0079] In some embodiments, the metal foreign matter detection information includes at least one of the mass of the metal foreign matter, the particle size of the metal foreign matter, and the number of particles of the metal foreign matter. Thus, the detection range of the detection method is wider.

[0080] The above detection method of the present application can detect foreign matter on the surface of the electrode and in the dressing, with a wider detection range and more accurate detection results.

[0081] The second aspect of the present application proposes a method for evaluating the quality of a pole piece, comprising:

[0082] The method described in the first aspect of the present application is used to detect metal foreign matter in the pole piece to obtain the particle size and particle quantity of the metal foreign matter. Specifically, the metal foreign matter can be divided into n intervals according to different particle size ranges, and the particle quantity of the metal foreign matter in each interval is calculated.

[0083] Then calculate the metal foreign matter index according to the following formula

[0084]

[0085] Wherein, x represents the particle size of the metal foreign matter, n a≤x＜b represents the number of particles of the metal foreign matter whose particle size satisfies x∈[a, b), n x≥b represents the number of particles of the metal foreign matter whose particle size satisfies x∈[b,∞), m represents the weight of the dressing on the electrode to be tested, a represents the lower limit particle size of the metal foreign matter, b represents the critical particle size of the metal foreign matter, and 0≤a<b, the particle size x is in μm, and the unit of m is kg.

[0086] It is understandable that the metal foreign matter index Indicates the number of metal foreign matter particles per unit weight in the pole piece. The larger the value, the worse the quality of the pole piece. It can be understood that the larger the volume of the metal foreign matter particles, the greater the impact on the performance of the pole piece. Therefore, when calculating the metal foreign matter index, When the particle size is smaller than the critical particle size, the metal foreign particles with a weight of 0.5 are assigned, that is, when the particle size is smaller than the critical particle size, two metal foreign particles are counted as one, and the metal foreign particles with a particle size larger than the critical particle size are assigned a weight of 1, that is, when the particle size is smaller than the critical particle size, one metal foreign particle is counted as one.

[0087] Specifically, the critical particle size can be selected according to actual production conditions, process requirements and product quality requirements, without special restrictions. In some embodiments of the present application, 1000 μm ≥ b ≥ 100 μm, for example, b can be 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm or 1000 μm, etc.

[0088] The lower limit particle size can be adjusted according to the sensitivity of the test. Of course, if the lower limit particle size is 0, the detection accuracy will be higher. It can be flexibly selected and adjusted according to the actual situation.

[0089] In some specific examples, a may be 25, b may be 100, and the formula for calculating the metal foreign matter index is:

[0090]

[0091] Among them, n 25≤x＜100 represents the number of particles of the metal foreign matter whose particle size satisfies x∈[25,100), n x≥100 represents the number of particles of the metal foreign matter whose particle size satisfies x∈[100,∞).

[0092] The present application adopts the above method to evaluate the quality of the electrode, which is beneficial to improve the accuracy of the evaluation results, and has lower costs, can achieve rapid detection, and has a higher degree of automation.

[0093] As an example, a method for detecting metal foreign matter in a pole piece and evaluating the pole piece quality includes the following steps:

[0094] (1) Electrode pretreatment: The electrode is immersed in a solvent at high temperature, and the electrode dressing is vibrated by an ultrasonic device to remove the electrode dressing to obtain suspension 1, and the current collector after the dressing is removed is rinsed with the same solvent to obtain suspension 2, and all the suspensions are mixed to obtain suspension 3;

[0095] (2) Collection of metallic foreign matter: After the permanent magnet is coated, it is placed in the suspension 3, so that the permanent magnet is fully stirred in the suspension 3 to adsorb the metallic foreign matter in the suspension 3, the coating is separated, and the metallic foreign matter is collected. The above steps are repeated 3 times to obtain 3 portions of metallic foreign matter in total;

[0096] (3) Treatment of metal foreign matter: The three portions of metal foreign matter are combined and pickled to obtain treated metal foreign matter;

[0097] (4) Metal foreign matter assessment: The metal foreign matter after pickling is transferred to the filter membrane, and the size and quantity of the metal foreign matter on the filter membrane are measured by the cleanliness meter. Different algorithms are used to calculate the proportion of foreign matter of different sizes, which can accurately evaluate the cleanliness quality of the electrode per unit weight.

