Method for detecting metal foreign matters in lithium ion slurry

Abstract

The invention belongs to the technical field of lithium batteries, and discloses a method for detecting metal foreign matters in slurry, which comprises the following specific steps: diluting positive or negative slurry by using a corresponding solvent, selecting a filter membrane with a proper pore size for first suction filtration, cleaning the filter membrane by using the solvent after the first suction filtration is finished, then performing second suction filtration on the cleaning solution, and leaving the filter membrane to be detected after the second suction filtration is finished; flatly laying a clean color developing filter membrane on a white background plate, dropwise adding an acid solution and an oxidizing solution in sequence, laying the filter membrane to be detected on the surface of the color developing filter membrane and infiltrating, dropwise adding a color developing agent after about 1 minute, indicating that the metal foreign matters exist if colored points appear on the surface of the filter membrane, and indicating that the number of the points is in positive correlation with the content of the metal foreign matters; and whether the slurry is qualified can be preliminarily judged according to the quantity. The method disclosed by the invention is simple to operate, less in time consumption and low in cost, can be used for detecting the slurry of the production line every shift, can quickly find abnormal samples and timely treat the abnormal samples, and improves the production efficiency and the production stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion slurry detection, and in particular to a method for detecting metallic foreign matter in lithium ion slurry. Background Art

[0002] Lithium-ion batteries have been widely used in energy storage, mobile devices, electric vehicles, aerospace and other fields due to their high energy density, long cycle life, high coulomb efficiency and wide operating temperature range. In the manufacturing process of lithium-ion batteries, due to the wear of equipment and pipelines, metal impurities may be mixed into the electrode materials, forming micro short circuits and causing battery self-discharge. Therefore, most production lines use inductively coupled plasma testing (ICP) to sample the slurry at fixed times to quantitatively analyze whether the magnetic impurity content exceeds the standard. This method is not only costly, but also time-consuming, with complex testing steps, which increases equipment costs and labor costs.

[0003] The Chinese patent application document with publication number CN110567999A discloses a SEM-EDS combined test method for metal foreign matter in lithium battery materials, including the following steps: adding high-purity water and lithium ion positive electrode materials to a test bottle, placing a magnet with a magnetic field strength of 5000GS to 6000GS in the test bottle, and mixing; pouring out the slurry, taking out the magnet, washing the material adhered to the magnet with high-purity water, ultrasonically washing it with an ultrasonic instrument, removing the magnet, washing and drying it; adhering the magnetic foreign matter on the magnet to a conductive tape; identifying the morphology and particle size of the magnetic foreign matter particles by SEM, determining the chemical composition and type of the foreign matter particles by energy spectrum analysis, and finally performing statistics on the magnetic foreign matter content according to the determined type, number and particle size of the metal foreign matter particles. However, the patent does not disclose the detection method of metal foreign matter in lithium ion slurry of the present invention. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to provide a simple-to-operate, low-cost method for detecting metallic foreign matter in slurry, which can quickly detect each batch of slurry and give a judgment result.

[0005] The present invention solves the above technical problems through the following technical means:

[0006] The present invention provides a method for detecting metallic foreign matter in lithium ion slurry, comprising the following steps:

[0007] S1: Take the slurry to be tested, add solvent to dilute and shake well;

[0008] S2: Filter the shaken slurry for the first time, discard the filtrate, and keep the filter membrane;

[0009] S3: placing the filtered membrane into a solvent for ultrasonic cleaning;

[0010] S4: Filter the cleaning liquid for the second time, discard the filtrate, and retain the filter membrane;

[0011] S5: Place a clean filter membrane on a watch glass, drip an acidic solution and an oxidizing solution onto the surface, spread the filter membrane obtained in step S5 onto the surface of the clean filter membrane, and let it stand for 1 minute;

[0012] S6: Add a color developer solution to the surfaces of the two overlapping filter membranes obtained in step S5, and wait for color to develop. If color is developed, it is determined that the slurry contains metallic foreign matter; if no color is developed, it is determined that the slurry does not contain metallic foreign matter.

[0013] Preferably, in step S1, the slurry to be detected is selected from one of positive electrode slurry or negative electrode slurry.

[0014] Preferably, in step S1, the solvent is one of deionized water and N,N-dimethylformamide (NMP).

[0015] Preferably, in step S1, the solid-liquid ratio of the slurry to be detected to the solvent is 1 g: 1.5-3 mL.