[0098] The embodiments of the present application are described in detail below.

[0099] Example 1

[0100] This example tests the positive electrode, which is made of oil-based solvents. First, confirm whether the dust content in the electrode collection location and the test room meets ISO9 level, and whether the environmental dew point is between -10℃ and -50℃. Prepare plastic bags that have been dusted and demagnetized in advance, and confirm that there are no equipment abnormalities or maintenance in the production workshop within one day;

[0101] In the first step, a ceramic knife is used to cut the coated or roll-cut electrode into about 0.7 kg, which is then manually folded and placed in a plastic bag and transferred to the inspection room.

[0102] The second step is, Figure 1As shown, the electrode is cut into strips using ceramic scissors and placed in a test container;

[0103] The third step is to pour the NMP solvent filtered through an 800-mesh nylon mesh into the test container, not covering the electrode, and heat the test container to 60°C and soak for 2 hours to dissolve the PVDF in the electrode in the NMP.

[0104] The fourth step is to place the test container in an ultrasonic instrument, and use a 4500W power, 40KHz ultrasonic instrument at a temperature of 60°C for 2 hours to make the dressing on the current collector fall off to obtain a suspension;

[0105] Step 5: Figure 2 As shown, the current collector is rinsed with NMP solvent so that the surface of the current collector has no material residue and has a metallic luster when observed with the naked eye, and the rinse liquid obtained by rinsing is mixed with the suspension obtained in the fourth step to obtain a mixed suspension;

[0106] Step 6: Figure 3 As shown, a cylindrical permanent magnet with a magnetic field strength of 12000GS is wrapped with a PE bag, and the permanent magnet is fully stirred in the mixed suspension obtained in the fifth step to adsorb the metal foreign matter in the mixed suspension. After each adsorption, the metal foreign matter adsorbed on the PE bag is dispersed in NMP again, and a new PE bag is used to wrap the permanent magnet for adsorption again. This action is repeated 3 times, and the adsorption products collected three times are combined.

[0107] In the seventh step, the adsorbed product obtained in the sixth step is placed in a hydrochloric acid solution with an acid concentration of 10%, and the hydrochloric acid solution is ultrasonicated for 5 minutes at a power of 4500W and a frequency of 40KHz at room temperature; and ultrapure water is used for rinsing. After the rinsing, the metal foreign matter is dispersed in ultrapure water, and the collected metal foreign matter is dispersed on a PP filter membrane with a diameter of 47mm and a pore size of 5μm using a suction filtration device; and the filter membrane is then dried in an oven at 80°C for 10 minutes. Figure 4 As shown;

[0108] In the eighth step, place the filter membrane in the seventh step on the cleanliness meter, adjust the light source and focus of the equipment to make the metal foreign matter clearly visible, and the equipment automatically outputs the morphology and particle size of the metal foreign matter, as well as the number of particles in different particle size ranges. Check the test results, manually cut the agglomerated particles that are not dispersed well, and recalibrate the metal particles with misaligned particle edge recognition. The test results are as follows: Figure 5 shown.

[0109] Example 2

[0110] This example tests the negative electrode, which is made of water-based solvents. First, confirm whether the dust content in the electrode collection location and the test room meets ISO9 level, and whether the environmental dew point is between -10℃ and -50℃. Prepare plastic bags that have been dusted and demagnetized in advance, and confirm that there are no equipment abnormalities or maintenance in the production workshop within one day;

[0111] In the first step, a ceramic knife is used to cut the coated or roll-cut electrode into pieces of about 0.2 kg, which are then manually folded and placed in a plastic bag and transferred to the inspection room.