[0016] Preferably, in step S1, the material-liquid ratio of the slurry to be detected to the solvent is 1 g:2 mL.

[0017] Preferably, in step S2, the filtration is specifically as follows: select a filter membrane of suitable specifications, wash it with dilute hydrochloric acid and solvent respectively, put it into a Buchner funnel, pour in the shaken slurry, and then use the corresponding solvent to repeatedly rinse the container and the surface of the filter membrane to ensure that the main material is filtered cleanly.

[0018] Preferably, in step S3, ultrasonic cleaning is performed for 3 to 5 minutes.

[0019] Preferably, in step S5, the clean filter membrane is a 0.22 μm filter membrane.

[0020] Preferably, in step S5, the acidic solution is selected from dilute hydrochloric acid and dilute nitric acid.

[0021] Preferably, in step S5, the oxidizing solution is a hydrogen peroxide solution.

[0022] Preferably, in step S6, the developer is selected from potassium thiocyanate, dicarbohydrazide, and dimethylglyoxime.

[0023] The beneficial effects of the present invention are:

[0024] The method of the invention is simple to operate, takes less time, and is low in cost. The slurry of the production line can be tested every shift, and abnormalities can be quickly discovered and handled in a timely manner, thereby improving production efficiency and production stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1Figure 1 is a diagram of the suction filtration device used in the present invention;

[0026] Figure 2 This is a color development experiment operation diagram of the present invention;

[0027] Reference numerals: vacuum filtration pump 1, washing bottle 2, Buchner funnel 3, glass watch glass 4, filter membrane for color development plate 5, filter membrane for color development detection 6. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0030] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0031] Embodiment 1:

[0032] The present invention provides a method for detecting metallic foreign matter in lithium ion slurry.

[0033] S1: Pour 100g of nickel-cobalt-manganese cathode slurry into a homogenization bottle, add 200mL of N,N-dimethylformamide (NMP), and shake manually for 3-5min until it is completely diluted and has no precipitation;

[0034] S2: Take a 30μm filter membrane, wet it with dilute hydrochloric acid first, then wet it with NMP, put it into a Buchner funnel with a diameter of 60mm, pour the diluted slurry into it for suction filtration, and then rinse the filter membrane surface with NMP several times;

[0035] S3: Place the above filter membrane in a beaker containing NMP and clean it by ultrasonic for 5 minutes;

[0036] S4: Take another 30 μm filter membrane, wet it with dilute hydrochloric acid and NMP, and then put it into the Buchner funnel for a second filtration. After filtration, rinse the filter membrane surface several times with NMP.

[0037] S5: Take a 0.22 μm filter membrane, wet it with dilute hydrochloric acid and NMP, then add dilute hydrochloric acid to cover the filter membrane, then add hydrogen peroxide to cover the filter membrane, spread the above filtered filter membrane on the surface of the filter membrane, and let it stand for 1 minute;

[0038] S6: Use potassium thiocyanate (KSCN) as the color developer and add it dropwise to the surface of the filter membrane. After waiting for 3 to 5 minutes, a red dot will appear on the surface.

[0039] Embodiment 2:

[0040] The present invention provides a method for detecting metallic foreign matter in lithium ion slurry.

[0041] S1: Take 100g of negative electrode slurry from the main screw outlet and the coating machine head respectively, add 150mL of deionized water to each, and shake manually for 3-5min until it is completely diluted without precipitation;

[0042] S2: Take a 30μm filter membrane, wet it with dilute hydrochloric acid and deionized water, put it into a Buchner funnel and start to filter. After the filter is finished, rinse the surface with deionized water several times;

[0043] S3: Place the above filter membrane in a beaker filled with deionized water and clean it by ultrasonic cleaning for 5 minutes;

[0044] S4: Take another 30 μm filter membrane, wet it with dilute hydrochloric acid and deionized water, put it into the Buchner funnel for a second filtration, and rinse the filter membrane surface with deionized water several times after the filtration is completed;

[0045] S5: Take a 0.22 μm filter membrane, wet it with dilute hydrochloric acid and deionized water, then add dilute hydrochloric acid to cover the filter membrane, then add hydrogen peroxide to cover the filter membrane, spread the filtered filter membrane on the surface of the filter membrane, and let it stand for 1 minute;

[0046] S6: Select KSCN as the color developer and add it dropwise to the surface of the above filter membrane. Wait for 3 to 5 minutes. Four red dots will appear on the filter membrane at the outlet of the main screw and zero red dots will appear on the filter membrane at the coating machine head.

[0047] Embodiment 3:

[0048] S1: Take 100g of positive electrode slurry from the double-helix stirring outlet and the coating machine head respectively and pour them into the homogenization bottle, add 300mL NMP to each, and shake manually for 3-5min until it is completely diluted without precipitation;

[0049] S2: Take a 30 μm filter membrane, wet it with dilute hydrochloric acid and NMP, put it into a Buchner funnel and filter it. After filtering, rinse the surface with NMP several times.

[0050] S3: Place the above filter membrane in a beaker containing NMP and clean it by ultrasonic for 5 minutes;

[0051] S4: Take another 30 μm filter membrane, wet it with dilute hydrochloric acid and deionized water, put it into the Buchner funnel for a second filtration, and rinse the filter membrane surface with deionized water several times after the filtration is completed;

[0052] S5: Take a 0.22 μm filter membrane, wet it with dilute hydrochloric acid and deionized water, then add dilute hydrochloric acid to cover the filter membrane, then add hydrogen peroxide to cover the filter membrane, spread the filtered filter membrane on the surface of the filter membrane, and let it stand for 1 minute;

[0053] S6: Select KSCN as the color developer and add it dropwise to the surface of the above filter membrane. Wait for 3 to 5 minutes. Eight red dots will appear on the filter membrane at the double helix stirring outlet and two red dots will appear on the filter membrane at the coating machine head.

[0054] Comparative Example 1:

[0055] In order to prove that the present invention can qualitatively determine the content of magnetic substances in the slurry, 300g of negative electrode slurry was taken from the main screw outlet and the coating machine head respectively, of which 200g was sent for ICP testing and 100g was subjected to color development reaction. The results are shown in Table 1.

[0056] Table 1

[0057] Slurry location ICP(ppb) Color reaction (number of red dots) Main screw outlet 323.99 5 Coating head 174.57 2

[0058] As can be seen from Table 1, a method for quantitatively detecting magnetic impurities in slurry can calculate the specific content of each metal substance in ppb. This comparative example proves that the colorimetric method has a certain accuracy and can be used as a qualitative judgment before the ICP test.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting metallic foreign matter in lithium ion slurry, characterized in that: The following steps are involved: S1: Take the slurry to be tested, add solvent to dilute and shake well; S2: Filter the shaken slurry for the first time, discard the filtrate, and keep the filter membrane; S3: placing the filtered membrane into a solvent for ultrasonic cleaning; S4: Filter the cleaning liquid for the second time, discard the filtrate, and retain the filter membrane; S5: Place a clean filter membrane on a watch glass, drip an acidic solution and an oxidizing solution onto the surface, spread the filter membrane obtained in step S5 onto the surface of the clean filter membrane, and let it stand; S6: Add a color developer solution to the surfaces of the two overlapping filter membranes obtained in step S5, and wait for color to develop. If color is developed, it is determined that the slurry contains metallic foreign matter; if no color is developed, it is determined that the slurry does not contain metallic foreign matter.

2. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S1, the slurry to be detected is selected from one of positive electrode slurry or negative electrode slurry.

3. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S1, the solvent is one of deionized water and N,N-dimethylformamide (NMP).

4. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S1, the material-liquid ratio of the slurry to be detected and the solvent is 1 g: 1.5-3 mL.

5. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S2, the filtration is specifically as follows: select a filter membrane of appropriate specifications, wash it with dilute hydrochloric acid and solvent respectively, put it into a Buchner funnel, pour in the shaken slurry, and then use the corresponding solvent to repeatedly rinse the container and the surface of the filter membrane to ensure that the main material is filtered cleanly.

6. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S3, ultrasonic cleaning is performed for 3 to 5 minutes.

7. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S5, the clean filter membrane is a 0.22 μm filter membrane.

8. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S5, the acidic solution is selected from dilute hydrochloric acid and dilute nitric acid.

9. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S5, the oxidizing solution is a hydrogen peroxide solution.

10. The method for detecting metallic foreign matter in lithium ion slurry according to claim 1, characterized in that: In step S6, the color developing agent is selected from one of potassium thiocyanate, dicarbohydrazide, and dimethylglyoxime.

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