[0112] The second step is to cut the electrode into strips using ceramic scissors and place them in the test container;

[0113] The third step is to pour the ultrapure water solvent into the test container, not covering the electrode, and soak it at 25°C for 30 minutes to dissolve the SBR in the electrode in the ultrapure water;

[0114] The fourth step is to place the test container in an ultrasonic instrument and use a 4500W power, 40KHz ultrasonic instrument at 25°C for 1 hour to make the dressing on the current collector fall off and obtain a suspension;

[0115] The fifth step is to rinse the current collector with the ultrapure water obtained in the third step, so that the current collector surface has no material residue and has a metallic luster when observed with the naked eye, and the rinse liquid obtained by rinsing is mixed with the suspension obtained in the fourth step to obtain a mixed suspension;

[0116] Step 6: Use a PE bag to wrap a cylindrical permanent magnet with a magnetic field strength of 12000GS, and fully stir the permanent magnet in the suspension obtained in the fifth step to adsorb the metal foreign matter in the suspension. After each adsorption, the metal foreign matter adsorbed on the PE bag is dispersed again in ultrapure water, and a new PE bag is used to wrap the permanent magnet for adsorption again. Repeat this action for a total of 3 times, and combine the adsorption products collected three times;

[0117] Step 7: Place the metal foreign matter obtained in step 6 in a hydrochloric acid solution with an acid concentration of 10%, and ultrasonicate the hydrochloric acid solution at 4500W power, 40KHz, and room temperature for 5 minutes; and rinse with ultrapure water. After rinsing, disperse the metal foreign matter in ultrapure water, and use a suction filtration device to disperse the collected metal foreign matter on a PP filter membrane with a diameter of 47mm and a pore size of 5μm; and then dry the filter membrane in an oven at 80°C for 10 minutes;

[0118] In the eighth step, place the filter membrane in the seventh step on the cleanliness meter, adjust the light source and focus of the equipment to make the metal foreign matter clearly visible, and the equipment automatically outputs the morphology and particle size of the metal foreign matter, as well as the number of particles in different particle size ranges. Check the test results, manually cut the agglomerated particles that are not dispersed well, and recalibrate the metal particles with misaligned particle edge identification.

[0119] The evaluation method for the pole piece quality in Examples 1 and 2 is as follows:

[0120] 1. The specific steps of the method for evaluating the quality of the pole piece in Example 1 are as follows:

[0121] The first step is to obtain the particle size and quantity of the metal foreign matter in the electrode piece in Example 1. The detection data is shown in Table 1 below.

[0122] In the second step, the metal foreign bodies in the first step are sorted in order from small to large, and the number is counted according to different particle size intervals. In this experiment, all particles are divided into 6 intervals, as shown in Table 1. The metal foreign body index of the pole piece is calculated according to the formula It is 72.86.

[0123] Table 1 Metal foreign body detection data of pole piece

[0124] Particle size (x) Number of particles (n) 10μm≤x<25μm 111 25μm≤x<50μm 37 50μm≤x<100μm 33 100μm≤x<200μm 11 200μm≤x<400μm 3 400μm≤x 2

[0125] 2. The specific steps of the method for evaluating the quality of the pole piece of Example 2 are as follows:

[0126] The first step is to obtain the particle size and quantity of metal foreign matter in the electrode in Experiment 2. The test data is shown in Table 2 below.

[0127] In the second step, the metal foreign bodies in the first step are sorted in order from small to large, and the number is counted according to different particle size intervals. In this experiment, all particles are divided into 10 intervals, as shown in Table 2. The metal foreign body index of the pole piece is calculated according to the formula It is 507.5.

[0128] Table 2 Metal foreign body detection data of pole piece

[0129] Particle size (x) Number of particles (n) 5μm≤x<15μm 137 15μm≤x<25μm 91 25μm≤x<50μm 88 50μm≤x<100μm 53 100μm≤x<150μm 20 150μm≤x<200μm 6 200μm≤x<400μm 3 400μm≤x<600μm 2 600μm≤x<1000μm 0 1000μm≤x 0

[0130] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present application, "plurality" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0131] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0132] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for detecting metal foreign matter in a pole piece, characterized in that: include: (1) mixing a test electrode and a first solvent, and subjecting the obtained first mixture to a first ultrasonic treatment so that the dressing on the test electrode falls off, thereby obtaining a current collector and a first suspension containing the dressing; (2) using a permanent magnet to perform adsorption treatment on the first suspension, collecting adsorption products adsorbed on the permanent magnet, and obtaining metal foreign matter; (3) Using a cleanliness meter to detect the metal foreign matter, and obtain metal foreign matter detection information.

2. The method according to claim 1, characterized in that The detection environment meets at least one of the following conditions: The dust level of the testing environment is ISO9 or above; The dew point of the detection environment is -10°C to -50°C; The temperature of the detection environment is 15°C to 25°C.

3. The method according to claim 1 or 2, characterized in that: Before the first ultrasonic treatment, the method further includes: heating the first mixture.

4. The method according to claim 3, characterized in that The heating treatment satisfies at least one of the following conditions: The temperature of the heating treatment is 25°C to 60°C; The heating treatment time is 0.5h to 2h.

5. The method according to any one of claims 1 to 4, characterized in that: The first solvent includes at least one of an oily solvent and an aqueous solvent, the oily solvent includes at least one of N,N-dimethylpyrrolidone, acetone, dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran; the aqueous solvent includes at least one of water and alcohol.

6. The method according to any one of claims 1 to 5, characterized in that: The first ultrasonic treatment satisfies at least one of the following conditions: The power of the first ultrasonic treatment is 4000W to 5000W; The frequency of the first ultrasonic treatment is 35KHz to 45KHz; The first ultrasonic treatment time is 1h to 2h; The temperature of the first ultrasonic treatment is 25°C to 60°C.

7. The method according to any one of claims 1 to 6, characterized in that: Step (1) comprises: performing the first ultrasonic treatment on the first mixture to obtain the current collector and a second suspension; Using the first solvent to clean the current collector after the first ultrasonic treatment at least once to obtain a cleaning solution; The cleaning liquid is mixed with the second suspension to obtain the first suspension.

8. The method according to any one of claims 1 to 7, characterized in that: In step (2), the adsorption treatment includes: coating the permanent magnet and placing it in the first suspension.

9. The method according to claim 8, characterized in that The adsorption treatment satisfies at least one of the following conditions: The material of the coating includes one of polyethylene and polypropylene; The thickness of the envelope is 100 μm to 1000 μm; The magnetic field strength of the permanent magnet is 6000GS to 14000GS; The number of times of the adsorption treatment is 1 to 3 times.

10. The method according to any one of claims 1 to 9, characterized in that: In step (2), after the adsorption treatment, the method further includes: removing the oxide layer on the surface of the adsorption product to obtain the metal foreign matter.

11. The method according to claim 10, characterized in that Removing the oxide layer includes: mixing the adsorption product with an acidic solution, subjecting the obtained second mixture to a second ultrasonic treatment, and then sequentially washing, filtering and drying to obtain the metal foreign matter.

12. The method according to claim 11, characterized in that Satisfy at least one of the following conditions: The acidic solution includes at least one of a hydrochloric acid solution, a nitric acid solution and a sulfuric acid solution; The mass concentration of acid in the acidic solution is 10% to 15%; The power of the second ultrasonic treatment is 4000W to 5000W; The frequency of the second ultrasonic treatment is 35KHz to 45KHz; The second ultrasonic treatment time is 1 min to 3 min; The temperature of the second ultrasonic treatment is room temperature; The filter membrane used for the filtration includes any one of a polyethylene filter membrane, a polytetrafluoroethylene filter membrane, and a polypropylene filter membrane; the diameter of the filter membrane is 47 mm to 100 mm; The pore size of the filter membrane is 1.2 μm to 10 μm; The drying temperature is 50°C to 70°C; The drying time is 10 min to 30 min.

13. The method according to any one of claims 1 to 12, characterized in that: The metal foreign matter detection information includes at least one of the mass of the metal foreign matter, the particle size of the metal foreign matter, and the number of particles of the metal foreign matter.

14. A method for evaluating the quality of a pole piece, characterized in that: include: Using the method described in any one of claims 1 to 13 to detect metal foreign matter in the pole piece, and obtain the particle size and particle quantity of the metal foreign matter; The metal foreign matter index is calculated according to the following formula Wherein, x represents the particle size of the metal foreign matter, n a≤x＜b represents the number of particles of the metal foreign matter whose particle size satisfies x∈[a, b), n x≥b represents the number of particles of the metal foreign matter whose particle size satisfies x∈[b,∞), m represents the weight of the dressing on the electrode to be tested, a represents the lower limit particle size of the metal foreign matter, b represents the critical particle size of the metal foreign matter, and 0≤a<b, the particle size x is in μm, and the unit of m is kg.

15. The method according to claim 14, characterized in that 1000μm≥b≥100μm.

Images